Low Density of Conduction and Valence Band States Contribute to the High Open-Circuit Voltage in Perovskite Solar Cells

Hybrid perovskites are widely used for high-performance solar cells. Large diffusion lengths and long charge carrier lifetimes are considered two main factors for their high performance. Here, we argue that not only large diffusion lengths and long carrier lifetimes but also the low densities of the conduction and valence band states (N_c, N_v) contribute to high-performance perovskite solar cells. We estimated N_c and N_v of silicon, CdTe, and typical perovskites with two different methods. It was found that N_c and N_v of perovskites and CdTe are much lower than that of silicon. Using numerical models, we found that the solar cell of a material with same characteristics but lower N_c and N_v can realize a higher open-circuit voltage (V_oc) and higher power conversion efficiency (PCE). We put forward and proved that the low N_c and N_v in hybrid perovskite is one of the factors for its high performance. This provides a new guideline for finding and developing new photovoltaic candidate materials.