Saturation of Open-Circuit Voltage at Higher Light Intensity Caused by Interfacial Defects and Nonradiative Recombination Losses in Perovskite Solar Cells

A new analytical expression that directly relates the open-circuit voltage (V_oc) in perovskite solar cells (PSCs) to the quasi-Fermi level splitting (QFLS), interface energy offsets, and nonradiative recombination losses has been derived. It is found that the QFLS of the active layer plays a dominant role in enhancing V_oc of PSCs. The newly derived V_oc is applied to two PSCs with the hole transport layer (HTL) of poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine], and poly(3-hexylthiophene-2,5-diyl) (P3HT) and found that the first PSC has a higher V_oc, which agrees well with the experimental results. It is found that both PSCs exhibit saturation of V_oc at the higher charge carrier generation rates and hence at higher light intensities. The lower V_oc in PSC with P3HT as HTL is attributed to the stronger band bending and higher interfacial defects. In accordance with the results, a large quasi-Fermi level splitting and a minimal interfacial energy offsets may be considered when selecting material for high V_oc PSCs.