TY  - JOUR
A1  - Inal, Sahika
A1  - Castellani, Mauro
A1  - Sellinger, Alan
A1  - Neher, Dieter
T1  - Relationship of photophysical properties and the device performance of novel hybrid small-molecular/polymeric solar cells
N2  - We investigate solar cells comprised of a vinazene derivative (HV-BT) as the electron acceptor and the well- known polymer poly(3-hexylthiophene) as the electron donor. In the as-prepared blend, most of the excited state species, including the excimers on HV-BT, are quenched at the heterojunction. Although the photophysical properties of the blends change upon annealing, the blend solar cells largely remain uninfluenced by such treatments. A significant improvement is, however, observed when inducing phase separation at a longer length scale, for example, in solution-processed bilayer devices. Hereby, both the fill factor (FF) and the open circuit voltage are considerably increased, pointing to the importance of the heterojunction topology and the layer composition at the charge extracting contacts. An optimized device exhibits a power conversion efficiency of close to 1%.
Y1  - 2009
UR  - http://www3.interscience.wiley.com/cgi-bin/jhome/10003270
U6  - https://doi.org/10.1002/marc.200900221
SN  - 1022-1336
ER  - 
TY  - JOUR
A1  - Blakesley, James C.
A1  - Neher, Dieter
T1  - Relationship between energetic disorder and open-circuit voltage in bulk heterojunction organic solar cells
JF  - Physical review : B, Condensed matter and materials physics
N2  - We simulate organic bulk heterojunction solar cells. The effects of energetic disorder are incorporated through a Gaussian or exponential model of density of states. Analytical models of open-circuit voltage (V(OC)) are derived from the splitting of quasi-Fermi potentials. Their predictions are backed up by more complex numerical device simulations including effects such as carrier-density-dependent charge-carrier mobilities. It is predicted that the V(OC) depends on: (1) the donor-acceptor energy gap; (2) charge-carrier recombination rates; (3) illumination intensity; (4) the contact work functions (if not in the pinning regime); and (5) the amount of energetic disorder. A large degree of energetic disorder, or a high density of traps, is found to cause significant reductions in V(OC). This can explain why V(OC) is often less than expected in real devices. Energetic disorder also explains the nonideal temperature and intensity dependence of V(OC) and the superbimolecular recombination rates observed in many real bulk heterojunction solar cells.
Y1  - 2011
U6  - https://doi.org/10.1103/PhysRevB.84.075210
SN  - 1098-0121
VL  - 84
IS  - 7
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Nikolis, Vasileios C.
A1  - Benduhn, Johannes
A1  - Holzmueller, Felix
A1  - Piersimoni, Fortunato
A1  - Lau, Matthias
A1  - Zeika, Olaf
A1  - Neher, Dieter
A1  - Koerner, Christian
A1  - Spoltore, Donato
A1  - Vandewal, Koen
T1  - Reducing Voltage Losses in Cascade Organic Solar Cells while Maintaining High External Quantum Efficiencies
JF  - dvanced energy materials
N2  - High photon energy losses limit the open-circuit voltage (V-OC) and power conversion efficiency of organic solar cells (OSCs). In this work, an optimization route is presented which increases the V-OC by reducing the interfacial area between donor (D) and acceptor (A). This optimization route concerns a cascade device architecture in which the introduction of discontinuous interlayers between alpha-sexithiophene (alpha-6T) (D) and chloroboron subnaphthalocyanine (SubNc) (A) increases the V-OC of an alpha-6T/SubNc/SubPc fullerene-free cascade OSC from 0.98 V to 1.16 V. This increase of 0.18 V is attributed solely to the suppression of nonradiative recombination at the D-A interface. By accurately measuring the optical gap (E-opt) and the energy of the charge-transfer state (E-CT) of the studied OSC, a detailed analysis of the overall voltage losses is performed. E-opt - qV(OC) losses of 0.58 eV, which are among the lowest observed for OSCs, are obtained. Most importantly, for the V-OC-optimized devices, the low-energy (700 nm) external quantum efficiency (EQE) peak remains high at 79%, despite a minimal driving force for charge separation of less than 10 meV. This work shows that low-voltage losses can be combined with a high EQE in organic photovoltaic devices.
KW  - energy losses
KW  - nonradiative recombination
KW  - open-circuit voltage
KW  - organic solar cells
KW  - voltage losses
Y1  - 2017
U6  - https://doi.org/10.1002/aenm.201700855
SN  - 1614-6832
SN  - 1614-6840
VL  - 7
SP  - 122
EP  - 136
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Wolff, Christian Michael
A1  - Zu, Fengshuo
A1  - Paulke, Andreas
A1  - Perdigón-Toro, Lorena
A1  - Koch, Norbert
A1  - Neher, Dieter
T1  - Reduced Interface-Mediated Recombination for High Open-Circuit Voltages in CH3NH3PbI3 Solar Cells
JF  - Advanced materials
N2  - Perovskite solar cells with all-organic transport layers exhibit efficiencies rivaling their counterparts that employ inorganic transport layers, while avoiding high-temperature processing. Herein, it is investigated how the choice of the fullerene derivative employed in the electron-transporting layer of inverted perovskite cells affects the open-circuit voltage (V-OC). It is shown that nonradiative recombination mediated by the electron-transporting layer is the limiting factor for the V-OC in the cells. By inserting an ultrathin layer of an insulating polymer between the active CH3NH3PbI3 perovskite and the fullerene, an external radiative efficiency of up to 0.3%, a V-OC as high as 1.16 V, and a power conversion efficiency of 19.4% are realized. The results show that the reduction of nonradiative recombination due to charge-blocking at the perovskite/organic interface is more important than proper level alignment in the search for ideal selective contacts toward high V-OC and efficiency.
KW  - electron-transport layers
KW  - nonradiative recombination
KW  - open-circuit voltage
KW  - perovskite solar cells
Y1  - 2017
U6  - https://doi.org/10.1002/adma.201700159
SN  - 0935-9648
SN  - 1521-4095
VL  - 29
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Würfel, Uli
A1  - Perdigón-Toro, Lorena
A1  - Kurpiers, Jona
A1  - Wolff, Christian Michael
A1  - Caprioglio, Pietro
A1  - Rech, Jeromy James
A1  - Zhu, Jingshuai
A1  - Zhan, Xiaowei
A1  - You, Wei
A1  - Shoaee, Safa
A1  - Neher, Dieter
A1  - Stolterfoht, Martin
T1  - Recombination between Photogenerated and Electrode-Induced Charges Dominates the Fill Factor Losses in Optimized Organic Solar Cells
JF  - The journal of physical chemistry letters
N2  - Charge extraction in organic solar cells (OSCs) is commonly believed to be limited by bimolecular recombination of photogenerated charges. However, the fill factor of OSCs is usually almost entirely governed by recombination processes that scale with the first order of the light intensity. This linear loss was often interpreted to be a consequence of geminate or trap-assisted recombination. Numerical simulations show that this linear dependence is a direct consequence of the large amount of excess dark charge near the contact. The first-order losses increase with decreasing mobility of minority carriers, and we discuss the impact of several material and device parameters on this loss mechanism. This work highlights that OSCs are especially vulnerable to injected charges as a result of their poor charge transport properties. This implies that dark charges need to be better accounted for when interpreting electro-optical measurements and charge collection based on simple figures of merit.
Y1  - 2019
U6  - https://doi.org/10.1021/acs.jpclett.9b01175
SN  - 1948-7185
VL  - 10
IS  - 12
SP  - 3473
EP  - 3480
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Wang, Qiong
A1  - Mosconi, Edoardo
A1  - Wolff, Christian Michael
A1  - Li, Junming
A1  - Neher, Dieter
A1  - De Angelis, Filippo
A1  - Suranna, Gian Paolo
A1  - Grisorio, Roberto
A1  - Abate, Antonio
T1  - Rationalizing the molecular design of hole-selective contacts to improve charge extraction in Perovskite solar cells
JF  - dvanced energy materials
N2  - Two new hole selective materials (HSMs) based on dangling methylsulfanyl groups connected to the C-9 position of the fluorene core are synthesized and applied in perovskite solar cells. Being structurally similar to a half of Spiro-OMeTAD molecule, these HSMs (referred as FS and DFS) share similar redox potentials but are endowed with slightly higher hole mobility, due to the planarity and large extension of their structure. Competitive power conversion efficiency (up to 18.6%) is achieved by using the new HSMs in suitable perovskite solar cells. Time-resolved photoluminescence decay measurements and electrochemical impedance spectroscopy show more efficient charge extraction at the HSM/perovskite interface with respect to Spiro-OMeTAD, which is reflected in higher photocurrents exhibited by DFS/FS-integrated perovskite solar cells. Density functional theory simulations reveal that the interactions of methylammonium with methylsulfanyl groups in DFS/FS strengthen their electrostatic attraction with the perovskite surface, providing an additional path for hole extraction compared to the sole presence of methoxy groups in Spiro-OMeTAD. Importantly, the low-cost synthesis of FS makes it significantly attractive for the future commercialization of perovskite solar cells.
