Solution ALD of (CH₃NH₃)(PbI₃) Perovskite Thin Films Yields Functional Quality and Stability Superior to Classical...

Atomic-level control of solution-processed hybrid halide perovskites is achieved experimentally by solution atomic layer deposition (sALD). This method transfers the surface chemical principles of gas-phase ALD (gALD) to precursors dissolved in the liquid phase. Circumventing limitations associated with precursor volatility, sALD broadens the portfolio of reaction chemistries usable and material classes accessible. We establish its applicability to depositing ultrathin films of ionic semiconductors by developing an sALD procedure for the most prominent halide perovskite, methylammonium triiodoplumbate (CH₃NH₃PbI₃, 'MAPI'). The process saturates upon precursor dosage variation to self-limiting growth typical for ALD, as analyzed by ex-situ and in-situ techniques. sALD-deposited MAPI is highly pure, stoichiometric, and polycrystalline. When MAPI films are prepared in congruent pairs by sALD and by a state-of-the-art spin-coating method, sALD-grown films clearly outperform their spin-coated counterparts in terms of charge carrier lifetimes and stability. They exhibit high carrier mobility and yield functional light absorbing layers in solar cells.