Electromodulation and Transient Absorption SpectroscopySuggest Conduction Band Electron Lifetime, Electron Trapping Parameters,and CH 3 NH 3 PbI 3 Solar Cell Fill FactorAre Correlated

While lead halide perovskite solar cells have shown a steady increase in power conversion efficiencies over the last several years, it is well known that minor variations in film fabrication conditions have a major impact on solar performance. In comparing devices assembled with either a 1-step or 2-step CH3NH3PbI3 film fabrication, we observe an increased fill factor and decreased sub-gap photocurrent in devices made with the 1-step method. These sub-gap states correlate with bleaching in NIR transient absorption measurements. We also observe induced absorptions in this region which we attribute to overlapping signals from photoexcited conduction band (E1/2u → F1/2u) and valence band (F3/2g → E1/2g) carrier transitions. This assignment is consistent with electromodulation spectroscopy under cathodic and anodic charge accumulation conditions, where we observed an absorption onset at a higher energy under electron accumulation (850 nm) compared to that of hole accumulation (1050 nm). Global target analysis...