KW  - hole extraction
KW  - hole selective materials
KW  - perovskite solar cells
KW  - sulfur
KW  - triple-cation perovskite
Y1  - 2019
U6  - https://doi.org/10.1002/aenm.201900990
SN  - 1614-6832
SN  - 1614-6840
VL  - 9
IS  - 28
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Turner, Sarah T.
A1  - Pingel, Patrick
A1  - Steyrleuthner, Robert
A1  - Crossland, Edward J. W.
A1  - Ludwigs, Sabine
A1  - Neher, Dieter
T1  - Quantitative analysis of bulk heterojunction films using linear absorption spectroscopy and solar cell performance
JF  - Advanced functional materials
N2  - A fundamental understanding of the relationship between the bulk morphology and device performance is required for the further development of bulk heterojunction organic solar cells. Here, non-optimized (chloroform cast) and nearly optimized (solvent-annealed o-dichlorobenzene cast) P3HT:PCBM blend films treated over a range of annealing temperatures are studied via optical and photovoltaic device measurements. Parameters related to the P3HT aggregate morphology in the blend are obtained through a recently established analytical model developed by F. C. Spano for the absorption of weakly interacting H-aggregates. Thermally induced changes are related to the glass transition range of the blend. In the chloroform prepared devices, the improvement in device efficiency upon annealing within the glass transition range can be attributed to the growth of P3HT aggregates, an overall increase in the percentage of chain crystallinity, and a concurrent increase in the hole mobilities. Films treated above the glass transition range show an increase in efficiency and fill factor not only associated with the change in chain crystallinity, but also with a decrease in the energetic disorder. On the other hand, the properties of the P3HT phase in the solvent-annealed o-dichlorobenzene cast blends are almost indistinguishable from those of the corresponding pristine P3HT layer and are only weakly affected by thermal annealing. Apparently, slow drying of the blend allows the P3HT chains to crystallize into large domains with low degrees of intra- and interchain disorder. This morphology appears to be most favorable for the efficient generation and extraction of charges.
KW  - Organic electronics
KW  - morphology
KW  - solar cells
KW  - mobility
KW  - absorption spectroscopy
Y1  - 2011
U6  - https://doi.org/10.1002/adfm.201101583
SN  - 1616-301X
VL  - 21
IS  - 24
SP  - 4640
EP  - 4652
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Phuong, Le Quang
A1  - Hosseini, Seyed Mehrdad
A1  - Sandberg, Oskar J.
A1  - Zou, Yingping
A1  - Woo, Han Young
A1  - Neher, Dieter
A1  - Shoaee, Safa
T1  - Quantifying quasi-fermi level splitting and open-circuit voltage losses in highly efficient nonfullerene organic solar cells
JF  - Solar RRL
N2  - The power conversion efficiency (PCE) of state-of-the-art organic solar cells is still limited by significant open-circuit voltage (V-OC) losses, partly due to the excitonic nature of organic materials and partly due to ill-designed architectures. Thus, quantifying different contributions of the V-OC losses is of importance to enable further improvements in the performance of organic solar cells. Herein, the spectroscopic and semiconductor device physics approaches are combined to identify and quantify losses from surface recombination and bulk recombination. Several state-of-the-art systems that demonstrate different V-OC losses in their performance are presented. By evaluating the quasi-Fermi level splitting (QFLS) and the V-OC as a function of the excitation fluence in nonfullerene-based PM6:Y6, PM6:Y11, and fullerene-based PPDT2FBT:PCBM devices with different architectures, the voltage losses due to different recombination processes occurring in the active layers, the transport layers, and at the interfaces are assessed. It is found that surface recombination at interfaces in the studied solar cells is negligible, and thus, suppressing the non-radiative recombination in the active layers is the key factor to enhance the PCE of these devices. This study provides a universal tool to explain and further improve the performance of recently demonstrated high-open-circuit-voltage organic solar cells.
KW  - nonfullerene acceptors
KW  - organic solar cells
KW  - quasi-Fermi level
KW  - splitting
KW  - quasi-steady-state photoinduced absorptions
KW  - surface
KW  - recombinations
KW  - voltage losses
Y1  - 2020
U6  - https://doi.org/10.1002/solr.202000649
SN  - 2367-198X
VL  - 5
IS  - 1
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - GEN
A1  - Phuong, Le Quang
A1  - Hosseini, Seyed Mehrdad
A1  - Sandberg, Oskar J.
A1  - Zou, Yingping
A1  - Woo, Han Young
A1  - Neher, Dieter
A1  - Shoaee, Safa
T1  - Quantifying quasi-fermi level splitting and open-circuit voltage losses in highly efficient nonfullerene organic solar cells
T2  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
N2  - The power conversion efficiency (PCE) of state-of-the-art organic solar cells is still limited by significant open-circuit voltage (V-OC) losses, partly due to the excitonic nature of organic materials and partly due to ill-designed architectures. Thus, quantifying different contributions of the V-OC losses is of importance to enable further improvements in the performance of organic solar cells. Herein, the spectroscopic and semiconductor device physics approaches are combined to identify and quantify losses from surface recombination and bulk recombination. Several state-of-the-art systems that demonstrate different V-OC losses in their performance are presented. By evaluating the quasi-Fermi level splitting (QFLS) and the V-OC as a function of the excitation fluence in nonfullerene-based PM6:Y6, PM6:Y11, and fullerene-based PPDT2FBT:PCBM devices with different architectures, the voltage losses due to different recombination processes occurring in the active layers, the transport layers, and at the interfaces are assessed. It is found that surface recombination at interfaces in the studied solar cells is negligible, and thus, suppressing the non-radiative recombination in the active layers is the key factor to enhance the PCE of these devices. This study provides a universal tool to explain and further improve the performance of recently demonstrated high-open-circuit-voltage organic solar cells.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1384 
KW  - nonfullerene acceptors
KW  - organic solar cells
KW  - quasi-Fermi level
KW  - splitting
KW  - quasi-steady-state photoinduced absorptions
KW  - surface
KW  - recombinations
KW  - voltage losses
Y1  - 2020
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-570018
SN  - 1866-8372
IS  - 1
ER  - 
TY  - JOUR
A1  - Albrecht, Steve
A1  - Tumbleston, John R.
A1  - Janietz, Silvia
A1  - Dumsch, Ines
A1  - Allard, Sybille
A1  - Scherf, Ullrich
A1  - Ade, Harald W.
A1  - Neher, Dieter
T1  - Quantifying charge extraction in organic solar cells: The case of fluorinated PCPDTBT
JF  - The journal of physical chemistry letters
N2  - We introduce a new and simple method to quantify the effective extraction mobility in organic solar cells at low electric fields and charge carrier densities comparable to operation conditions under one sun illumination. By comparing steady-state carrier densities at constant illumination intensity and under open-circuit conditions, the gradient of the quasi-Fermi potential driving the current is estimated as a function of external bias and charge density. These properties are then related to the respective steady-state current to determine the effective extraction mobility. The new technique is applied to different derivatives of the well-known low-band-gap polymer PCPDTBT blended with PC70BM. We show that the slower average extraction due to lower mobility accounts for the moderate fill factor when solar cells are fabricated with mono- or difluorinated PCPDTBT. This lower extraction competes with improved generation and reduced nongeminate recombination, rendering the monofluorinated derivative the most efficient donor polymer.
Y1  - 2014
U6  - https://doi.org/10.1021/jz500457b
SN  - 1948-7185
VL  - 5
IS  - 7
SP  - 1131
EP  - 1138
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Le Corre, Vincent M.
