Sequential Formation of Tunable-Bandgap Mixed-Halide Lead-Based Perovskites: In Situ Investigation and Photovoltaic Devices

Inorganic-organic hybrid perovskites MAPb(IxBr1-x)(3) (0 < x < 1) hold promise for efficient multi-junction or tandem solar cells due to tunable bandgap and improved long-term stability. However, the phase transformation from Pb(IxBr1-x)(2) precursors to perovskites is not fully understood which hinders further improvement of optoelectronic properties and device performance. Here, adaptation of the two-step deposition method, which enables the direct probe into the growth dynamics of perovskites using in situ diagnostics, and a detailed view of the effects of solvent, lead halide film solvation, and Br incorporation and alloying on the transformation behavior is presented. The in situ measurements indicate a strong tendency of lead halide solvation prior to crystallization during solution-casting Pb(IxBr1-x)(2) precursor from a dimethyl sulfoxide (DMSO) solvent. Highly-efficient intramolecular exchange is observed between DMSO molecules and organic cations, leading to room-temperature conversion of perovskite and high-quality films with tunable bandgap and superior optoelectronic properties in contrast to that obtained from crystalline Pb(IxBr1-x)(2). The improved properties translate to easily tunable and a relatively higher power conversion efficiency of 16.42% based on the mixed-halide perovskite MAPb(I0.9Br0.1)(3). These findings highlight the benefits that solvation of the precursor phases, together with bromide incorporation, can have on the microstructure, morphology, and optoelectronic properties of these films.

Automated summary

The study suggests that solvation of the lead halide precursor phases, together with bromide incorporation, can significantly improve the microstructure, morphology, and optoelectronic properties of the inorganic-organic hybrid perovskite films.