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

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_0.17FA_0.83)_0.95Pb(I_0.83Br_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.