Triple cation additive NH3+C2H4NH2+C2H4NH3+-induced phase-stable inorganic -CsPbI3 perovskite films for use in solar cells

We demonstrate that employing a small quantity of triple cation NH3+C2H4NH2+C2H4NH3+ (denoted as DETA(3+)) could effectively stabilize mutable -CsPbI3 for 60 d via a facile one-step deposition method without any encapsulation. Reasons for the remarkable improvement of phase-stability for CsPbI3 are generalized into three aspects: (1) the reduction of CsPbI3 crystalline grains, (2) avoiding spontaneous octahedral tilting caused by ionic bonds between NH3+ or RNH2+ groups of DETA(3+) and I- of [PbI6](4-) in CsPbI3 perovskite crystals formed on the surface or grain boundaries of the CsPbI3 and (3) enhancement of the hydrophobicity of inorganic perovskite layers induced by the oil-wet (hydrophobic) hydrocarbon chains of DETA(3+) aggregated on the surfaces. Excellent photovoltaic properties of the CsPbI(3)xDETAI(3) perovskite films with reduced nonradiative recombination are achieved. The best solar cell with the configuration of FTO/compact-TiO2/CsPbI(3)xDETAI(3)/P3HT/Au shows a power conversion efficiency (PCE) of 7.89% and retains 92% of its initial PCE after storage for 1008 h in a dark dry box without any encapsulation.