TY - JOUR A1 - Fang, Lijia A1 - Holzmueller, Felix A1 - Matulaitis, Tomas A1 - Baasner, Anne A1 - Hauenstein, Christoph A1 - Benduhn, Johannes A1 - Schwarze, Martin A1 - Petrich, Annett A1 - Piersimoni, Fortunato A1 - Scholz, Reinhard A1 - Zeika, Olaf A1 - Koerner, Christian A1 - Neher, Dieter A1 - Vandewal, Koen A1 - Leo, Karl T1 - Fluorine-containing low-energy-gap organic dyes with low voltage losses for organic solar cells JF - Synthetic metals : the journal of electronic polymers and electronic molecular materials N2 - Fluorine-containing donor molecules TFTF, CNTF and PRTF are designed and isomer selectively synthesized for application in vacuum-deposited organic solar cells. These molecules comprise a donor acceptor molecular architecture incorporating thiophene and benzothiadiazole derivatives as the electron-donating and electron-withdrawing moieties, respectively. As opposed to previously reported materials from this class, PRTF can be purified by vacuum sublimation at moderate to high yields because of its higher volatility and better stabilization due to a stronger intramolecular hydrogen bond, as compared to TFTF and CNTF. The UV-vis absorption spectra of the three donors show an intense broadband absorption between 500 nm and 800 nm with, similar positions of their frontier energy levels. The photophysical properties of the three donor molecules are thoroughly tested and optimized in bulk heterojunction solar cells with C-60 as acceptor. PRTF shows the best performance, yielding power conversion efficiencies of up to 3.8%. Moreover, the voltage loss for the PRTF device due to the non radiative recombination of free charge carriers is exceptionally low (0.26 V) as compared to typical values for organic solar cells (>0.34V). (C) 2016 Published by Elsevier B.V. KW - (Z)-isomer KW - Donor materials KW - CH center dot center dot center dot F hydrogen bonds KW - Sublimation with good yield KW - Low voltage losses Y1 - 2016 U6 - https://doi.org/10.1016/j.synthmet.2016.10.025 SN - 0379-6779 VL - 222 SP - 232 EP - 239 PB - Elsevier CY - Lausanne ER - TY - JOUR A1 - Li, Tian-yi A1 - Benduhn, Johannes A1 - Li, Yue A1 - Jaiser, Frank A1 - Spoltore, Donato A1 - Zeika, Olaf A1 - Ma, Zaifei A1 - Neher, Dieter A1 - Vandewal, Koen A1 - Leo, Karl T1 - Boron dipyrromethene (BODIPY) with meso-perfluorinated alkyl substituents as near infrared donors in organic solar cells JF - Journal of materials chemistry : A, Materials for energy and sustainability N2 - Three furan-fused BODIPYs were synthesized with perfluorinated methyl, ethyl and n-propyl groups on the meso-carbon. They were obtained with high yields by reacting the furan-fused 2-carboxylpyrrole in corresponding perfluorinated acid and anhydride. With the increase in perfluorinated alkyl chain length, the molecular packing in the single crystal is influenced, showing increasing stacking distance and decreasing slope angle. All the BODIPYs were characterized as intense absorbers in near infrared region in solid state, peaking at similar to 800 nm with absorption coefficient of over 280 000 cm(-1). Facilitated by high thermal stability, the furan-fused BODIPYs were employed in vacuum-deposited organic solar cells as electron donors. All devices exhibit PCE over 6.0% with the EQE maximum reaching 70% at similar to 790 nm. The chemical modification of the BODIPY donors have certain influence on the active layer morphology, and the highest PCE of 6.4% was obtained with a notably high jsc of 13.6 mA cm(-2). Sensitive EQE and electroluminance studies indicated that the energy losses generated by the formation of a charge transfer state and the radiative recombination at the donor-acceptor interface were comparable in the range of 0.14-0.19 V, while non-radiative recombination energy loss of 0.38 V was the main energy loss route resulting in the moderate V-oc of 0.76 V. Y1 - 2018 U6 - https://doi.org/10.1039/c8ta06261g SN - 2050-7488 SN - 2050-7496 VL - 6 IS - 38 SP - 18583 EP - 18591 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Schwarze, Martin A1 - Schellhammer, Karl Sebastian A1 - Ortstein, Katrin A1 - Benduhn, Johannes A1 - Gaul, Christopher A1 - Hinderhofer, Alexander A1 - Perdigon-Toro, Lorena A1 - Scholz, Reinhard A1 - Kublitski, Jonas A1 - Roland, Steffen A1 - Lau, Matthias A1 - Poelking, Carl A1 - Andrienko, Denis A1 - Cuniberti, Gianaurelio A1 - Schreiber, Frank A1 - Neher, Dieter A1 - Vandewal, Koen A1 - Ortmann, Frank A1 - Leo, Karl T1 - Impact of molecular quadrupole moments on the energy levels at organic heterojunctions JF - Nature Communications N2 - The functionality of organic semiconductor devices crucially depends on molecular energies, namely the ionisation energy and the electron affinity. Ionisation energy and electron affinity values of thin films are, however, sensitive to film morphology and composition, making their prediction challenging. In a combined experimental and simulation study on zinc-phthalocyanine and its fluorinated derivatives, we show that changes in ionisation energy as a function of molecular orientation in neat films or mixing ratio in blends are proportional to the molecular quadrupole component along the p-p-stacking direction. We apply these findings to organic solar cells and demonstrate how the electrostatic interactions can be tuned to optimise the energy of the charge-transfer state at the donor-acceptor interface and the dissociation barrier for free charge carrier generation. The confirmation of the correlation between interfacial energies and quadrupole moments for other materials indicates its relevance for small molecules and polymers. Y1 - 2019 U6 - https://doi.org/10.1038/s41467-019-10435-2 SN - 2041-1723 VL - 10 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Li, Tian-yi A1 - Benduhn, Johannes A1 - Qiao, Zhi A1 - Liu, Yuan A1 - Li, Yue A1 - Shivhare, Rishi A1 - Jaiser, Frank A1 - Wang, Pei A1 - Ma, Jie A1 - Zeika, Olaf A1 - Neher, Dieter A1 - Mannsfeld, Stefan C. B. A1 - Ma, Zaifei A1 - Vandewal, Koen A1 - Leo, Karl T1 - Effect of H- and J-Aggregation on the Photophysical and Voltage Loss of Boron Dipyrromethene Small Molecules in Vacuum-Deposited Organic Solar Cells JF - The journal of physical chemistry letters N2 - An understanding of the factors limiting the open-circuit voltage (V-oc) and related photon energy loss mechanisms is critical to increase the power conversion efficiency (PCE) of small-molecule organic solar cells (OSCs), especially those with near-infrared (NIR) absorbers. In this work, two NIR boron dipyrromethene (BODIPY) molecules are characterized for application in planar (PHJ) and bulk (BHJ) heterojunction OSCs. When two H atoms are substituted by F atoms on the peripheral phenyl rings of the molecules, the molecular aggregation type in the thin film changes from the H-type to J-type. For PHJ devices, the nonradiative voltage loss of 0.35 V in the J-aggregated BODIPY is lower than that of 0.49 V in the H-aggregated device. In BHJ devices with a nonradiative voltage loss of 0.35 V, a PCE of 5.5% is achieved with an external quantum efficiency (EQE) maximum of 68% at 700 nm. Y1 - 2019 U6 - https://doi.org/10.1021/acs.jpclett.9b01222 SN - 1948-7185 VL - 10 IS - 11 SP - 2684 EP - 2691 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 - 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 -