TY  - JOUR
A1  - Würfel, Uli
A1  - Neher, Dieter
A1  - Spies, Annika
A1  - Albrecht, Steve
T1  - Impact of charge transport on current-voltage characteristics and power-conversion efficiency of organic solar cells
JF  - Nature Communications
N2  - This work elucidates the impact of charge transport on the photovoltaic properties of organic solar cells. Here we show that the analysis of current-voltage curves of organic solar cells under illumination with the Shockley equation results in values for ideality factor, photo-current and parallel resistance, which lack physical meaning. Drift-diffusion simulations for a wide range of charge-carrier mobilities and illumination intensities reveal significant carrier accumulation caused by poor transport properties, which is not included in the Shockley equation. As a consequence, the separation of the quasi Fermi levels in the organic photoactive layer (internal voltage) differs substantially from the external voltage for almost all conditions. We present a new analytical model, which considers carrier transport explicitly. The model shows excellent agreement with full drift-diffusion simulations over a wide range of mobilities and illumination intensities, making it suitable for realistic efficiency predictions for organic solar cells.
Y1  - 2015
U6  - https://doi.org/10.1038/ncomms7951
SN  - 2041-1723
VL  - 6
PB  - Nature Publ. Group
CY  - London
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  -