Insights into the Open Circuit Voltage of Perovskite Solar Cells under Low Indoor Lighting

The rapidly growing interest in indoor photovoltaics for low light energy harvesting applications further necessitates an understanding of factors that impact the performance and efficiency of these devices under low light. The external radiative efficiency of a photovoltaic device is an important parameter to help understand the impact of nonradiative recombination on the open circuit voltage (Voc) of the device. In this work, we compare the behavior of Voc with the photocurrent under low light for two perovskite PV devices, one of which is fabricated with an additional surface passivation treatment. In order to explain the observed Voc differences between the two cells, we performed absolute electroluminescence measurements on both cells and explored the current density dependence of the external radiative efficiency between the two cells. This dependence is quantified with a mathematical treatment that takes advantage of a widely accepted recombination current model. Our findings indicate that surface-passivated cells substantially benefit from a modest decrease in the reverse saturation current density associated with nonradiative losses, resulting in large Voc enhancements and increased luminescence extraction efficiency, particularly under low light conditions.