Correlation between Charge Transport Length Scales and Dielectric Relaxation Time Constant in Hybrid Halide Perovskite Semiconductors

The charge carrier diffusion length and dielectric relaxations are important parameters which decide the performance of various optoelectronic devices, in particular for photovoltaic devices. A comparative study is carried out on the charge transport length scale (L) for passivated and pristine CH3NH3PbI3 (MAPI) thin-film-based perovskite solar cells (PSCs) through scanning photocurrent microscopy (SPM). The SPM study suggested an improved L and degree of ambipolarity of photogenerated charge carriers (electron and hole) in passivated as compared to pristine MAPI-based PSCs. These results were found to be correlated with frequency-dependent photocurrent measurement, which shows that the relaxation time of the charge carrier is relatively lower in passivated MAPI-based PSCs. This mechanism could be explained by trap-assisted recombination, where trap states are induced by ion migration in halide perovskite films. Furthermore, passivation of traps showed an increased degree of ambipolarity in the perovskite semiconductor thin film.