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  - Chen, Zupeng
A1  - Savateev, Aleksandr
A1  - Pronkin, Sergey
A1  - Papaefthimiou, Vasiliki
A1  - Wolff, Christian Michael
A1  - Willinger, Marc Georg
A1  - Willinger, Elena
A1  - Neher, Dieter
A1  - Antonietti, Markus
A1  - Dontsova, Dariya
T1  - "The Easier the Better" Preparation of Efficient Photocatalysts-Metastable Poly(heptazine imide) Salts
JF  - Advanced materials
N2  - Cost-efficient, visible-light-driven hydrogen production from water is an attractive potential source of clean, sustainable fuel. Here, it is shown that thermal solid state reactions of traditional carbon nitride precursors (cyanamide, melamine) with NaCl, KCl, or CsCl are a cheap and straightforward way to prepare poly(heptazine imide) alkali metal salts, whose thermodynamic stability decreases upon the increase of the metal atom size. The chemical structure of the prepared salts is confirmed by the results of X-ray photoelectron and infrared spectroscopies, powder X-ray diffraction and electron microscopy studies, and, in the case of sodium poly(heptazine imide), additionally by atomic pair distribution function analysis and 2D powder X-ray diffraction pattern simulations. In contrast, reactions with LiCl yield thermodynamically stable poly(triazine imides). Owing to the metastability and high structural order, the obtained heptazine imide salts are found to be highly active photo-catalysts in Rhodamine B and 4-chlorophenol degradation, and Pt-assisted sacrificial water reduction reactions under visible light irradiation. The measured hydrogen evolution rates are up to four times higher than those provided by a benchmark photocatalyst, mesoporous graphitic carbon nitride. Moreover, the products are able to photocatalytically reduce water with considerable reaction rates, even when glycerol is used as a sacrificial hole scavenger.
KW  - carbon nitride
KW  - glycerol oxidation
KW  - mesocrystals
KW  - poly(heptazine imide)
KW  - water reduction reactions
Y1  - 2017
U6  - https://doi.org/10.1002/adma.201700555
SN  - 0935-9648
SN  - 1521-4095
VL  - 29
SP  - 21800
EP  - 21806
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Caprioglio, Pietro
A1  - Zu, Fengshuo
A1  - Wolff, Christian Michael
A1  - Prieto, Jose A. Marquez
A1  - Stolterfoht, Martin
A1  - Becker, Pascal
A1  - Koch, Norbert
A1  - Unold, Thomas
A1  - Rech, Bernd
A1  - Albrecht, Steve
A1  - Neher, Dieter
T1  - High open circuit voltages in pin-type perovskite solar cells through strontium addition
JF  - Sustainable Energy & Fuels
N2  - The incorporation of even small amounts of strontium (Sr) into lead-base hybrid quadruple cation perovskite solar cells results in a systematic increase of the open circuit voltage (V-oc) in pin-type perovskite solar cells. We demonstrate via absolute and transient photoluminescence (PL) experiments how the incorporation of Sr significantly reduces the non-radiative recombination losses in the neat perovskite layer. We show that Sr segregates at the perovskite surface, where it induces important changes of morphology and energetics. Notably, the Sr-enriched surface exhibits a wider band gap and a more n-type character, accompanied with significantly stronger surface band bending. As a result, we observe a significant increase of the quasi-Fermi level splitting in the neat perovskite by reduced surface recombination and more importantly, a strong reduction of losses attributed to non-radiative recombination at the interface to the C-60 electron-transporting layer. The resulting solar cells exhibited a V-oc of 1.18 V, which could be further improved to nearly 1.23 V through addition of a thin polymer interlayer, reducing the non-radiative voltage loss to only 110 meV. Our work shows that simply adding a small amount of Sr to the precursor solutions induces a beneficial surface modification in the perovskite, without requiring any post treatment, resulting in high efficiency solar cells with power conversion efficiency (PCE) up to 20.3%. Our results demonstrate very high V-oc values and efficiencies in Sr-containing quadruple cation perovskite pin-type solar cells and highlight the imperative importance of addressing and minimizing the recombination losses at the interface between perovskite and charge transporting layer.
Y1  - 2019
U6  - https://doi.org/10.1039/c8se00509e
SN  - 2398-4902
VL  - 3
IS  - 2
SP  - 550
EP  - 563
PB  - Royal Society of Chemistry
CY  - Cambridge
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  - 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  - Braunger, Steffen
A1  - Mundt, Laura E.
A1  - Wolff, Christian Michael
A1  - Mews, Mathias
A1  - Rehermann, Carolin
A1  - Jost, Marko
A1  - Tejada, Alvaro
A1  - Eisenhauer, David
A1  - Becker, Christiane
A1  - Andres Guerra, Jorge
A1  - Unger, Eva
A1  - Korte, Lars
A1  - Neher, Dieter
A1  - Schubert, Martin C.
