Precursor effects on methylamine gas-induced CH₃NH₃PbI₃ films for stable carbon-based perovskite solar cells

Carbon-based perovskite solar cells (PSCs) without hole transport material have attracted much attention due to their high stability. However, their power conversion efficiency (PCE) is still low because of the lack of suitable perovskite deposition methods. In this work, a facile solid-gas reaction method was explored to prepare high quality perovskite and the effects of precursor composition (PbI₂, PbI₂ + HI, HPbI₃ and PbI₂ + NH₄I) on the CH₃NH₂ (MA) gas-induced perovskite were systematically investigated. The lack of H⁺/I⁻ and/or HI suppressed the conversion of PbI₂ precursor to MAPbI₃, while rapid and complete conversion was achieved for (PbI₂ + HI), HPbI₃ and (PbI₂ + NH₄I) precursors. Compared with HPbI₃ precursor, the presence of H₂O molecules in (PbI₂ + HI) precursor lowered the perovskite crystallinity, while the release of NH₃ from (PbI₂ + NH₄I) precursor slower the interaction of MA molecules with MAPbI₃ for achieving the highest quality MAPbI₃ layer. The application of an anti-solvent treatment during precursor deposition further improved the quality of HPbI₃ and (PbI₂ + NH₄I)-processed perovskite layers, which as a result, significantly promoted the photovoltaic performance of C-PSCs. Both devices exhibited considerably high stability, especially for the (PbI₂ + NH₄I)-processed C-PSCs, who did not show any PCE degradation after storage in air atmosphere at room temperature for 120 days.