Influence of environment and light-stress on the opto-electronic properties of triple-cations perovskite thin films.

In this work we study the transport properties of triple-cation halide perovskite thin films and their evolution when exposed to air or vacuum, and after light-soaking. Transport parameters were investigated by steady state dark and photocurrent methods as well as by the steady state photocarrier grating experiment (SSPG) from which the ambipolar diffusion length of thin film materials is estimated. Combined with other characterization measurements, such as photoluminescence and Fourier transform photocurrent spectroscopy, these techniques demonstrate that air plays an important role in the passivation of the surface trap states of the perovskite films. The competition between passivation and degradation of the films under light-soaking was also deeply investigated. Moreover, we show that the degradation of the transport parameters upon light-soaking could be linked mainly to a degradation of the carrier mobility instead of their lifetime.