Thiourea Small Molecules Regulated Slow Passivation in MAPbI₃ Thin Films for Enhanced Stability and Performance of Perovskite Solar Cells

The low stability of perovskite solar cells is the limiting factor for their commercialization, which is largely affected by defects originating from crystallographic distortions and interface formation in solution-processed lead halide perovskite thin films. Herein, urea and thiourea small molecules are used as dopants to synergistically increase the power conversion efficiency (PCE) and stability of the perovskite solar cells by regulating the morphology and crystallinity of the perovskite thin films. X-ray diffraction, atomic force microscopy, Fourier-transform infrared spectroscopy, transmittance spectra, day-dependent photoluminescence (PL), and Raman scattering spectra are used to briefly compare the crystal growth and defect passivation mechanisms of urea and thiourea small molecules. The PCE of thiourea-doped perovskite solar cells gradually increases as a function of storage duration, from 12.12 ± 0.15% to 18.38 ± 89% in 40 days. Day-dependent PL and Raman scattering spectra reveal that the crystallinity of the thiourea-doped perovskite thin film improves over time, resulting in slow passivation from thiourea small molecules and consequently an improvement in device performance.