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 TiO ₂ at a high temperature before adding the SnO ₂ 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 TiO ₂@SnO ₂ nanocrystals for bilayered ETL. The introduction of SnO ₂ enhances the Fermi level and lowers the valence band position of TiO ₂ nanocrystals, which facilitates electron extraction and hole blocking, leading to the enhancement of open circuit voltage and fill factor. Additionally, TiO ₂@SnO ₂ nanocrystals provide a more suitable refractive index and less parasitic absorption than TiO ₂, 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 TiO ₂@SnO ₂ ETL.