Sulfonium-based passivation suppresses trap recombination and hysteresis under bright-to-ultra-dim light in perovskite indoor photovoltaics

Lead-halide perovskites (LHPs) are attractive indoor harvesters for self-powered Internet-of-Things (IoT) nodes, yet their output deteriorates under dim lighting (<200 lux) due to intensified trap-assisted recombination and field-driven ion migration, resulting in pronounced current–voltage hysteresis. Here, we show that a single sulfonium capping layer of dimethyl(phenethyl)sulfonium iodide (DMPESI) simultaneously mitigates both loss pathways, enabling stable operation from bright (1000 lux) to ultra-dim (50 lux) white light-emitting diode illumination. DMPESI-passivated indoor photovoltaic cells exhibit a stabilized power-conversion efficiency (PCE) of 31.8% and an open-circuit voltage (VOC) approaching 1 V at 1000 lux, sustain 27.5% PCE at 200 lux, and still deliver 21.9% PCE with VOC ≈ 0.85 V at 50 lux. Across this range, the hysteresis index declines by ≈25%–40%. Transient photovoltage reveals ∼60% longer carrier lifetimes; impedance spectroscopy shows a ≈40% increase in recombination resistance, and capacitance–frequency spectra display a two- to threefold reduction in capacitance at 10 Hz, collectively confirming the simultaneous suppression of trap-assisted recombination and ion migration. An ultrathin sulfonium interlayer (DMPESI) enables stable, low-hysteresis indoor operation across 1000/200/50 lux (IEC TS 62607-7-2:2023). A combined SCLC–IS–KPFM analysis shows a reduction in trap density, suppressed low-frequency ionic response, and a higher perovskite surface work function consistent with enhanced hole extraction. A stabilized 31.8% PCE at 1000 lux is achieved for the 1.6 eV triple-cation CsMAFA-Pb. This approach paves the way for self-powered IoT devices with significantly reduced battery replacement needs, helping to ease the environmental burden of electronic waste.