A1  - Diekmann, Jonas
A1  - Peña-Camargo, Francisco
A1  - Thiesbrummel, Jarla
A1  - Tokmoldin, Nurlan
A1  - Gutierrez-Partida, Emilio
A1  - Peters, Karol Pawel
A1  - Perdigón-Toro, Lorena
A1  - Futscher, Moritz H.
A1  - Lang, Felix
A1  - Warby, Jonathan
A1  - Snaith, Henry J.
A1  - Neher, Dieter
A1  - Stolterfoht, Martin
T1  - Quantification of efficiency losses due to mobile ions in Perovskite solar cells via fast hysteresis measurements
JF  - Solar RRL
N2  - Perovskite semiconductors differ from most inorganic and organic semiconductors due to the presence of mobile ions in the material. Although the phenomenon is intensively investigated, important questions such as the exact impact of the mobile ions on the steady-state power conversion efficiency (PCE) and stability remain. Herein, a simple method is proposed to estimate the efficiency loss due to mobile ions via "fast-hysteresis" measurements by preventing the perturbation of mobile ions out of their equilibrium position at fast scan speeds (approximate to 1000 V s(-1)). The "ion-free" PCE is between 1% and 3% higher than the steady-state PCE, demonstrating the importance of ion-induced losses, even in cells with low levels of hysteresis at typical scan speeds (approximate to 100mv s(-1)). The hysteresis over many orders of magnitude in scan speed provides important information on the effective ion diffusion constant from the peak hysteresis position. The fast-hysteresis measurements are corroborated by transient charge extraction and capacitance measurements and numerical simulations, which confirm the experimental findings and provide important insights into the charge carrier dynamics. The proposed method to quantify PCE losses due to field screening induced by mobile ions clarifies several important experimental observations and opens up a large range of future experiments.
KW  - hysteresis
KW  - mobile ions
KW  - perovskite solar cells
Y1  - 2021
U6  - https://doi.org/10.1002/solr.202100772
SN  - 2367-198X
VL  - 6
IS  - 4
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Hosseini, Seyed Mehrdad
A1  - Tokmoldin, Nurlan
A1  - Lee, Young Woong
A1  - Zou, Yingping
A1  - Woo, Han Young
A1  - Neher, Dieter
A1  - Shoaee, Safa
T1  - Putting order into PM6:Y6 solar cells to reduce the langevin recombination in 400 nm thick junction
JF  - Solar RRL
N2  - Increasing the active layer thickness without sacrificing the power conversion efficiency (PCE) is one of the great challenges faced by organic solar cells (OSCs) for commercialization. Recently, PM6:Y6 as an OSC based on a non-fullerene acceptor (NFA) has excited the community because of its PCE reaching as high as 15.9%; however, by increasing the thickness, the PCE drops due to the reduction of the fill factor (FF). This drop is attributed to change in mobility ratio with increasing thickness. Furthermore, this work demonstrates that by regulating the packing and the crystallinity of the donor and the acceptor, through volumetric content of chloronaphthalene (CN) as a solvent additive, one can improve the FF of a thick PM6:Y6 device (approximate to 400 nm) from 58% to 68% (PCE enhances from 12.2% to 14.4%). The data indicate that the origin of this enhancement is the reduction of the structural and energetic disorders in the thick device with 1.5% CN compared with 0.5% CN. This correlates with improved electron and hole mobilities and a 50% suppressed bimolecular recombination, such that the non-Langevin reduction factor is 180 times. This work reveals the role of disorder on the charge extraction and bimolecular recombination of NFA-based OSCs.
KW  - charge carrier extraction
KW  - energetic disorders
KW  - non-fullerene acceptors
KW  - non-Langevin reduction factors
KW  - thick junctions
Y1  - 2020
U6  - https://doi.org/10.1002/solr.202000498
SN  - 2367-198X
VL  - 4
IS  - 11
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Kurpiers, Jona
A1  - Ferron, Thomas
A1  - Roland, Steffen
A1  - Jakoby, Marius
A1  - Thiede, Tobias
A1  - Jaiser, Frank
A1  - Albrecht, Steve
A1  - Janietz, Silvia
A1  - Collins, Brian A.
A1  - Howard, Ian A.
A1  - Neher, Dieter
T1  - Probing the pathways of free charge generation in organic bulk heterojunction solar cells
JF  - Nature Communications
N2  - The fact that organic solar cells perform efficiently despite the low dielectric constant of most photoactive blends initiated a long-standing debate regarding the dominant pathways of free charge formation. Here, we address this issue through the accurate measurement of the activation energy for free charge photogeneration over a wide range of photon energy, using the method of time-delayed collection field. For our prototypical low bandgap polymer:fullerene blends, we find that neither the temperature nor the field dependence of free charge generation depend on the excitation energy, ruling out an appreciable contribution to free charge generation though hot carrier pathways. On the other hand, activation energies are on the order of the room temperature thermal energy for all studied blends. We conclude that charge generation in such devices proceeds through thermalized charge transfer states, and that thermal energy is sufficient to separate most of these states into free charges.
Y1  - 2018
U6  - https://doi.org/10.1038/s41467-018-04386-3
SN  - 2041-1723
VL  - 9
PB  - Nature Publ. Group
CY  - London
ER  - 
TY  - JOUR
A1  - Kietzke, Thomas
A1  - Stiller, Burkhard
A1  - Landfester, Katharina
A1  - Montenegro, Rivelino V. D.
A1  - Neher, Dieter
T1  - Probing the local optical properties of layers prepared from polymer nanoparticles
N2  - It is well known that the performance of solar cells based on a blend of hole-accepting and electron-accepting conjugated polymers as the active material depend crucially on the length scale of the resulting phase separated morphology. However, a direct control of this morphology is difficult if the layer is prepared from an organic solvent. To circumvent this difficulty, recently a universal method to fabricate defined nano-structured blend layer using nanoparticles dispersed in water was demonstrated. These nanoparticles were prepared with the miniemulsion method, which allows for the preparation of semiconducting polymer nanospheres (SPNs) with diameters in the range of 30 to 300 nanometres. Since the process starts from the active material dissolved in a common solvent, it can be applied to the fabrication of nanoparticles of blends of polymers with oligomers or even with inorganic materials. We present here for the first time scanning near field optical microscopy (SNOM) investigations on these novel nanostructured polymer layers. We show that by spin-coating a mixture of two different dispersions a nanoparticle monolayer with a statistically distribution of the nanoparticles can be obtained. Mixing conjugated polymer nanoparticles with some inert particles like polystyrene beads may allow for the preparation of nano-sized light emitters
Y1  - 2005
SN  - 0379-6779
ER  - 
TY  - JOUR
A1  - Zu, Fengshuo
A1  - Schultz, Thorsten
A1  - Wolff, Christian Michael
A1  - Shin, Dongguen
A1  - Frohloff, Lennart
A1  - Neher, Dieter
A1  - Amsalem, Patrick
A1  - Koch, Norbert
T1  - Position-locking of volatile reaction products by atmosphere and capping layers slows down photodecomposition of methylammonium lead triiodide perovskite
JF  - RSC Advances
N2  - The remarkable progress of metal halide perovskites in photovoltaics has led to the power conversion efficiency approaching 26%. However, practical applications of perovskite-based solar cells are challenged by the stability issues, of which the most critical one is photo-induced degradation. Bare CH3NH3PbI3 perovskite films are known to decompose rapidly, with methylammonium and iodine as volatile species and residual solid PbI2 and metallic Pb, under vacuum under white light illumination, on the timescale of minutes. We find, in agreement with previous work, that the degradation is non-uniform and proceeds predominantly from the surface, and that illumination under N-2 and ambient air (relative humidity 20%) does not induce substantial degradation even after several hours. Yet, in all cases the release of iodine from the perovskite surface is directly identified by X-ray photoelectron spectroscopy. This goes in hand with a loss of organic cations and the formation of metallic Pb. When CH3NH3PbI3 films are covered with a few nm thick organic capping layer, either charge selective or non-selective, the rapid photodecomposition process under ultrahigh vacuum is reduced by more than one order of magnitude, and becomes similar in timescale to that under N-2 or air. We conclude that the light-induced decomposition reaction of CH3NH3PbI3, leading to volatile methylammonium and iodine, is largely reversible as long as these products are restrained from leaving the surface. This is readily achieved by ambient atmospheric pressure, as well as a thin organic capping layer even under ultrahigh vacuum. In addition to explaining the impact of gas pressure on the stability of this perovskite, our results indicate that covalently "locking" the position of perovskite components at the surface or an interface should enhance the overall photostability.
