A stabilized γ-CsPbI3 by poly(allylamine hydrochloride) for wide-band gap perovskites solar cells with enhanced performance

All inorganic perovskite CsPbI3 has been considered as a promising candidate for wide-bandgap solar cells due to its prominent thermal stability and suitable bandgap. However, the cesium cation in the crystal lattice of CsPbI3 seems to be too small to form a stable perovskite crystal structure, resulting in the phase instability of CsPbI3. In this study, we developed a new strategy by adding a small amount of poly(allylamine hydrochloride) (PAACl) additives into the CsPbI3 precursor solution to prepare the stabilized and distorted black phase-based CsPbI3 (gamma-CsPbI3) thin films. The passivation effect through chemical bonding between PAACl and CsPbI3 was investigated systematically by Fourier transformed infrared (FTIR) and X-ray photoelectric spectroscopy (XPS) techniques. The PAACl existed in the perovskite thin films enhance the crystal quality of gamma-CsPbI3 with high crystallinity and long carrier life time, and further achieved a power conversion efficiency of 17.8%. Moreover, the present CsPbI3-based perovskite solar cells showed improved stability, maintained 90% of its initial efficiency after exceeding 30 days under 30% humidity environment without encapsulation.