Abstract

We have developed an environmentally friendly mixed-halide perovskite MA₃Bi₂Cl_9 – xI_x with a band-gap funnel structure. However, the dynamic interfacial interactions of band-gap funneling in MA₃Bi₂Cl_9 – xI_x perovskites in the photoelectrochemical (PEC) system remain ambiguous. In light of this, we prepared single- and mixed-halide lead-free bismuth-based hybrid perovskites — MA₃Bi₂Cl_9 – yI_y and MA₃Bi₂I₉ (named MBCl‑I and MBI) — in the presence and absence of the band-gap funnel structure, respectively.

Using temperature-dependent transient photoluminescence and electrochemical voltammetric techniques, we therefore confirmed the photophysical and (photo)electrochemical phenomena of solid – solid and solid – liquid interfaces for MBCl‑I and MBI halide perovskites. Concerning the mixed-halide hybrid perovskites MBCl‑I with a band-gap funnel structure, stronger electronic coupling arising from an enhanced overlap of electronic wavefunctions results in more efficient exciton transport.

Besides, MBCl-I’s effective diffusion coefficient and electron transfer rate demonstrate efficient heterogeneous charge transfer at the solid – liquid interface, generating improved photoelectrochemical hydrogen production. Consequently, this combination of photophysical and electrochemical techniques opens up an avenue to explore the intrinsic and interfacial properties of semiconductor materials for elucidating the correlation between material characterisation and device performance.