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The light soaking phenomenon, in chlorine-based mixed halide perovskite solar cells (PSC) with p-i-n configuration, is studied. Due to light soaking, the solar cells have shown improved open circuit voltage, fill factor (FF), and power conversion efficiency without much change in short circuit current. The devices have returned to their original state upon extended exposure to dark conditions. Capacitance spectroscopy is used to understand the effect of light soaking on various photovoltaic parameters. The observed increase of capacitance value with light soaking in the low frequency region of the capacitance-frequency (C-F) plot is elucidated, as the coupled effect of electronic and ionic processes involving defects. The decrement in the mid-frequency capacitance is attributed to an increase in the width of the depletion region which eventually facilitated the improvement in open circuit voltage and FF. Defect densities, and its distribution in the energy space, are deduced before and after light soaking. The defects density of states of PSC studied are found to reduce from 10 16 to 10 15 eV −1 cm −3 , with a Gaussian distribution, and having a peak energy shift from 0.27 to 0.26 eV.

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Uniform and high-electronic-quality perovskite thin films are necessary for high efficiency perovskite solar cells (PSCs) and additives play a major role in improving the quality of the perovskite films. Here, we demonstrate acetylammonium chloride (AAC) as an additive to effectively control the morphology and crystal quality of the methylammonium lead iodide perovskite film. AAC incorporated PSCs have shown an improved power conversion efficiency (PCE) of 15.9% compared to 14.9% of the control device. Furthermore, AAC incorporated PSCs exhibit high operational stability by retaining 89% of the initial efficiency after 150 hours of continuous operation while the control devices degrade to 51% of the initial PCE in just 45 hours. The improved performance and stability of the AAC incorporated PSCs can be attributed to the (1) formation of uniform sized perovskite films of larger grains and (2) passivation of defects present in the grain boundaries and surfaces of the perovskite film. The defect density has reduced from 4.1x1016 cm-3 to 1.97x1016 cm-3 on addition of AAC to the perovskite film. The reduction in defects-induced non-radiative recombination decay pathways, as further verified from impedance and capacitance-frequency measurements, has caused an enhancement in the open circuit voltage of the AAC incorporated devices and thus an improvement in the PCE and stability of the devices.