A1  - Rech, Bernd
A1  - Albrecht, Steve
T1  - Cs(x)FA(1-x)Pb(l(1-y)Br(y))(3) Perovskite Compositions
BT  - the Appearance of Wrinkled Morphology and its Impact on Solar Cell Performance
JF  - The journal of physical chemistry : C, Nanomaterials and interfaces
N2  - We report on the formation of wrinkle-patterned surface morphologies in cesium formamidinium-based Cs(x)FA(1-y)Pb(I1-yBry)(3) perovskite compositions with x = 0-0.3 and y = 0-0.3 under various spin-coating conditions. By varying the Cs and Br contents, the perovskite precursor solution concentration and the spin-coating procedure, the occurrence and characteristics of the wrinkle-shaped morphology can be tailored systematically. Cs(0.17)FA(0.83)Pb(I0.83Br0.17)(3) perovskite layers were analyzed regarding their surface roughness, microscopic structure, local and overall composition, and optoelectronic properties. Application of these films in p-i-n perovskite solar cells (PSCs) with indium-doped tin oxide/NiOx/perovskite/C-60/bathocuproine/Cu architecture resulted in up to 15.3 and 17.0% power conversion efficiency for the flat and wrinkled morphology, respectively. Interestingly, we find slightly red-shifted photoluminescence (PL) peaks for wrinkled areas and we are able to directly correlate surface topography with PL peak mapping. This is attributed to differences in the local grain size, whereas there is no indication for compositional demixing in the films. We show that the perovskite composition, crystallization kinetics, and layer thickness strongly influence the formation of wrinkles which is proposed to be related to the release of compressive strain during perovskite crystallization. Our work helps us to better understand film formation and to further improve the efficiency of PSCs with widely used mixed-perovskite compositions.
Y1  - 2018
U6  - https://doi.org/10.1021/acs.jpcc.8b06459
SN  - 1932-7447
SN  - 1932-7455
VL  - 122
IS  - 30
SP  - 17123
EP  - 17135
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Blakesley, James C.
A1  - Schubert, Marcel
A1  - Steyrleuthner, Robert
A1  - Chen, Zhihua
A1  - Facchetti, Antonio
A1  - Neher, Dieter
T1  - Time-of-flight measurements and vertical transport in a high electron-mobility polymer
JF  - Applied physics letters
N2  - We investigate charge transport in a high-electron mobility polymer, poly(N, N-bis 2-octyldodecyl-naphthalene-1,4,5,8-bis dicarboximide-2,6-diyl-alt-5,5-2,2-bithiophene) [P(NDI2OD-T2), Polyera ActivInk (TM) N2200]. Time-of-flight measurements reveal electron mobilities approaching those measured in field-effect transistors, the highest ever recorded in a conjugated polymer using this technique. The modest temperature dependence and weak dispersion of the transients indicate low energetic disorder in this material. Steady-state electron-only current measurements reveal a barrier to injection of about 300 meV. We propose that this barrier is located within the P(NDI2OD-T2) film and arises from molecular orientation effects.
Y1  - 2011
U6  - https://doi.org/10.1063/1.3657827
SN  - 0003-6951
VL  - 99
IS  - 18
PB  - American Institute of Physics
CY  - Melville
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  - Bittner, Reinhard
A1  - Däubler, Thomas Karl
A1  - Neher, Dieter
A1  - Meerholz, Klaus
T1  - Influence of the glass-transition and the chromophore content on the steady-state performance of PVK-based photorefractive polymers
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Benduhn, Johannes
A1  - Tvingstedt, Kristofer
A1  - Piersimoni, Fortunato
A1  - Ullbrich, Sascha
A1  - Fan, Yeli
A1  - Tropiano, Manuel
A1  - McGarry, Kathryn A.
A1  - Zeika, Olaf
A1  - Riede, Moritz K.
A1  - Douglas, Christopher J.
A1  - Barlow, Stephen
A1  - Marder, Seth R.
A1  - Neher, Dieter
A1  - Spoltore, Donato
A1  - Vandewal, Koen
T1  - Intrinsic non-radiative voltage losses in fullerene-based organic solar cells
JF  - Nature Energy
N2  - Organic solar cells demonstrate external quantum efficiencies and fill factors approaching those of conventional photovoltaic technologies. However, as compared with the optical gap of the absorber materials, their open-circuit voltage is much lower, largely due to the presence of significant non-radiative recombination. Here, we study a large data set of published and new material combinations and find that non-radiative voltage losses decrease with increasing charge-transfer-state energies. This observation is explained by considering non-radiative charge-transfer-state decay as electron transfer in the Marcus inverted regime, being facilitated by a common skeletal molecular vibrational mode. Our results suggest an intrinsic link between non-radiative voltage losses and electron-vibration coupling, indicating that these losses are unavoidable. Accordingly, the theoretical upper limit for the power conversion efficiency of single-junction organic solar cells would be reduced to about 25.5% and the optimal optical gap increases to (1.45-1.65) eV, that is, (0.2-0.3) eV higher than for technologies with minimized non-radiative voltage losses.
Y1  - 2017
U6  - https://doi.org/10.1038/nenergy.2017.53
SN  - 2058-7546
VL  - 2
PB  - Nature Publ. Group
CY  - London
ER  -