Y1  - 2020
U6  - https://doi.org/10.1039/d0ra03572f
SN  - 2046-2069
VL  - 10
IS  - 30
SP  - 17534
EP  - 17542
PB  - Royal Society of Chemistry
CY  - Cambridge
ER  - 
TY  - JOUR
A1  - Yang, X. H.
A1  - Neher, Dieter
T1  - Polymer electrophosphorescence devices with high power conversion efficiencies
N2  - We demonstrate efficient single-layer polymer phosphorescent light-emitting devices based on a green-emitting iridium complex and a polymer host co-doped with electron-transporting and hole-transporting molecules. These devices can be operated at relatively low voltages, resulting in a power conversion efficiency of up to 24 lm/W at luminous efficiencies exceeding 30 cd/A. The overall performances of these devices suggest that efficient electrophosphorescent devices with acceptable operating voltages can be achieved in very simple device structures fabricated by spin coating. (C) 2004 American Institute of Physics
Y1  - 2004
SN  - 0003-6951
ER  - 
TY  - JOUR
A1  - Luszczynska, Beata
A1  - Dobruchowska, Ewa
A1  - Glowacki, Ireneusz
A1  - Ulanski, Jacek
A1  - Jaiser, Frank
A1  - Yang, Xiaohui
A1  - Neher, Dieter
A1  - Danel, Andrzej
T1  - Poly(N-vinylcarbazole) doped with a pyrazoloquinoline dye : a deep blue light-emitting composite for light- emitting diode applications
N2  - We investigated the spectral properties of light-emitting diodes based on a deep blue-emitting pyrazoloquinoline dye doped into a poly(N-vinylcarbazole)-based matrix. Even though the electroluminescence (EL) of the host is redshifted and broadened with respect to the emission of the dye, the EL spectrum becomes fully dominated by the dye emission at concentrations of ca. 2 wt %. This is attributed to a competition of exciplex formation on the matrix and exciton formation on the dye.
Y1  - 2006
UR  - http://jap.aip.org/
U6  - https://doi.org/10.1063/1.2162268
SN  - 0021-8979
ER  - 
TY  - JOUR
A1  - Bauer, C.
A1  - Umbasch, G.
A1  - Giessen, H.
A1  - Meisel, A.
A1  - Nothofer, Heinz-Georg
A1  - Neher, Dieter
A1  - Scherf, Ullrich
A1  - Marth, R.
T1  - Polarized Photoluminescence and Spectral Narrowing in an oriented Polyfluorene Thin Film
Y1  - 2000
ER  - 
TY  - JOUR
A1  - Miteva, T.
A1  - Meisel, A.
A1  - Nothofer, Heinz-Georg
A1  - Scherf, Ullrich
A1  - Knoll, W.
A1  - Neher, Dieter
A1  - Grell, M.
A1  - Lupo, D.
A1  - Yasuda, A.
T1  - Polarized electroluminescence from highly aligned liquid-crystalline polymers
Y1  - 2000
ER  - 
TY  - JOUR
A1  - Zen, Achmad
A1  - Neher, Dieter
A1  - Bauer, C.
A1  - Asawapirom, Udom
A1  - Scherf, Ullrich
A1  - Hagen, R.
A1  - Kostromine, S.
A1  - Mahrt, R. F.
T1  - Polarization-sensitive photoconductivity in aligned polyfluorene layers
Y1  - 2002
ER  - 
TY  - JOUR
A1  - Pralle, Martin U.
A1  - Urayama, Kenji
A1  - Tew, Gregory N.
A1  - Neher, Dieter
A1  - Wegner, Gerhard
A1  - Stupp, Samuel I.
T1  - Piezoelectricity in polar supramolecular materials
Y1  - 2000
ER  - 
TY  - JOUR
A1  - Däubler, Thomas Karl
A1  - Pfeiffer, S.
A1  - Hörhold, Hans-Heinrich
A1  - Neher, Dieter
T1  - Photogeneration of charge carriers in segmented arylamino-PPV derivatives
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Däubler, Thomas Karl
A1  - Glowacki, Ireneusz
A1  - Scherf, Ullrich
A1  - Ulanski, J.
A1  - Hörhold, Hans-Heinrich
A1  - Neher, Dieter
T1  - Photogeneration and transport of charge carriers in hybrid materials of conjugated polymers and dye-sensitized TiO2
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Kniepert, Juliane
A1  - Schubert, Marcel
A1  - Blakesley, James C.
A1  - Neher, Dieter
T1  - Photogeneration and recombination in P3HT/PCBM solar cells probed by time-delayed collection field experiments
JF  - The journal of physical chemistry letters
N2  - Time-delayed collection field (TDCF) experiments are performed on bulk heterojunction solar cells comprised of a blend of poly(3-hexylthiophene) and [6,6]-phenyl C-71 butyric acid methyl ester. TDCF is analogous to a pump-probe experiment using optical excitation and an electrical probe with a resolution of < 100 ns. The number of free charge carriers extracted after a short delay is found to be independent of the electric field during illumination. Also, experiments performed with a variable delay between the optical excitation and the electrical probe do not reveal any evidence for the generation of charge via field-assisted dissociation of bound long-lived polaron pairs. Photocurrent transients are well fitted by computational drift diffusion simulations with only direct generation of free charge carriers. With increasing delay times between pump and probe, two loss mechanisms are identified; first, charge-carriers are swept out of the device by the internal electric field, and second, bimolecular recombination of the remaining carriers takes place with a reduced recombination coefficient.
Y1  - 2011
U6  - https://doi.org/10.1021/jz200155b
SN  - 1948-7185
VL  - 2
IS  - 7
SP  - 700
EP  - 705
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Kulikovsky, Lazar
A1  - Neher, Dieter
A1  - Mecher, E.
A1  - Meerholz, Klaus
A1  - Horhold, H. H.
A1  - Ostroverkhova, O.
T1  - Photocurrent dynamics in a poly(phenylene vinylene)-based photorefractive composite
N2  - All parameters describing the charge carrier dynamics in a poly(phenylene vinylene)-based photorefractive (PR) composite relevant to PR grating dynamics were determined using photoconductivity studies under various illumination conditions. In particular, the values of the coefficients for trap filling and recombination of charges with ionized sensitizer molecules could be extracted independently. It is concluded that the PR growth time without preillumination is mostly determined by the competition between deep trap filling and recombination with ionized sensitizer molecules. Further, the pronounced increase in PR speed upon homogeneous preillumination (gating) as reported recently is quantitatively explained by deep trap filling
Y1  - 2004
SN  - 1098-0121
ER  - 
TY  - JOUR
A1  - Sianova, D.
A1  - Zen, Achmad
A1  - Nothofer, Heinz-Georg
A1  - Asawapirom, Udom
A1  - Scherf, Ullrich
A1  - Hagen, R.
A1  - Bieringer, Thomas
A1  - Kostromine, S.
A1  - Neher, Dieter
T1  - Photoaddressable alignment layers for fluorescent polymers in polarized electroluminescence devices
Y1  - 2002
ER  - 
TY  - JOUR
A1  - Ilnytskyi, Jaroslav
A1  - Saphiannikova, Marina
A1  - Neher, Dieter
T1  - Photo-induced deformations in azobenzene-containing side-chain polymers : molecular dynamics study
N2  - We perform molecular dynamics simulations of azobenzene containing side-chain liquid crystalline polymer subject to an external model field that mimicks the reorientations of the azobenzenes upon irradiation with polarized light. The smectic phase of the polymer is studied with the field applied parallel to the nematic director, forcing the trans isomers to reorient perpendicularly to the field (the direction of which can be assosiated with the light polarization). The coupling between the reorientation of azobenzenes and mechanical deformation of the sample is found to depend on the field strength. In a weak field the original smectic order is melted gradually with no apparent change in the simulation box shape, whereas in a strong field two regimes are observed. During the first one a rapid melting of the liquid crystalline order is accompanied by the contraction of the polymer along the field direction (the effect similar to the one observed experimentally in azopenzene containing elastomers). During the slower second regime, the smectic layers are rebuilt to accomodate the preferential direction of chromophores perperdicular to the field.
