Metastable changes due to reverse-bias (V_R) treatments in the dark (2–4 samples per condition). (a) IV characteristics before (dark blue) and after continuous (solid lines) and intermittent (dashed lines) V_R treatments of different durations (colour-coded). (b) Shift of the voltage at 90 mA/cm² (see grey line in a), (c) shift in capacitance at 0 V, and (d) shift in doping density (ratio: ) after reverse-bias treatments of different durations (“on”-time) and different modes (continuous: circles, intermittent: squares).