Deep Defect States in Wide-Band-Gap ABX₃ Halide Perovskites

Lead bromide-based halide perovskites are of interest for wide-band-gap (>1.75 eV) absorbers for low-cost solar spectrum splitting to boost solar-to-electrical energy conversion efficiency/area by adding them to c-Si or Cu(In,Ga)Se₂ PV cells and for photoelectrochemical solar fuel synthesis. Deep in-gap electronic states in PV absorbers serve as recombination centers and are detrimental for the cell's photovoltaic performance, especially for the open-circuit voltage (V_oc). We find four different deep defect states in polycrystalline layers of mixed-cation lead tribromide from high-sensitivity modulated surface photovoltage (SPV) spectroscopy. Measurements were performed with different contact configurations, on complete solar cells and on samples before and after aging or stressing at 85 °C under illumination. Three of the four states, with energies of ∼0.63, 0.73, and 1.35 eV below the conduction band edge, are assigned to intrinsic defects, whereas defect states in the middle of the band gap could be associated with (uncontrolled) impurities.