TY  - JOUR
A1  - Perdigon-Toro, Lorena
A1  - Zhang, Huotian
A1  - Markina, Anastaa si
A1  - Yuan, Jun
A1  - Hosseini, Seyed Mehrdad
A1  - Wolff, Christian Michael
A1  - Zuo, Guangzheng
A1  - Stolterfoht, Martin
A1  - Zou, Yingping
A1  - Gao, Feng
A1  - Andrienko, Denis
A1  - Shoaee, Safa
A1  - Neher, Dieter
T1  - Barrierless free charge generation in the high-performance PM6:Y6 bulk heterojunction non-fullerene solar cell
JF  - Advanced materials
N2  - Organic solar cells are currently experiencing a second golden age thanks to the development of novel non-fullerene acceptors (NFAs). Surprisingly, some of these blends exhibit high efficiencies despite a low energy offset at the heterojunction. Herein, free charge generation in the high-performance blend of the donor polymer PM6 with the NFA Y6 is thoroughly investigated as a function of internal field, temperature and excitation energy. Results show that photocurrent generation is essentially barrierless with near-unity efficiency, regardless of excitation energy. Efficient charge separation is maintained over a wide temperature range, down to 100 K, despite the small driving force for charge generation. Studies on a blend with a low concentration of the NFA, measurements of the energetic disorder, and theoretical modeling suggest that CT state dissociation is assisted by the electrostatic interfacial field which for Y6 is large enough to compensate the Coulomb dissociation barrier.
KW  - driving force
KW  - non-fullerene acceptors
KW  - organic solar cells
KW  - photocurrent generation
Y1  - 2020
U6  - https://doi.org/10.1002/adma.201906763
SN  - 0935-9648
SN  - 1521-4095
VL  - 32
IS  - 9
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Kniepert, Juliane
A1  - Paulke, Andreas
A1  - Perdigon-Toro, Lorena
A1  - Kurpiers, Jona
A1  - Zhang, Huotian
A1  - Gao, Feng
A1  - Yuan, Jun
A1  - Zou, Yingping
A1  - Le Corre, Vincent M.
A1  - Koster, Lambert Jan Anton
A1  - Neher, Dieter
T1  - Reliability of charge carrier recombination data determined with charge extraction methods
JF  - Journal of applied physics
N2  - Charge extraction methods are popular for measuring the charge carrier density in thin film organic solar cells and to draw conclusions about the order and coefficient of nongeminate charge recombination. However, results from such studies may be falsified by inhomogeneous steady state carrier profiles or surface recombination. Here, we present a detailed drift-diffusion study of two charge extraction methods, bias-assisted charge extraction (BACE) and time-delayed collection field (TDCF). Simulations are performed over a wide range of the relevant parameters. Our simulations reveal that both charge extraction methods provide reliable information about the recombination order and coefficient if the measurements are performed under appropriate conditions. However, results from BACE measurements may be easily affected by surface recombination, in particular for small active layer thicknesses and low illumination densities. TDCF, on the other hand, is more robust against surface recombination due to its transient nature but also because it allows for a homogeneous high carrier density to be inserted into the active layer. Therefore, TDCF is capable to provide meaningful information on the order and coefficient of recombination even if the model conditions are not exactly fulfilled. We demonstrate this for an only 100 nm thick layer of a highly efficient nonfullerene acceptor (NFA) blend, comprising the donor polymer PM6 and the NFA Y6. TDCF measurements were performed as a function of delay time for different laser fluences and bias conditions. The full set of data could be consistently fitted by a strict second order recombination process, with a bias- and fluence-independent bimolecular recombination coefficient k(2) = 1.7 x 10(-17)m(3) s(-1). BACE measurements performed on the very same layer yielded the identical result, despite the very different excitation conditions. This proves that recombination in this blend is mostly through processes in the bulk and that surface recombination is of minor importance despite the small active layer thickness. Published under license by AIP Publishing.
Y1  - 2019
U6  - https://doi.org/10.1063/1.5129037
SN  - 0021-8979
SN  - 1089-7550
VL  - 126
IS  - 20
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Gao, Feng
A1  - Wang, Jianpu
A1  - Blakesley, James C.
A1  - Hwang, Inchan
A1  - Li, Zhe
A1  - Greenham, Neil C.
T1  - Quantifying loss mechanisms in polymer Fullerene photovoltaic devices
JF  - dvanced energy materials
KW  - organic photovoltaics
KW  - recombination
KW  - bulk heterojunctions
KW  - loss mechanisms
KW  - drift-diffusion models
Y1  - 2012
U6  - https://doi.org/10.1002/aenm.201200073
SN  - 1614-6832
VL  - 2
IS  - 8
SP  - 956
EP  - 961
PB  - Wiley-VCH
CY  - Weinheim
ER  -