Light-dark cycling in perovskite solar cells studied by MPPT and ion migration current measurements

Light-dark cycling is an important test protocol for understanding the degradation and metastability of perovskite solar cells. We first investigated light-dark cycling in a triple-cation mixed-halide lead perovskite solar cell using maximum power point tracking (MPPT) technique and ion migration current measurements and showed that the energy yield during 8 hours of illumination was reduced by light-dark cycles at 45°C. In this case, the concentration of mobile ions, especially slow mobile ions, increased. Next, we investigated light-dark cycling with varying temperatures between 15 to 45 °C. The rate of power decrease under illumination increased with increasing temperature, where slow mobile ions dominated. Moreover, when the power recovered similar values to the initial ones after storage in the dark, slow and fast mobile ion concentrations decreased and increased, respectively, and the total concentrations remained almost unchanged. This indicates the conversion between the fast and slow mobile ions under illumination and dark storage. Our results indicate that the increase in the slow mobile ions, possibly due to deep trap centers, is the primary cause of power reduction for reversible change and irreversible degradation, which can address the long-term reliability of perovskite solar cells.