Y1  - 2006
UR  - http://www.icmp.lviv.ua/journal/Contents.html
SN  - 1607-324X
ER  - 
TY  - JOUR
A1  - Brinkmann, Kai Oliver
A1  - Becker, Tim
A1  - Zimmermann, Florian
A1  - Kreusel, Cedric
A1  - Gahlmann, Tobias
A1  - Theisen, Manuel
A1  - Haeger, Tobias
A1  - Olthof, Selina
A1  - Tückmantel, Christian
A1  - Günster, M.
A1  - Maschwitz, Timo
A1  - Göbelsmann, Fabian
A1  - Koch, Christine
A1  - Hertel, Dirk
A1  - Caprioglio, Pietro
A1  - Peña-Camargo, Francisco
A1  - Perdigón-Toro, Lorena
A1  - Al-Ashouri, Amran
A1  - Merten, Lena
A1  - Hinderhofer, Alexander
A1  - Gomell, Leonie
A1  - Zhang, Siyuan
A1  - Schreiber, Frank
A1  - Albrecht, Steve
A1  - Meerholz, Klaus
A1  - Neher, Dieter
A1  - Stolterfoht, Martin
A1  - Riedl, Thomas
T1  - Perovskite-organic tandem solar cells with indium oxide interconnect
JF  - Nature
N2  - Multijunction solar cells can overcome the fundamental efficiency limits of single-junction devices. The bandgap tunability of metal halide perovskite solar cells renders them attractive for multijunction architectures(1). Combinations with silicon and copper indium gallium selenide (CIGS), as well as all-perovskite tandem cells, have been reported(2-5). Meanwhile, narrow-gap non-fullerene acceptors have unlocked skyrocketing efficiencies for organic solar cells(6,7). Organic and perovskite semiconductors are an attractive combination, sharing similar processing technologies. Currently, perovskite-organic tandems show subpar efficiencies and are limited by the low open-circuit voltage (V-oc) of wide-gap perovskite cells(8) and losses introduced by the interconnect between the subcells(9,10). Here we demonstrate perovskite-organic tandem cells with an efficiency of 24.0 per cent (certified 23.1 per cent) and a high V-oc of 2.15 volts. Optimized charge extraction layers afford perovskite subcells with an outstanding combination of high V-oc and fill factor. The organic subcells provide a high external quantum efficiency in the near-infrared and, in contrast to paradigmatic concerns about limited photostability of non-fullerene cells(11), show an outstanding operational stability if excitons are predominantly generated on the non-fullerene acceptor, which is the case in our tandems. The subcells are connected by an ultrathin (approximately 1.5 nanometres) metal-like indium oxide layer with unprecedented low optical/electrical losses. This work sets a milestone for perovskite-organic tandems, which outperform the best p-i-n perovskite single junctions(12) and are on a par with perovskite-CIGS and all-perovskite multijunctions(13).
Y1  - 2022
U6  - https://doi.org/10.1038/s41586-022-04455-0
SN  - 0028-0836
SN  - 1476-4687
VL  - 604
IS  - 7905
SP  - 280
EP  - 286
PB  - Nature Research
CY  - Berlin
ER  - 
TY  - JOUR
A1  - Deschler, Felix
A1  - Neher, Dieter
A1  - Schmidt-Mende, Lukas
T1  - Perovskite semiconductors for next generation optoelectronic applications
JF  - APL Materials
Y1  - 2019
U6  - https://doi.org/10.1063/1.5119744
SN  - 2166-532X
VL  - 7
IS  - 8
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Moule, Adam J.
A1  - Neher, Dieter
A1  - Turner, Sarah T.
ED  - Ludwigs, S
T1  - P3HT-Based solar cells: structural properties and photovoltaic performance
JF  - Advances in Polymer Science
JF  - Advances in Polymer Science
N2  - Each year we are bombarded with B.Sc. and Ph.D. applications from students that want to improve the world. They have learned that their future depends on changing the type of fuel we use and that solar energy is our future. The hope and energy of these young people will transform future energy technologies, but it will not happen quickly. Organic photovoltaic devices are easy to sketch, but the materials, processing steps, and ways of measuring the properties of the materials are very complicated. It is not trivial to make a systematic measurement that will change the way other research groups think or practice. In approaching this chapter, we thought about what a new researcher would need to know about organic photovoltaic devices and materials in order to have a good start in the subject. Then, we simplified that to focus on what a new researcher would need to know about poly-3-hexylthiophene: phenyl-C61-butyric acid methyl ester blends (P3HT: PCBM) to make research progress with these materials. This chapter is by no means authoritative or a compendium of all things on P3HT: PCBM. We have selected to explain how the sample fabrication techniques lead to control of morphology and structural features and how these morphological features have specific optical and electronic consequences for organic photovoltaic device applications.
KW  - Free carrier generation
KW  - Non-geminate recombination
KW  - Organic solar cells
Y1  - 2014
SN  - 978-3-662-45145-8; 978-3-662-45144-1
U6  - https://doi.org/10.1007/12_2014_289
SN  - 0065-3195
VL  - 265
SP  - 181
EP  - 232
PB  - Springer
CY  - Berlin
ER  - 
TY  - JOUR
A1  - Pingel, Patrick
A1  - Arvind, Malavika
A1  - Kölln, Lisa
A1  - Steyrleuthner, Robert
A1  - Kraffert, Felix
A1  - Behrends, Jan
A1  - Janietz, Silvia
A1  - Neher, Dieter
T1  - p-Type Doping of Poly(3-hexylthiophene) with the Strong Lewis Acid Tris(pentafluorophenyl)borane
JF  - Advanced electronic materials
N2  - State-of-the-art p-type doping of organic semiconductors is usually achieved by employing strong -electron acceptors, a prominent example being tetrafluorotetracyanoquinodimethane (F(4)TCNQ). Here, doping of the semiconducting model polymer poly(3-hexylthiophene), P3HT, using the strong Lewis acid tris(pentafluorophenyl)borane (BCF) as a dopant, is investigated by admittance, conductivity, and electron paramagnetic resonance measurements. The electrical characteristics of BCF- and F(4)TCNQ-doped P3HT layers are shown to be very similar in terms of the mobile hole density and the doping efficiency. Roughly 18% of the employed dopants create mobile holes in either F-4 TCNQ- or BCF-doped P3HT, while the majority of doping-induced holes remain strongly Coulomb-bound to the dopant anions. Despite similar hole densities, conductivity and hole mobility are higher in BCF-doped P3HT layers than in F(4)TCNQ-doped samples. This and the good solubility in many organic solvents render BCF very useful for p-type doping of organic semiconductors.
KW  - charge carrier transport
KW  - charge transfer
KW  - conductivity
KW  - molecular doping
KW  - organic semiconductors
Y1  - 2016
U6  - https://doi.org/10.1002/aelm.201600204
SN  - 2199-160X
VL  - 2
PB  - Wiley-Blackwell
CY  - Hoboken
ER  - 
TY  - JOUR
A1  - Proctor, Christopher M.
