Effects of negative hydroxyl ions at the SnO₂/perovskite layer interface on the performance of perovskite solar cells

In this work we studied the effects of negative hydroxyl ions at the SnO₂/perovskite layer interface with respect to the performance of perovskite solar cells (PSCs). We considered a layer of 1 nm thickness, containing fixed negative ions, at the SnO₂/perovskite layer interface. The density of the ions was set to 7 × 10¹⁹ cm⁻³ in our simulations. To maintain charge neutrality in the SnO2 electron transport layer (ETL), we calculated the number of negative ions in the 1-nm-thick layer and added the same number of positive ions to the remaining part of the ETL. According to our simulation results, the negative ions increased the internal potential drop, reducing the open-circuit voltage of the perovskite solar cell from 0.99 to 0.88 V. On the other hand, the negative non-mobile hydroxyl ions at the interface absorbed some of the mobile positive ions of the perovskite layer, which increased the hysteresis index from 0.177% to 0.707%.