Phase-pure Ruddlesden–Popper tin halide perovskites for solar energy conversion applications

Abstract

Two-dimensional Ruddlesden–Popper (RP) tin halide perovskites have recently shown promise in solar energy conversion applications owing to their low-toxicity and low-cost processability. However, RP tin halide perovskites typically consist of multiple phases with enormously disordered crystal orientation, lowering their power conversion efficiency. Herein, we show a new method to prepare phase-pure RP tin hybrid perovskite films by fluorinating the conventionally used spacer cation C₆H₅CH₂NH₃⁺ (abbreviated as FBE⁺). This solvophobic engineering strategy decreases the interaction among spacer cations and solvent molecules to induce the self-assembly of FBE⁺ cations into micelles. These micelles in the solvent capture tin iodide components, forming crystal nuclei. This “simultaneous” crystallization mode leads to uniformly distributed nuclei and further results in a phase-pure RP perovskite with vertical crystal orientation. The resultant phase pure FBE₂FA₃Sn₄I₁₃ perovskite exhibits an improved carrier mobility and much reduced trap density, which are favourable for solar energy conversion applications. A power conversion efficiency of 9.25% was achieved for the FBE₂FA₃Sn₄I₁₃ perovskite solar cell, which is among the highest efficiencies reported for state-of-the-art two-dimensional RP tin hybrid perovskite cells.