Camphorsulfonic-Salified Chitosan Allowing MACl-Free Stabilization of Pure FAPbI₃ α-Phase via Gravure Printing in Ambient Air

Metal–halide perovskites have gained extreme interest in the photovoltaic field with formamidinium lead iodide (FAPbI₃) currently being one of the best-performing materials for single-junction solar cells. Despite the outstanding record efficiencies, there are still several major issues hindering the large-scale fabrication of perovskite solar cells. The vulnerability to environmental agents along with the need of controlled atmosphere and crystallization aids for the perovskite film deposition represents the major roadblocks. This is particularly true for FAPbI₃ for which the thermodynamically stable phase at room temperature is photovoltaically inactive δ-phase. To address those challenges, herein, a camphorsulfonic-salified chitosan is specifically designed with the aid of DTF calculations to strongly interact with the perovskite and, as a result, improve the morphology and optoelectronic quality of the FAPbI₃. Thanks to the numerous interactions and then the modulation of the solution viscosity, FAPbI₃ devices are fabricated by gravure printing deposition without either antisolvent bath or inclusion of methylammonium chloride (MACl) as additive. The gravure-printed devices with the chitosan feature an enhanced efficiency and stability in air, retaining 80% of the original efficiency after 1200 h in ambient air without any encapsulation.