Stabilizing 2D Pt‐Based Halide Perovskites via Solvent Lone Pair Donation

Abstract Platinum‐based halide perovskites exhibit promising optoelectronic properties along with merits of low‐temperature processing and stability. Current research on Pt halide perovskites is limited to 0D A ₂ BX ₆ structure as the ABX ₃ 3D structure is thermodynamically unstable. Herein, the study reports the stabilization of the ABX ₃ structure into a 2D layered phase, CsPtI ₃ (DMSO), that is stable up to 181.5 °C. The 2D phase shows an excitonic peak at the absorption edge of 600 nm, indicating quantum confinement. It also exhibits a large Stokes shift due to intersystem crossing (ISC), with a quenched singlet excitonic fluorescence at 610 nm and strong triplet emission at 852 nm. Pt(II) co‐ordinates with dimethyl sulfoxide (DMSO) via σ‐donation of S lone‐pair electrons and π‐ back donation from Pt to S, stabilizing CsPtI ₃ (DMSO) layered structure. The strong electronic interaction between DMSO and Pt(II) and orbital mixing lead to spin‐orbit‐coupling, facilitating ISC and singlet‐to‐triplet exciton energy transfer. The interaction of Pt and DMSO is further confirmed by addition of thioacetamide (TAA), a strong S‐donor, which retards the formation of 2D layered structure, and directly results in Cs ₂ PtI ₆ and Pt.