Enhanced carrier transport and optical gains in perovskite solar cells based on low-temperature prepared TiO2@SnO2 nanocrystals

The bilayered electron transport layer (ETL) has made significant contributions to enhancing the photovoltaic performance for perovskite solar cells. However, it is generally required to prepare the TiO2 at a high temperature before adding the SnO2 layer due to the difference in temperature tolerance, resulting in energy consumption and hampering electron transfer. To address this issue, we proposed a simple low-temperature process based on TiO2@SnO2 nanocrystals for bilayered ETL. The introduction of SnO2 enhances the Fermi level and lowers the valence band position of TiO2 nanocrystals, which facilitates electron extraction and charge blocking, leading to the enhancement of open circuit voltage and fill factor. Additionally, TiO2@SnO2 nanocrystals provide a more suitable refractive index and less parasitic absorption than TiO2, these optical gains forming a higher short-circuit current. As a result, the champion efficiency of the perovskite solar cell was significantly raised from 16.17% to 19.04% along with enhancement in the stability and hysteresis phenomena. Moreover, photovoltaic performance can be further increased by combining perovskite component engineering and interfacial passivation because of the high compatibility of TiO2@SnO2 ETL.