Solid Electrolyte Interphase Formation in Tellurium Iodide Perovskites during Electrochemistry and Photoelectrochemistry.

Halide perovskites are promising photoelectrocatalytic materials. Their further development requires understanding of surface processes during electrochemistry. Thin films of tellurium-based vacancy-ordered perovskites with formula A ₂ TeI ₆ , A = Cs, methylammonium (MA), were deposited onto transparent conducting substrates using aerosol-assisted chemical vapor deposition. Thin film stability as electrodes and photoelectrodes was tested in dichloromethane containing tetrabutylammonium PF ₆ (TBAPF ₆ ). Using photoemission spectroscopy, we show that the formation of a solid electrolyte interphase on the surface of the Cs ₂ TeI ₆ , consisting of CsPF ₆ , enhances the stability of the electrode and allows extended chopped-light chronoamperometry measurements at up to 1.1 V with a photocurrent density of 16 μA/cm ² . In contrast, (CH ₃ NH ₃ ) ₂ TeI ₆ does not form a passivating layer and rapidly degrades upon identical electrochemical treatment. This demonstrates the importance of surface chemistry in halide perovskite electrochemistry and photoelectrocatalysis.