A1  - Albrecht, Steve
A1  - Kuik, Martijn
A1  - Neher, Dieter
A1  - Thuc-Quyen Nguyen, 
T1  - Overcoming geminate recombination and enhancing extraction in solution-processed small molecule solar cells
JF  - dvanced energy materials
Y1  - 2014
U6  - https://doi.org/10.1002/aenm.201400230
SN  - 1614-6832
SN  - 1614-6840
VL  - 4
IS  - 10
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - GEN
A1  - Ye, Fangyuan
A1  - Zhang, Shuo
A1  - Warby, Jonathan
A1  - Wu, Jiawei
A1  - Gutierrez-Partida, Emilio
A1  - Lang, Felix
A1  - Shah, Sahil
A1  - Saglamkaya, Elifnaz
A1  - Sun, Bowen
A1  - Zu, Fengshuo
A1  - Shoaee, Safa
A1  - Wang, Haifeng
A1  - Stiller, Burkhard
A1  - Neher, Dieter
A1  - Zhu, Wei-Hong
A1  - Stolterfoht, Martin
A1  - Wu, Yongzhen
T1  - Overcoming C₆₀-induced interfacial recombination in inverted perovskite solar cells by electron-transporting carborane
T2  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
N2  - Inverted perovskite solar cells still suffer from significant non-radiative recombination losses at the perovskite surface and across the perovskite/C₆₀ interface, limiting the future development of perovskite-based single- and multi-junction photovoltaics. Therefore, more effective inter- or transport layers are urgently required. To tackle these recombination losses, we introduce ortho-carborane as an interlayer material that has a spherical molecular structure and a three-dimensional aromaticity. Based on a variety of experimental techniques, we show that ortho-carborane decorated with phenylamino groups effectively passivates the perovskite surface and essentially eliminates the non-radiative recombination loss across the perovskite/C₆₀ interface with high thermal stability. We further demonstrate the potential of carborane as an electron transport material, facilitating electron extraction while blocking holes from the interface. The resulting inverted perovskite solar cells deliver a power conversion efficiency of over 23% with a low non-radiative voltage loss of 110 mV, and retain >97% of the initial efficiency after 400 h of maximum power point tracking. Overall, the designed carborane based interlayer simultaneously enables passivation, electron-transport and hole-blocking and paves the way toward more efficient and stable perovskite solar cells.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1317 
Y1  - 2022
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-587705
SN  - 1866-8372
IS  - 1317
ER  - 
TY  - JOUR
A1  - Ye, Fangyuan
A1  - Zhang, Shuo
A1  - Warby, Jonathan
A1  - Wu, Jiawei
A1  - Gutierrez-Partida, Emilio
A1  - Lang, Felix
A1  - Shah, Sahil
A1  - Saglamkaya, Elifnaz
A1  - Sun, Bowen
A1  - Zu, Fengshuo
A1  - Shoai, Safa
A1  - Wang, Haifeng
A1  - Stiller, Burkhard
A1  - Neher, Dieter
A1  - Zhu, Wei-Hong
A1  - Stolterfoht, Martin
A1  - Wu, Yongzhen
T1  - Overcoming C₆₀-induced interfacial recombination in inverted perovskite solar cells by electron-transporting carborane
JF  - Nature Communications
N2  - Inverted perovskite solar cells still suffer from significant non-radiative recombination losses at the perovskite surface and across the perovskite/C₆₀ interface, limiting the future development of perovskite-based single- and multi-junction photovoltaics. Therefore, more effective inter- or transport layers are urgently required. To tackle these recombination losses, we introduce ortho-carborane as an interlayer material that has a spherical molecular structure and a three-dimensional aromaticity. Based on a variety of experimental techniques, we show that ortho-carborane decorated with phenylamino groups effectively passivates the perovskite surface and essentially eliminates the non-radiative recombination loss across the perovskite/C₆₀ interface with high thermal stability. We further demonstrate the potential of carborane as an electron transport material, facilitating electron extraction while blocking holes from the interface. The resulting inverted perovskite solar cells deliver a power conversion efficiency of over 23% with a low non-radiative voltage loss of 110 mV, and retain >97% of the initial efficiency after 400 h of maximum power point tracking. Overall, the designed carborane based interlayer simultaneously enables passivation, electron-transport and hole-blocking and paves the way toward more efficient and stable perovskite solar cells.
Y1  - 2022
U6  - https://doi.org/10.1038/s41467-022-34203-x
SN  - 2041-1723
VL  - 13
IS  - 1
PB  - Springer Nature
CY  - London
ER  - 
TY  - JOUR
A1  - Former, C.
A1  - Wagner, H.
A1  - Richert, R.
A1  - Neher, Dieter
A1  - Müllen, K.
T1  - Orientation and dynamics of chainlike dipole arrays: Donor-acceptor-substituted oligophenylenevinylenes in a polymer matrix
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Samson, Stephanie
A1  - Rech, Jeromy
A1  - Perdigón-Toro, Lorena
A1  - Peng, Zhengxing
A1  - Shoaee, Safa
A1  - Ade, Harald
A1  - Neher, Dieter
A1  - Stolterfoht, Martin
A1  - You, Wei
T1  - Organic solar cells with large insensitivity to donor polymer molar mass across all acceptor classes
JF  - ACS applied polymer materials
N2  - Donor polymer number-average molar mass (M-n) has long been known to influence organic photovoltaic (OPV) performance via changes in both the polymer properties and the resulting bulk heterojunction morphology. The exact nature of these M-n effects varies from system to system, although there is generally some intermediate M-n that results in optimal performance. Interestingly, our earlier work with the difluorobenzotriazole (FTAZ)-based donor polymer, paired with either N2200 (polymer acceptor) or PC61BM (fullerene acceptor), PcBm demonstrated <10% variation in power conversion efficiency and a consistent morphology over a large span of M-n (30 kg/mol to over 100 kg/mol). Would such insensitivity to polymer M-n still hold true when prevailing small molecular acceptors were used with FTAZ? To answer this question, we explored the impact of FTAZ on OPVs with ITIC, a high-performance small-molecule fused-ring electron acceptor (FREA). By probing the photovoltaic characteristics of the resulting OPVs, we show that a similar FTAZ mn insensitivity is also found in the FTAZ:ITIC system. This study highlights a single-donor polymer which, when paired with an archetypal fullerene, polymer, and FREA, results in systems that are largely insensitive to donor M. Our results may have implications in polymer batch-to-batch reproducibility, in particular, relaxing the need for tight M-n control during synthesis.
KW  - polymer solar cells
KW  - conjugated polymers
KW  - fullerenes
KW  - fluorination
KW  - molecular weight
KW  - non-fullerene acceptors
KW  - power conversion efficiency
Y1  - 2020
U6  - https://doi.org/10.1021/acsapm.0c01041
SN  - 2637-6105
VL  - 2
IS  - 11
SP  - 5300
EP  - 5308
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Lieser, G.
A1  - Oda, Masao
A1  - Miteva, T.
A1  - Nothofer, Heinz-Georg
A1  - Scherf, Ullrich
A1  - Neher, Dieter
T1  - Ordering, graphoepitaxial orientation, and conformation of a polyfluorene derivative of the "hairy-rod" type on an oriented substrate of polyimide
Y1  - 2000
ER  - 
TY  - JOUR
A1  - Stiller, Burkhard
A1  - Karageorgiev, Peter
A1  - Geue, Thomas
A1  - Morawetz, Knut
A1  - Saphiannikova, Marina
A1  - Mechau, Norman
A1  - Neher, Dieter
T1  - Optically induced mass transport studied by scanning near-field optical- and atomic force microscopy
N2  - Some functionalised thin organic films show a very unusual property, namely the light induced material transport. This effect enables to generate three-dimensional structures on surfaces of azobenzene containing films only caused by special optical excitation. The physical mechanisms underlying this phenomenon have not yet been fully understood, and in addition, the dimensions of structures created in that way are macroscopic because of the optical techniques and the wavelength of the used light. In order to gain deeper insight into the physical fundamentals of this phenomenon and to open possibilities for applications it is necessary to create and study structures not only in a macroscopic but also in nanometer range. We first report about experiments to generate optically induced nano structures even down to 100 nm size. The optical stimulation was therefore made by a Scanning Near-field Optical Microscope (SNOM). Secondly, physical conditions inside optically generated surface relief gratings were studied by measuring mechanical properties with high lateral resolution via pulse force mode and force distance curves of an AFM
Y1  - 2004
SN  - 0204-3467
ER  - 
TY  - JOUR
A1  - Cimrová, V.
A1  - Neher, Dieter
A1  - Kostromine, S.
A1  - Bieringer, Thomas
T1  - Optical anisotropy in films of photoaddressable polymers
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Ilnytskyi, Jaroslav M.
A1  - Neher, Dieter
A1  - Saphiannikova, Marina
T1  - Opposite photo-induced deformations in azobenzene-containing polymers with different molecular architecture molecular dynamics study
JF  - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr
N2  - Photo-induced deformations in azobenzene-containing polymers (azo-polymers) are central to a number of applications, such as optical storage and fabrication of diffractive elements. The microscopic nature of the underlying opto-mechanical coupling is yet not clear. In this study, we address the experimental finding that the scenario of the effects depends on molecular architecture of the used azo-polymer. Typically, opposite deformations in respect to the direction of light polarization are observed for liquid crystalline and amorphous azo-polymers. In this study, we undertake molecular dynamics simulations of two different models that mimic these two types of azo-polymers. We employ hybrid force field modeling and consider only trans-isomers of azobenzene, represented as Gay-Berne sites. The effect of illumination on the orientation of the chromophores is considered on the level of orientational hole burning and emphasis is given to the resulting deformation of the polymer matrix. We reproduce deformations of opposite sign for the two models being considered here and discuss the relevant microscopic mechanisms in both cases.
