Effects of PbI2 addition and TiO2 electron transport layers for perovskite solar cells

TiO2/CH3NH3PbI3−xClx-based photovoltaic cells added with PbI2 were fabricated and investigated. The fill factor and open-circuit voltage of the cell with 16 nm TiO2 nanoparticles were increased by PbI2 addition. For the cell, the short-circuit current density and open-circuit voltage were increased by using 23 nm TiO2 nanoparticles in place of 16 nm TiO2 nanoparticles. The external quantum efficiency increased, which would be due to the improved interface between the TiO2 and perovskite layers. As a result, the conversion efficiency was improved by adding PbI2 and using 23 nm TiO2 nanoparticles. X-ray diffraction showed that the perovskite crystals changed from cubic to tetragonal, which resulted in the improved stability of the perovskite solar cell by PbI2 addition.