Why Perovskite Exhibits Photovoltaic Current–Voltage Hysteresis While Sb 2 Se 3 Does Not: Insights from Bias-Dependent Spectroscopic Response

Understanding why hybrid halide perovskites show pronounced photovoltaic current–voltage hysteresis while covalent semiconductors such as Sb 2 Se 3 do not remains a central challenge. We use an in situ three-modality framework, steady-state surface photovoltage (SPV), transient SPV (TSPV), and intensity-modulated photocurrent spectroscopy (IMPS), to compare intrinsic responses of MAPbI 3 and Sb 2 Se 3 thin films under bias. In Sb 2 Se 3 the surface band bending is stable; illumination produces a reversible δ V s linked to rapid electron–hole separation. Its covalent chain network lacks mobile light ions, so interfacial dipoles and space charge are insensitive to bias, and SPV spectra scarcely change, consistent with hysteresis-free I–V curves. In MAPbI 3 mobile ions slowly redistribute under bias, creating quasi-static interfacial dipoles and space charge. Although too slow to follow the modulation frequency, this ionic prepolarization strengthens the surface field, suppresses trap-assisted recombination, and drives a monotonic increase of δ V s with bias. The resulting ion–electron coupled gating deepens depletion and reshapes interface barriers, explaining the pronounced hysteresis and memory in I–V sweeps. TSPV and IMPS fingerprints agree: MAPbI 3 shows long-lived bias-enhanced components and enlarged low-frequency arcs, whereas Sb 2 Se 3 remains dominated by fast separation and recombination without ionic signatures. Bias-dependent SPV thus provides a rapid diagnostic of stability risks in emerging photovoltaics.