Near-infrared photoluminescence from bismuth, a deep defect in cesium lead bromide perovskite

Abstract

Bismuth has been investigated as a potential n-type dopant in hybrid lead halide perovskites, but its behavior in all-inorganic perovskites such as CsPbBr3 has not been thoroughly characterized. We show that Bi behaves as a deep defect in CsPbBr3 and gives rise to broad near-infrared emission, similar to its behavior in hybrid perovskites, but a phenomenon not previously reported in CsPbBr3. Using inverse temperature crystallization, we synthesized a series of Bi-doped CsPbBr3 crystals and quantified their Bi concentrations by inductively coupled plasma optical emission spectroscopy. Bi incorporation redshifted the absorption edge, and hybrid density functional theory calculations show that this increased absorption comes from excitation into the deep donor level of Bi, not from narrowing of the bandgap of CsPbBr3. All Bi-doped crystals emitted both narrow band-edge (2.37 eV) and broad defect-level (1.16 eV) photoluminescence, consistent with our theoretical prediction. Time-resolved photoluminescence measurements indicate that Bi incorporation decreases the lifetime of the band-edge emission and gives rise to long-lived defect emission. Power-dependent photoluminescence measurements conducted at 14 K show that the band-edge peak intensity scales as expected for a free or bound exciton, while the sublinear scaling of the infrared defect peak is consistent with recombination between a free hole and a trapped electron, as proposed by theory. These results demonstrate the quantitative accuracy with which current theoretical approaches predict defect behavior in halide perovskites; such theory is key to guiding the experimental development of doping in these materials.