Interfacial Defects Change the Correlation between Photoluminescence, Ideality Factor, and Open‐Circuit Voltage in Perovskite Solar Cells

Abstract The ideality factor ( n id ) and photoluminescence (PL) analyses assess charge recombination characteristics in perovskite solar cells (PeSCs). However, their correlations with open‐circuit voltage ( V oc ) are often found to be complicated depending on the recombination types in the devices. Herein, the correlation of n id , PL characteristics and V oc is elucidated depending on the interfacial crystal quality in triple‐cation mixed‐halide perovskite, Cs 0.05 (MA 0.17 FA 0.83 ) 0.95 Pb(I 0.83 Br 0.17 ) 3 , deposited on different hole transport layers (HTLs). In the devices with low quality interfacial crystals, V oc increases together with n id , which originates from the light intensity‐dependence of majority carrier at the interface. Meanwhile, a negative correlation between V oc and n id is observed for devices with high quality interfacial crystals. The authors discuss the cases that PL enhancement by the improvement of overall crystal quality can fail to correlate with a V oc increase if interfacial crystal quality becomes worse. The study highlights that interfacial crystal quality evaluation can help to understand charge recombination via n id and PL measurements, and more importantly provide information of which defect engineering between at the interface and in the bulk would be more effective for device optimization.