KW  - amorphous state
KW  - light polarisation
KW  - liquid crystal polymers
KW  - molecular dynamics method
KW  - optical hole burning
KW  - photochemistry
Y1  - 2011
U6  - https://doi.org/10.1063/1.3614499
SN  - 0021-9606
VL  - 135
IS  - 4
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Poelking, Carl
A1  - Benduhn, Johannes
A1  - Spoltore, Donato
A1  - Schwarze, Martin
A1  - Roland, Steffen
A1  - Piersimoni, Fortunato
A1  - Neher, Dieter
A1  - Leo, Karl
A1  - Vandewal, Koen
A1  - Andrienko, Denis
T1  - Open-circuit voltage of organic solar cells
BT  - interfacial roughness makes the difference
JF  - Communications physics
N2  - Organic photovoltaics (PV) is an energy-harvesting technology that offers many advantages, such as flexibility, low weight and cost, as well as environmentally benign materials and manufacturing techniques. Despite growth of power conversion efficiencies to around 19 % in the last years, organic PVs still lag behind inorganic PV technologies, mainly due to high losses in open-circuit voltage. Understanding and improving open circuit voltage in organic solar cells is challenging, as it is controlled by the properties of a donor-acceptor interface where the optical excitations are separated into charge carriers. Here, we provide an electrostatic model of a rough donor-acceptor interface and test it experimentally on small molecule PV materials systems. The model provides concise relationships between the open-circuit voltage, photovoltaic gap, charge-transfer state energy, and interfacial morphology. In particular, we show that the electrostatic bias generated across the interface reduces the photovoltaic gap. This negative influence on open-circuit voltage can, however, be circumvented by adjusting the morphology of the donor-acceptor interface. 
Organic solar cells, despite their high power conversion efficiencies, suffer from open circuit voltage losses making them less appealing in terms of applications. Here, the authors, supported with experimental data on small molecule photovoltaic cells, relate open circuit voltage to photovoltaic gap, charge-transfer state energy, and donor-acceptor interfacial morphology.
Y1  - 2022
U6  - https://doi.org/10.1038/s42005-022-01084-x
SN  - 2399-3650
VL  - 5
IS  - 1
PB  - Nature portfolio
CY  - Berlin
ER  - 
TY  - JOUR
A1  - Fiesel, R.
A1  - Neher, Dieter
A1  - Scherf, Ullrich
T1  - On the solid state aggregation of chiral substituted poly(para-phenylene)s (PPPs)
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Caprioglio, Pietro
A1  - Stolterfoht, Martin
A1  - Wolff, Christian Michael
A1  - Unold, Thomas
A1  - Rech, Bernd
A1  - Albrecht, Steve
A1  - Neher, Dieter
T1  - On the relation between the open-circuit voltage and quasi-fermi level splitting in efficient perovskite solar cells
JF  - advanced energy materials
N2  - Today's perovskite solar cells (PSCs) are limited mainly by their open‐circuit voltage (VOC) due to nonradiative recombination. Therefore, a comprehensive understanding of the relevant recombination pathways is needed. Here, intensity‐dependent measurements of the quasi‐Fermi level splitting (QFLS) and of the VOC on the very same devices, including pin‐type PSCs with efficiencies above 20%, are performed. It is found that the QFLS in the perovskite lies significantly below its radiative limit for all intensities but also that the VOC is generally lower than the QFLS, violating one main assumption of the Shockley‐Queisser theory. This has far‐reaching implications for the applicability of some well‐established techniques, which use the VOC as a measure of the carrier densities in the absorber. By performing drift‐diffusion simulations, the intensity dependence of the QFLS, the QFLS‐VOC offset and the ideality factor are consistently explained by trap‐assisted recombination and energetic misalignment at the interfaces. Additionally, it is found that the saturation of the VOC at high intensities is caused by insufficient contact selectivity while heating effects are of minor importance. It is concluded that the analysis of the VOC does not provide reliable conclusions of the recombination pathways and that the knowledge of the QFLS‐VOC relation is of great importance.
KW  - electro-optical materials
KW  - perovskite solar cells
KW  - photovoltaic devices
KW  - thin films
Y1  - 2019
U6  - https://doi.org/10.1002/aenm.201901631
SN  - 1614-6832
SN  - 1614-6840
VL  - 9
IS  - 33
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Sandberg, Oskar J.
A1  - Kurpiers, Jona
A1  - Stolterfoht, Martin
A1  - Neher, Dieter
A1  - Meredith, Paul
A1  - Shoaee, Safa
A1  - Armin, Ardalan
T1  - On the question of the need for a built-in potential in Perovskite solar cells
JF  - Advanced materials interfaces
N2  - Perovskite semiconductors as the active materials in efficient solar cells exhibit free carrier diffusion lengths on the order of microns at low illumination fluxes and many hundreds of nanometers under 1 sun conditions. These lengthscales are significantly larger than typical junction thicknesses, and thus the carrier transport and charge collection should be expected to be diffusion controlled. A consensus along these lines is emerging in the field. However, the question as to whether the built-in potential plays any role is still of matter of some conjecture. This important question using phase-sensitive photocurrent measurements and theoretical device simulations based upon the drift-diffusion framework is addressed. In particular, the role of the built-in electric field and charge-selective transport layers in state-of-the-art p-i-n perovskite solar cells comparing experimental findings and simulation predictions is probed. It is found that while charge collection in the junction does not require a drift field per se, a built-in potential is still needed to avoid the formation of reverse electric fields inside the active layer, and to ensure efficient extraction through the charge transport layers.
KW  - built-in potential
KW  - charge collection
KW  - charge transport layers
KW  - perovskite solar cells
Y1  - 2020
U6  - https://doi.org/10.1002/admi.202000041
SN  - 2196-7350
VL  - 7
IS  - 10
PB  - Wiley
CY  - Hoboken
ER  - 
TY  - GEN
A1  - Pisoni, Stefano
A1  - Stolterfoht, Martin
A1  - Lockinger, Johannes
A1  - Moser, Thierry
A1  - Jiang, Yan
A1  - Caprioglio, Pietro
A1  - Neher, Dieter
A1  - Buecheler, Stephan
A1  - Tiwari, Ayodhya N.
T1  - On the origin of open-circuit voltage losses in flexible n-i-p perovskite solar cells
T2  - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
N2  - The possibility to manufacture perovskite solar cells (PSCs) at low temperatures paves the way to flexible and lightweight photovoltaic (PV) devices manufactured via high-throughput roll-to-roll processes. In order to achieve higher power conversion efficiencies, it is necessary to approach the radiative limit via suppression of non-radiative recombination losses. Herein, we performed a systematic voltage loss analysis for a typical low-temperature processed, flexible PSC in n-i-p configuration using vacuum deposited C-60 as electron transport layer (ETL) and two-step hybrid vacuum-solution deposition for CH3NH3PbI3 perovskite absorber. We identified the ETL/absorber interface as a bottleneck in relation to non-radiative recombination losses, the quasi-Fermi level splitting (QFLS) decreases from similar to 1.23 eV for the bare absorber, just similar to 90 meV below the radiative limit, to similar to 1.10 eV when C-60 is used as ETL. To effectively mitigate these voltage losses, we investigated different interfacial modifications via vacuum deposited interlayers (BCP, B4PyMPM, 3TPYMB, and LiF). An improvement in QFLS of similar to 30-40 meV is observed after interlayer deposition and confirmed by comparable improvements in the open-circuit voltage after implementation of these interfacial modifications in flexible PSCs. Further investigations on absorber/hole transport layer (HTL) interface point out the detrimental role of dopants in Spiro-OMeTAD film (widely employed HTL in the community) as recombination centers upon oxidation and light exposure. [GRAPHICS] .
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1110 
KW  - Perovskite solar cell
KW  - flexible
KW  - interface engineering
KW  - non-radiative recombination
KW  - quasi-Fermi level splitting
Y1  - 2021
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-459617
SN  - 1866-8372
IS  - 1110
ER  - 
TY  - JOUR
A1  - Pisoni, Stefano
A1  - Stolterfoht, Martin
A1  - Lockinger, Johannes
A1  - Moser, Thierry
A1  - Jiang, Yan
A1  - Caprioglio, Pietro
A1  - Neher, Dieter
A1  - Buecheler, Stephan
A1  - Tiwari, Ayodhya N.
