Two-dimensional (2-D) metal halide perovskites (LA)m(A)n-1(B)n(X)3n+1 are hybrid organic-inorganic materials that have great potential as next-generation solar cells, LEDs, and photodetectors, however their common usage of lead (B=Pb) limits their application and commercialization due to their environmental and physiological toxicity. Tin-based perovskites (B=Sn) can serve as a clear, nontoxic analogue, but tin perovskite phases generally possess lower defect tolerance and greater instability to oxidation compared to their lead counterparts. This research seeks to circumvent these limitations of tin halide perovskite phases through the engineering of the 2-D solid state structure. Conventionally, the organic long-chain ammonium (LA) spacer cations that bisect n layers of BX6 octahedra introduce nonpolar character to the crystal structure and enable greater air and moisture stability compared to ionic 3-D perovskite phases. This work utilizes bulkier and more rigid LA cations with stronger nonpolar aromatic interactions that can better isolate the tin halide SnX6 octahedra from air and can limit or entirely prevent structural degradation due to air exposure, as evaluated through PXRD patterns and PL measurements over time.

Enhancing the stability of two-dimensional tin halide perovskites through spacer cation engineering

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