Charge Carrier Collection Losses in Lead-Halide Perovskite Solar Cells

The collection of photogenerated charges in halide perovskite solar cells depends on the thickness of the absorber layer, with larger thicknesses leading to a reduced collection efficiency. This observation has traditionally been associated with insufficiently high electron and hole diffusion lengths in the absorber layers. However, it is shown that in the presence of low-mobility contact layers, charge collection can be thickness-dependent, even if the absorber layer has infinite mobility. Here, analytical equations are derived for the thickness dependence of charge collection losses in situations where recombination is bulk or interface-limited and show how to relate these equations to voltage-dependent photoluminescence data. The analytical equations are compared to experimental data and numerical simulations and it is observed that experimental data on triple-cation perovskite devices with different thicknesses approximately follows the case, where bulk recombination dominates.