TY - JOUR A1 - Jošt, Marko A1 - Albrecht, Steve A1 - Kegelmann, Lukas A1 - Wolff, Christian Michael A1 - Lang, Felix A1 - Lipovšek, Benjamin A1 - Krč, Janez A1 - Korte, Lars A1 - Neher, Dieter A1 - Rech, Bernd A1 - Topič, Marko T1 - Efficient light management by textured nanoimprinted layers for perovskite solar cells JF - ACS photonics N2 - Inorganic-organic perovskites like methylammonium-lead-iodide have proven to be an effective class of 17 materials for fabricating efficient solar cells. To improve their performance, light management techniques using textured surfaces, similar to those used in established solar cell technologies, should be considered. Here, we apply a light management foil created by UV nanoimprint lithography on the glass side of an inverted (p-i-n) perovskite solar cell with 16.3% efficiency. The obtained 1 mA cm(-2) increase in the short-circuit current density translates to a relative improvement in cell performance of 5%, which results in a power conversion efficiency of 17.1%. Optical 3D simulations based on experimentally obtained parameters were used to support the experimental findings. A good match between the simulated and experimental data was obtained, validating the model. Optical simulations reveal that the main improvement in device performance is due to a reduction in total reflection and that relative improvement in the short-circuit current density of up to 10% is possible for large-area devices. Therefore, our results present the potential of light management foils for improving the device performance of perovskite solar cells and pave the way for further use of optical simulations in the field of perovskite solar cells. KW - perovskite solar cells KW - antireflection KW - light management KW - UV nanoimprint lithography KW - optical simulations Y1 - 2017 U6 - https://doi.org/10.1021/acsphotonics.7b00138 SN - 2330-4022 VL - 4 SP - 1232 EP - 1239 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Yang, Xiao Hui A1 - Jaiser, Frank A1 - Stiller, Burkhard A1 - Neher, Dieter A1 - Galbrecht, Frank A1 - Scherf, Ullrich T1 - Efficient polymer electrophosphoreseent devices with interfacial layers JF - Advanced functional materials N2 - It is shown that several polymers can form insoluble interfacial layers on a poly (ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) layer after annealing of the double-layer structure. The thickness of the interlayer is dependent on the characteristics of the underlying PEDOT.PSS and the molecular weight of the polymers. It is further shown that the electronic structures of the interlayer polymers have a significant effect on the properties of red-light-emitting polymer-based electrophosphorescent devices. Upon increasing the highest occupied molecular orbital and lowest unoccupied molecular orbital positions, a significant increase in current density and device efficiency is observed. This is attributed to efficient blocking of electrons in combination with direct injection of holes from the interlayer to the phosphorescent dye. Upon proper choice of the interlayer polymer, efficient red, polymer-based electrophosphorescent devices with a peak luminance efficiency of 5.5 cd A(-1) (external quantum efficiency = 6 %) and a maximum power-conversion efficiency of 5 Im W-1 can be realized. Y1 - 2006 U6 - https://doi.org/10.1002/adfm.200500834 SN - 1616-301X SN - 1616-3028 VL - 16 IS - 16 SP - 2156 EP - 2162 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Kietzke, Thomas A1 - Horhold, H. H. A1 - Neher, Dieter T1 - Efficient polymer solar cells based on M3EH-PPV N2 - We report on polymer blend solar cells with an external quantum efficiency of more than 30% and a hi-h overall energy conversion efficiency (ECE) under white light illumination (100 mW/cm(2)) Of Lip to 1.7% using a blend of M3EH- PPV (poly [2,5-dimethoxy-1,4-phenylene-1,2-ethenylene-2-methoxy-5(2-ethylhexyloxy)-(1,4-pheiiylene-1,2-ethenylene)]) and CN-ether-PPV (poly[oxa-1,4-phenylene-1,2(1-cyano)ethenylene-2,5-dioctyloxy-1,4-phenylene-1,2-(2-cyano)ethellyiene-1,4- phenylene]). We attribute these high efficiencies to the formation of a vertically composition graded structure during spin coating Photoluminescence measurements performed on the blend layers indicated the formation of exciplexes between both types of polymers, which we propose to be one factor preventing even higher efficiencies Y1 - 2005 ER - TY - JOUR A1 - Al-Sa'di, Mahmoud A1 - Jaiser, Frank A1 - Bagnich, Sergey A. A1 - Unger, Thomas A1 - Blakesley, James C. A1 - Wilke, Andreas A1 - Neher, Dieter T1 - Electrical and optical simulations of a polymer-based phosphorescent organic light-emitting diode with high efficiency JF - Journal of polymer science : B, Polymer physics N2 - A comprehensive numerical device simulation of the electrical and optical characteristics accompanied with experimental measurements of a new highly efficient system for polymer-based light-emitting diodes doped with phosphorescent dyes is presented. The system under investigation comprises an electron transporter attached to a polymer backbone blended with an electronically inert small molecule and an iridium-based green phosphorescent dye which serves as both emitter and hole transporter. The device simulation combines an electrical