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
T2  - 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
UR  - https://publishup.uni-potsdam.de/frontdoor/index/index/docId/47790
SN  - 0021-8979
SN  - 1089-7550
VL  - 126
IS  - 20
PB  - American Institute of Physics
CY  - Melville
ER  -