Illumination-Dependent Photocarrier Dynamics in Perovskite Solar Cells Decoded through Electro-Optic Dual-Probe Analysis

Abstract

The performance of solar cells is highly sensitive to variations in light intensity, which naturally fluctuate due to geographic location, weather conditions, and the diurnal solar cycle. Understanding the behavior of photovoltaic devices under such varying illumination is crucial for evaluating their real-world applicability. Although metal halide perovskite solar cells have demonstrated remarkable power conversion efficiencies, their performance under variable light conditions remains underexplored. This study presents a comprehensive investigation into the light-intensity-dependent behavior of perovskite solar cells using a synergistic dual-probe approach that integrates electrical characterization with steady-state and ultrafast optical spectroscopy. Devices fabricated in a p−i−n architecture are evaluated across a wide illumination range (9.5 to 100 mW/cm2), revealing excellent efficiency retention even under low-light conditions. While the short-circuit current density (JSC) shows a sublinear dependence on light intensity (JSC ∝ I0.86), the open-circuit voltage (VOC) displays a weak dependence (VOC ∝ I0.03). Interestingly, the fill factor increases at lower light intensities. Impedance spectroscopy reveals increased resistance and decreased capacitance at reduced intensities, indicating lower carrier densities and suppressed interfacial charge accumulation. Intensity dependent photoluminescence and ideality factor analysis (∼1.15) suggest dominant radiative recombination with minimal nonradiative losses. Power-dependent transient absorption spectroscopy further supports enhanced recombination losses at high excitation powers, which accounts for the sublinear photocurrent behavior. This work provides a comprehensive framework for understanding the photophysical behavior of perovskite solar cells under weak and diffuse illumination conditions encountered in realistic operating environments, including cloudy weather, dawn/dusk illumination, and low-intensity scattered sunlight. These findings offer important insights into the fundamental light-harvesting and charge-transport mechanisms governing perovskite solar cells under low-flux illumination, thereby contributing to the development of efficient photovoltaic systems optimized for weak-light and diffuse-light applications.