and an optical model. Based on the known highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels of all components as well as the measured electrical and optical characteristics of the devices, we model the emissive layer as an effective medium using the dye's HOMO as hole transport level and the polymer LUMO as electron transport level. By fine-tuning the injection barriers at the electron and hole-injecting contact, respectively, in simulated devices, unipolar device characteristics were fitted to the experimental data. Simulations using the so-obtained set of parameters yielded very good agreement to the measured currentvoltage, luminancevoltage characteristics, and the emission profile of entire bipolar light-emitting diodes, without additional fitting parameters. The simulation was used to gain insight into the physical processes and the mechanisms governing the efficiency of the organic light-emitting diode, including the position and extent of the recombination zone, carrier concentration profiles, and field distribution inside the device. The simulations show that the device is severely limited by hole injection, and that a reduction of the hole-injection barrier would improve the device efficiency by almost 50%. KW - conjugated polymers KW - high performance polymers KW - organic electronics KW - organic light-emitting diode KW - simulations KW - TCAD Y1 - 2012 U6 - https://doi.org/10.1002/polb.23158 SN - 0887-6266 VL - 50 IS - 22 SP - 1567 EP - 1576 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Ullbrich, Sascha A1 - Benduhn, Johannes A1 - Jia, Xiangkun A1 - Nikolis, Vasileios C. A1 - Tvingstedt, Kristofer A1 - Piersimoni, Fortunato A1 - Roland, Steffen A1 - Liu, Yuan A1 - Wu, Jinhan A1 - Fischer, Axel A1 - Neher, Dieter A1 - Reineke, Sebastian A1 - Spoltore, Donato A1 - Vandewal, Koen T1 - Emissive and charge-generating donor-acceptor interfaces for organic optoelectronics with low voltage losses JF - Nature materials N2 - Intermolecular charge-transfer states at the interface between electron donating (D) and accepting (A) materials are crucial for the operation of organic solar cells but can also be exploited for organic light-emitting diodes(1,2). Non-radiative charge-transfer state decay is dominant in state-of-the-art D-A-based organic solar cells and is responsible for large voltage losses and relatively low power-conversion efficiencies as well as electroluminescence external quantum yields in the 0.01-0.0001% range(3,4). In contrast, the electroluminescence external quantum yield reaches up to 16% in D-A-based organic light-emitting diodes(5-7). Here, we show that proper control of charge-transfer state properties allows simultaneous occurrence of a high photovoltaic and emission quantum yield within a single, visible-light-emitting D-A system. This leads to ultralow-emission turn-on voltages as well as significantly reduced voltage losses upon solar illumination. These results unify the description of the electro-optical properties of charge-transfer states in organic optoelectronic devices and foster the use of organic D-A blends in energy conversion applications involving visible and ultraviolet photons(8-11). KW - Electronics, photonics and device physics KW - Optoelectronic devices and components KW - Photonic devices KW - Solar energy and photovoltaic technology Y1 - 2019 U6 - https://doi.org/10.1038/s41563-019-0324-5 SN - 1476-1122 SN - 1476-4660 VL - 18 IS - 5 SP - 459 EP - 464 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Bagnich, Sergey A. A1 - Im, C. A1 - Bassler, H. A1 - Neher, Dieter A1 - Scherf, Ullrich T1 - Energy transfer in a ladder-type methyl-poly(para-phenylene) doped by Pt(II)octaethylporphyrin N2 - The luminescence of a ladder-type methyl-poly(para-phenylene) (MeLPPP) doped by platinum-porphyrin dye PtOEP covering the concentration 10(-3) to 5% by weight has been measured employing cw and transient techniques. Upon excitating into the range of absorption of the host strong phosphorescence of the dopant is observed. Possible ways of populating of the dopant triplet state are considered. It is shown that the main channel is singlet-singlet energy transfer among chromophor groups of the polymer followed by Forster-type transfer to the guest and subsequent intersystem crossing. (C) 2003 Elsevier B.V. All rights reserved Y1 - 2004 SN - 0301-0104 ER - TY - JOUR A1 - Collado-Fregoso, Elisa A1 - Pugliese, Silvina N. A1 - Wojcik, Mariusz A1 - Benduhn, Johannes A1 - Bar-Or, Eyal A1 - Perdigón-Toro, Lorena A1 - Hörmann, Ulrich A1 - Spoltore, Donato A1 - Vandewal, Koen A1 - Hodgkiss, Justin M. A1 - Neher, Dieter T1 - Energy-gap law for photocurrent generation in fullerene-based organic solar cells BT - the case of low-donor-content blends JF - Journal of the American Chemical Society N2 - The involvement of charge-transfer (CT) states in the photogeneration and recombination of charge carriers has been an important focus of study within the organic photovoltaic community. In this work, we investigate the molecular factors determining the mechanism of photocurrent generation in low-donor-content organic solar cells, where the active layer is composed of vacuum-deposited C-60 and small amounts of organic donor molecules. We find a pronounced decline of all