We report a systematic investigation on the role of excess PbI ₂ content in CH ₃ NH ₃ PbI ₃ perovskite film properties, solar cell parameters and device storage stability.

Charge carriers’ density, their lifetime, mobility, and the existence of trap states are strongly affected by the microscopic morphologies of perovskite films, and have a direct influence on the photovoltaic performance. Here, we report on micro-wrinkled perovskite layers to enhance photocarrier transport performances. By utilizing temperature-dependent miscibility of dimethyl sulfoxide with diethyl ether, the geometry of the microscopic wrinkles of the perovskite films are controlled. Wrinkling is pronounced as temperature of diethyl ether (T_DE) decreases due to the compressive stress relaxation of the thin rigid film-capped viscoelastic layer. Time-correlated single-photon counting reveals longer carrier lifetime at the hill sites than at the valley sites. The wrinkled morphology formed at T_DE = 5 °C shows higher power conversion efficiency (PCE) and better stability than the flat one formed at T_DE = 30 °C. Interfacial and additive engineering improve further PCE to 23.02%. This study provides important insight into correlation between lattice strain and carrier properties in perovskite photovoltaics.

We demonstrate that the often observed double peak emission in lead halide perovskites is caused by an extensive self-absorption effect.