Abstract

A Bismuth halide-based perovskite is an emerging, potent material due to its lower toxicity, high chemical stability at ambient temperatures, as well as its outstanding photo-absorbing capability in photovoltaic applications, with properties similar to those of lead-halide-based photovoltaics. The organic hole-transport materials, such as Spiro-OMeTAD and PEDOT: PSS, are used to fabricate perovskite solar cells; however, they are expensive and easily degrade. Therefore, in this study, an attempt was made to fabricate free hole transport layer (HTL) perovskite solar cells with MA3Bi2I9 (MBI) by solvent engineering, which can tune the band gap and surface morphology of the thin film to improve efficiency. Herein, we utilize the solvents Dimethylformamide (DMF) and Dimethyl Sulfoxide (DMSO) to investigate their influence on the band gap and properties of the MBI material. Here, the MBI thin films are fabricated by a simple one-step spin coating method. The hexagonal crystal structure is confirmed by XRD analysis for both films. The UV absorbance of the films is examined, with prominent peaks at 520 nm and 450 nm for the DMF solvent. For the DMSO solvent, the peaks are observed at 510 nm, 431 nm, and 360 nm, respectively. The band gap of DMF and DMSO solvents is 2.25 eV and 2.24 eV, respectively. The photoemission spectra obtained for both films are centered at 474 nm. The formation of perovskite is confirmed by FTIR analysis. The solar cell device is fabricated without a hole transport layer and analyzed using solvent engineering to enhance photovoltaic device performance. DMSO solvent-based solar cell device exhibited 32% more efficient cell performance than the DMF solvent-based solar cell device. © The Author(s) 2025.