photovoltaic parameters with decreasing CT state energy. Using a combination of steady-state photocurrent measurements and time-delayed collection field experiments, we demonstrate that the power conversion efficiency, and more specifically, the fill factor of these devices, is mainly determined by the bias dependence of photocurrent generation. By combining these findings with the results from ultrafast transient absorption spectroscopy, we show that blends with small CT energies perform poorly because of an increased nonradiative CT state decay rate and that this decay obeys an energy-gap law. Our work challenges the common view that a large energy offset at the heterojunction and/or the presence of fullerene clusters guarantee efficient CT dissociation and rather indicates that charge generation benefits from high CT state energies through a slower decay to the ground state. Y1 - 2019 U6 - https://doi.org/10.1021/jacs.8b09820 SN - 0002-7863 VL - 141 IS - 6 SP - 2329 EP - 2341 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Pranav, Manasi A1 - Benduhn, Johannes A1 - Nyman, Mathias A1 - Hosseini, Seyed Mehrdad A1 - Kublitski, Jonas A1 - Shoaee, Safa A1 - Neher, Dieter A1 - Leo, Karl A1 - Spoltore, Donato T1 - Enhanced charge selectivity via anodic-C60 layer reduces nonradiative losses in organic solar cells JF - ACS applied materials & interfaces N2 - Interfacial layers in conjunction with suitable charge-transport layers can significantly improve the performance of optoelectronic devices by facilitating efficient charge carrier injection and extraction. This work uses a neat C-60 interlayer on the anode to experimentally reveal that surface recombination is a significant contributor to nonradiative recombination losses in organic solar cells. These losses are shown to proportionally increase with the extent of contact between donor molecules in the photoactive layer and a molybdenum oxide (MoO3) hole extraction layer, proven by calculating voltage losses in low- and high-donor-content bulk heterojunction device architectures. Using a novel in-device determination of the built-in voltage, the suppression of surface recombination, due to the insertion of a thin anodic-C-60 interlayer on MoO3, is attributed to an enhanced built-in potential. The increased built-in voltage reduces the presence of minority charge carriers at the electrodes-a new perspective on the principle of selective charge extraction layers. The benefit to device efficiency is limited by a critical interlayer thickness, which depends on the donor material in bilayer devices. Given the high popularity of MoO3 as an efficient hole extraction and injection layer and the increasingly popular discussion on interfacial phenomena in organic optoelectronic devices, these findings are relevant to and address different branches of organic electronics, providing insights for future device design. KW - nonradiative losses KW - molybdenum oxide KW - organic solar cells KW - interfacial layers KW - charge selectivity Y1 - 2021 U6 - https://doi.org/10.1021/acsami.1c00049 SN - 1944-8244 SN - 1944-8252 VL - 13 IS - 10 SP - 12603 EP - 12609 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Roland, Steffen A1 - Kniepert, Juliane A1 - Love, John A. A1 - Negi, Vikas A1 - Liu, Feilong A1 - Bobbert, Peter A1 - Melianas, Armantas A1 - Kemerink, Martijn A1 - Hofacker, Andreas A1 - Neher, Dieter T1 - Equilibrated Charge Carrier Populations Govern Steady-State Nongeminate Recombination in Disordered Organic Solar Cells JF - The journal of physical chemistry letters N2 - We employed bias-assisted charge extraction techniques to investigate the transient and steady-state recombination of photogenerated charge carriers in complete devices of a disordered polymer-fullerene blend. Charge recombination is shown to be dispersive, with a significant slowdown of the recombination rate over time, consistent with the results from kinetic Monte Carlo simulations. Surprisingly, our experiments reveal little to no contributions from early time recombination of nonequilibrated charge carriers to the steady-state recombination properties. We conclude that energetic relaxation of photogenerated carriers outpaces any significant nongeminate recombination under application-relevant illumination conditions. With equilibrated charges dominating the steady-state recombination, quasi-equilibrium concepts appear suited for describing the open-circuit voltage of organic solar cells despite pronounced energetic disorder. Y1 - 2019 U6 - https://doi.org/10.1021/acs.jpclett.9b00516 SN - 1948-7185 VL - 10 IS - 6 SP - 1374 EP - 1381 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Bagnich, Sergey A. A1 - Bassler, H. A1 - Neher, Dieter T1 - Exciton dynamics in ladder-type methyl-poly(para-phenylene) doped with phosphorescent dyes N2 - The luminescence of a ladder-type methyl-poly(para-phenylene) (MeLPPP) doped with platinum-porphyrin dye PtOEP covering the concentration 10(-3)-5% by weight has been measured employing cw and transient techniques. Upon excitation into the range of absorption of the host, strong phosphorescence of the dopant is observed. Possible ways of populating the dopant triplet state are considered. (c) 2004 Elsevier B.V. All rights reserved Y1 - 2005 SN - 0022-2313 ER -