Effects of annealing temperature on photovoltaic properties of lead-free (CH₃NH₃)₃Bi₂I₉ solar cells

Abstract

Effects of annealing temperature on photovoltaic properties of lead-free (CH₃NH₃)₃Bi₂I₉ solar cells were investigated. The (CH₃NH₃)₃Bi₂I₉ photovoltaic cells were fabricated by a hot air blow-assisted spin-coating method. The spin-coated (CH₃NH₃)₃Bi₂I₉ photoactive layers were annealed at temperatures of 100–150 °C. Current density–voltage characteristics of the (CH₃NH₃)₃Bi₂I₉ photovoltaic cells showed that conversion efficiency increased with increasing annealing temperature. Microstructures and optical properties of the (CH₃NH₃)₃Bi₂I₉ photoactive layers were also investigated by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and ultraviolet–visible–near infrared spectroscopy. The investigation revealed that the changes in lattice constants, crystallite size, surface morphology, and iodide/bismuth ratio of the (CH₃NH₃)₃Bi₂I₉ were attributed to the annealing temperature, resulting in the changes in the photovoltaic properties of the (CH₃NH₃)₃Bi₂I₉ solar cells.