Comprehensive crystallization retardation of inorganic perovskites for high performance inverted solar cells†

Inverted inorganic perovskite solar cells (PSCs) are ideal top cells for tandem configurations due to their ideal bandgap and excellent thermal stability. However, water-induced rapid crystallization during inorganic perovskite film processing in ambient air is difficult to control. Here, we report a crystallization retardation method to prepare inorganic perovskite films by incorporating an acrylonitrile-methyl acrylate copolymer (AMAC) in perovskite precursor solution. Firstly, the strong interaction between the AMAC and the precursor solution yields increased colloidal size, delays dimethyl sulfoxide (DMSO) volatilization during annealing and postpones the phase transition. Secondly, the interaction between AMAC and dimethylamine (DMA⁺) slows down ion exchange with Cs⁺. These interactions retard perovskite crystallization, increase pack-crystal grain size and reduce residual stress. Combined with the functional groups in AMAC, the incorporation of the AMAC reduces defects in perovskite films, modulates interfacial energy levels, and prolongs charge lifetimes, inhibiting the migration of iodide ions. Ultimately, the power conversion efficiency (PCE) of the AMAC-incorporated inverted (p–i–n) and conventional (n–i–p) PSCs reaches 21.7% and 21.8%, respectively, while the unencapsulated devices show only 8% degradation over 2500 h of maximum power point tracking and continuous operation.