Composition-Tuned Wide Bandgap Perovskites: From Grain Engineering to Stability and Performance Improvement

Wide bandgap (WB) organic-inorganic hybrid perovskites (OIHPs) with a bandgap ranging between 1.7 and 2.0 eV have shown great potential to improve the efficiency of single-junction silicon or thin-film solar cells by forming a tandem structure with one of these cells or with a narrow bandgap perovskite cell. However, WB-OIHPs suffer from a large open-circuit voltage (V-oc) deficit in photovoltaic devices, which is associated with the phase segregation of the materials under light illumination. In this work the photoinstability is demonstrated and V-oc loss can be addressed by combining grain crystallization and grain boundary passivation, achieved simultaneously through tuning of perovskite precursor composition. Using FA(0.17)Cs(0.83)PbI(3-x)Br(x) (x = 0.8, 1.2 1.5, and 1.8), with a varied bandgap from 1.72 to 1.93 eV, as the model system it is illustrated how precursor additive Pb(SCN)(2) should be matched with a proper ratio of FAX (I and Br) to realize large grains with defect-healed grain boundaries. The optimized WB-OIHPs show good photostability at both room-temperature and elevated temperature. Moreover, the corresponding solar cells exhibit excellent photovoltaic performances with the champion V-oc/stabilized power output efficiency reaching 1.244 V/18.60%, 1.284 V/16.51%, 1.296 V/15.01%, and 1.312 V/14.35% for WB-OIHPs with x = 0.8, 1.2, 1.5, and 1.8, respectively.