T1  - On the origin of open-circuit voltage losses in flexible n-i-p perovskite solar cells
JF  - Science and technology of advanced materials : STAM
N2  - The possibility to manufacture perovskite solar cells (PSCs) at low temperatures paves the way to flexible and lightweight photovoltaic (PV) devices manufactured via high-throughput roll-to-roll processes. In order to achieve higher power conversion efficiencies, it is necessary to approach the radiative limit via suppression of non-radiative recombination losses. Herein, we performed a systematic voltage loss analysis for a typical low-temperature processed, flexible PSC in n-i-p configuration using vacuum deposited C-60 as electron transport layer (ETL) and two-step hybrid vacuum-solution deposition for CH3NH3PbI3 perovskite absorber. We identified the ETL/absorber interface as a bottleneck in relation to non-radiative recombination losses, the quasi-Fermi level splitting (QFLS) decreases from similar to 1.23 eV for the bare absorber, just similar to 90 meV below the radiative limit, to similar to 1.10 eV when C-60 is used as ETL. To effectively mitigate these voltage losses, we investigated different interfacial modifications via vacuum deposited interlayers (BCP, B4PyMPM, 3TPYMB, and LiF). An improvement in QFLS of similar to 30-40 meV is observed after interlayer deposition and confirmed by comparable improvements in the open-circuit voltage after implementation of these interfacial modifications in flexible PSCs. Further investigations on absorber/hole transport layer (HTL) interface point out the detrimental role of dopants in Spiro-OMeTAD film (widely employed HTL in the community) as recombination centers upon oxidation and light exposure. [GRAPHICS] .
KW  - Perovskite solar cell
KW  - flexible
KW  - interface engineering
KW  - non-radiative recombination
KW  - quasi-Fermi level splitting
Y1  - 2019
U6  - https://doi.org/10.1080/14686996.2019.1633952
SN  - 1468-6996
SN  - 1878-5514
VL  - 20
SP  - 786
EP  - 795
PB  - Taylor & Francis
CY  - Abingdon
ER  - 
TY  - JOUR
A1  - Sini, Gjergji
A1  - Schubert, Marcel
A1  - Risko, Chad
A1  - Roland, Steffen
A1  - Lee, Olivia P.
A1  - Chen, Zhihua
A1  - Richter, Thomas V.
A1  - Dolfen, Daniel
A1  - Coropceanu, Veaceslav
A1  - Ludwigs, Sabine
A1  - Scherf, Ullrich
A1  - Facchetti, Antonio
A1  - Frechet, Jean M. J.
A1  - Neher, Dieter
T1  - On the Molecular Origin of Charge Separation at the Donor-Acceptor Interface
JF  - Advanced energy materials
N2  - Fullerene-based acceptors have dominated organic solar cells for almost two decades. It is only within the last few years that alternative acceptors rival their dominance, introducing much more flexibility in the optoelectronic properties of these material blends. However, a fundamental physical understanding of the processes that drive charge separation at organic heterojunctions is still missing, but urgently needed to direct further material improvements. Here a combined experimental and theoretical approach is used to understand the intimate mechanisms by which molecular structure contributes to exciton dissociation, charge separation, and charge recombination at the donor-acceptor (D-A) interface. Model systems comprised of polythiophene-based donor and rylene diimide-based acceptor polymers are used and a detailed density functional theory (DFT) investigation is performed. The results point to the roles that geometric deformations and direct-contact intermolecular polarization play in establishing a driving force ( energy gradient) for the optoelectronic processes taking place at the interface. A substantial impact for this driving force is found to stem from polymer deformations at the interface, a finding that can clearly lead to new design approaches in the development of the next generation of conjugated polymers and small molecules.
KW  - donor-acceptor interfaces
KW  - energy gradients
KW  - geometrical deformations
KW  - nonfullerene acceptors
KW  - organic photovoltaics
KW  - photocurrent generation
KW  - polymer solar cells
Y1  - 2018
U6  - https://doi.org/10.1002/aenm.201702232
SN  - 1614-6832
SN  - 1614-6840
VL  - 8
IS  - 12
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Fritsch, Tobias
A1  - Kurpiers, Jona
A1  - Roland, Steffen
A1  - Tokmoldin, Nurlan
A1  - Shoaee, Safa
A1  - Ferron, Thomas
A1  - Collins, Brian A.
A1  - Janietz, Silvia
A1  - Vandewal, Koen
A1  - Neher, Dieter
T1  - On the interplay between CT and singlet exciton emission in organic solar cells with small driving force and its impact on voltage loss
JF  - Advanced energy materials
N2  - The interplay between free charge carriers, charge transfer (CT) states and singlet excitons (S-1) determines the recombination pathway and the resulting open circuit voltage (V-OC) of organic solar cells. 
By combining a well-aggregated low bandgap polymer with different blend ratios of the fullerenes PCBM and ICBA, the energy of the CT state (E-CT) is varied by 130 meV while leaving the S-1 energy of the polymer (ES1\[{E_{{{\rm{S}}_1}}}\]) unaffected. 
It is found that the polymer exciton dominates the radiative properties of the blend when ECT\[{E_{{\rm{CT}}}}\] approaches ES1\[{E_{{{\rm{S}}_1}}}\], while the V-OC remains limited by the non-radiative decay of the CT state. 
It is concluded that an increasing strength of the exciton in the optical spectra of organic solar cells will generally decrease the non-radiative voltage loss because it lowers the radiative V-OC limit (V-OC,V-rad), but not because it is more emissive. 
The analysis further suggests that electronic coupling between the CT state and the S-1 will not improve the V-OC, but rather reduce the V-OC,V-rad. 
It is anticipated that only at very low CT state absorption combined with a fairly high CT radiative efficiency the solar cell benefit from the radiative properties of the singlet excitons.
KW  - external quantum efficiency
KW  - organic photovoltaics
KW  - ternary blends
KW  - voltage losses
Y1  - 2022
U6  - https://doi.org/10.1002/aenm.202200641
SN  - 1614-6832
SN  - 1614-6840
VL  - 12
IS  - 31
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Albrecht, Steve
A1  - Schindler, Wolfram
A1  - Kurpiers, Jona
A1  - Kniepert, Juliane
A1  - Blakesley, James C.
A1  - Dumsch, Ines
A1  - Allard, Sybille
A1  - Fostiropoulos, Konstantinos
A1  - Scherf, Ullrich
A1  - Neher, Dieter
T1  - On the field dependence of free charge carrier generation and recombination in blends of PCPDTBT/PC70BM influence of solvent additives
JF  - The journal of physical chemistry letters
N2  - We have applied time-delayed collection field (TDCF) and charge extraction by linearly increasing voltage (CELIV) to investigate the photogeneration, transport, and recombination of charge carriers in blends composed of PCPDTBT/PC70BM processed with and without the solvent additive diiodooctane. The results suggest that the solvent additive has severe impacts on the elementary processes involved in the photon to collected electron conversion in these blends. First, a pronounced field dependence of the free carrier generation is found for both blends, where the field dependence is stronger without the additive. Second, the fate of charge carriers in both blends can be described with a rather high bimolecular recombination coefficients, which increase with decreasing internal field. Third, the mobility is three to four times higher with the additive. Both blends show a negative field dependence of mobility, which we suggest to cause bias-dependent recombination coefficients.
Y1  - 2012
U6  - https://doi.org/10.1021/jz3000849
SN  - 1948-7185
VL  - 3
IS  - 5
SP  - 640
EP  - 645
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Albrecht, Steve
A1  - Vandewal, Koen
A1  - Tumbleston, John R.
A1  - Fischer, Florian S. U.
A1  - Douglas, Jessica D.
A1  - Frechet, Jean M. J.
A1  - Ludwigs, Sabine
A1  - Ade, Harald W.
A1  - Salleo, Alberto
A1  - Neher, Dieter
T1  - On the efficiency of charge transfer state splitting in polymer: Fullerene solar cells
JF  - Advanced materials
KW  - organic solar cells
KW  - charge generation
KW  - geminate recombination
KW  - charge transfer states
KW  - driving force
KW  - excess energy
KW  - morphology
KW  - spectroelectrochemistry
Y1  - 2014
U6  - https://doi.org/10.1002/adma.201305283
SN  - 0935-9648
SN  - 1521-4095
VL  - 26
IS  - 16
SP  - 2533
EP  - 2539
PB  - Wiley-VCH
CY  - Weinheim
ER  -