@article{KniepertPaulkePerdigonToroetal.2019,
  author    = {Kniepert, Juliane and Paulke, Andreas and Perdigon-Toro, Lorena and Kurpiers, Jona and Zhang, Huotian and Gao, Feng and Yuan, Jun and Zou, Yingping and Le Corre, Vincent M. and Koster, Lambert Jan Anton and Neher, Dieter},
  title     = {Reliability of charge carrier recombination data determined with charge extraction methods},
  series = {Journal of applied physics},
  volume    = {126},
  journal   = {Journal of applied physics},
  number    = {20},
  publisher = {American Institute of Physics},
  address   = {Melville},
  issn      = {0021-8979},
  doi       = {10.1063/1.5129037},
  pages     = {15},
  year      = {2019},
  abstract  = {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.},
  language  = {en}
}
@article{StolterfohtLeCorreFeuersteinetal.2019,
  author    = {Stolterfoht, Martin and Le Corre, Vincent M. and Feuerstein, Markus and Caprioglio, Pietro and Koster, Lambert Jan Anton and Neher, Dieter},
  title     = {Voltage-Dependent Photoluminescence and How It Correlates with the Fill Factor and Open-Circuit Voltage in Perovskite Solar Cells},
  series = {Acs energy letters},
  volume    = {4},
  journal   = {Acs energy letters},
  number    = {12},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {2380-8195},
  doi       = {10.1021/acsenergylett.9b02262},
  pages     = {2887 -- 2892},
  year      = {2019},
  abstract  = {Optimizing the photoluminescence (PL) yield of a solar cell has long been recognized as a key principle to maximize the power conversion efficiency. While PL measurements are routinely applied to perovskite films and solar cells under open circuit conditions (V-OC), it remains unclear how the emission depends on the applied voltage. Here, we performed PL(V) measurements on perovskite cells with different hole transport layer thicknesses and doping concentrations, resulting in remarkably different fill factors (FFs). The results reveal that PL(V) mirrors the current-voltage (JV) characteristics in the power-generating regime, which highlights an interesting correlation between radiative and nonradiative recombination losses. In particular, high FF devices show a rapid quenching of PL(V) from open-circuit to the maximum power point. We conclude that, while the PL has to be maximized at V-OC at lower biases < V-OC the PL must be rapidly quenched as charges need to be extracted prior to recombination.},
  language  = {en}
}