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

Abstract

We demonstrate that employing a small quantity of triple cation NH₃⁺C₂H₄NH₂⁺C₂H₄NH₃⁺ (denoted as DETA³⁺) could effectively stabilize mutable α-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 DETA³⁺ 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 DETA³⁺ aggregated on the surfaces. Excellent photovoltaic properties of the CsPbI₃·xDETAI₃ perovskite films with reduced nonradiative recombination are achieved. The best solar cell with the configuration of FTO/compact-TiO₂/CsPbI₃·xDETAI₃/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.