Perovskite Solar Cells on the Way to Their Radiative Efficiency Limit - Insights Into a Success Story of High Open-Circuit Voltage and Low Recombination

Inorganic-organic lead-halide perovskite solar cells have reached efficiencies above 22% within a few years of research. Achieved photovoltages of >1.2 V are outstanding for a material with a bandgap of 1.6 eV - in particular considering that it is solution processed. Such values demand for low non-radiative recombination rates and come along with high luminescence yields when the solar cell is operated as a light emitting diode. This progress report summarizes the developments on material composition and device architecture, which allowed for such high photovoltages. It critically assesses the term "lifetime", the theories and experiments behind it, and the different recombination mechanisms present. It attempts to condense reported explanations for the extraordinary optoelectronic properties of the material. Amongst those are an outstanding defect tolerance due to antibonding valence states and the capability of bandgap tuning, which might make the dream of low-cost highly efficient solution-processed thin film solar cells come true. Beyond that, the presence of photon recycling will open new opportunities for photonic device design.