Role of light trapping in the reciprocity between absorptance and photoluminescence in hybrid halide perovskite layers

Hybrid perovskites are highly attractive for a range of optoelectronic applications. In the case of solar cells, a film thickness close to 1 micrometre is necessary to absorb most of the light. Otherwise, either a back reflector or an efficient light trapping strategy may be desired. Light trapping due to the light scattering on rough surfaces is the most straightforward method to increase optical path of light inside the absorber. Using this approach, we prepared experimentally layers featuring an absorptance enhancement that was corresponding to the photon path length extension several times. In parallel, we measured photoluminescence and recalculated it into absorptance employing reciprocity theorem. We could verify the validity of the theorem even for layers featuring light trapping, however, we identified many cases where the simple reciprocity applied on macroscopic measurable properties does not work.