Mechanism study on enhanced open-circuit voltage of perovskite solar cells with vapor-induced TiO2 as electron-transport layer

This study presents an effective method to enhance the open-circuit voltage (VOC) of methylammonium lead iodide (MAPbI3) perovskite solar cell. The electron transport layer (ETL) of TiO2 is prepared via a vapor-induced process at 180 °C, much lower than the processing temperature of TiO2 for the conventional device typically beyond 500 °C. Such vapor-induced method has been demonstrated to introduce hydroxyl group (OH) onto the surface of TiO2 without changing the crystal phase of the bulk TiO2, while the surface state for TiO2 film can be modified, which subsequently results in the increasement of its work function and enlarges the energy gap between TiO2 layer and Au anode. As a result, a VOC of 1.03 V for MAPbI3 solar cell based on 180 °C-TiO2 is attained with an increment of 0.2 V from 0.84 V for the devices with 500 °C-TiO2 as ETL. The maximum power conversion efficiency is also raised by about 20% compared to the control device with 500 °C-TiO2 as ETL.