Enhanced performance of planar perovskite solar cells using low-temperature processed Ga-doped TiO2 compact film as efficient electron-transport layer

Planar perovskite solar cells (PSCs) based on low-temperature processed gallium (Ga)-doped TiO2 (Ga-TiO2) films and CH3NH3PbI3-xClx active layer have been fabricated by one-step method. The annealing temperature of Ga-TiO2 electron-transport layer (ETL) is only 200 °C. The effect of Ga doping concentrations on the electric properties of Ga-TiO2 ETL and PSCs has been systematically investigated. At the optimum Ga concentration, the PSCs based on Ga-TiO2 and TiO2 ETL achieve the champion power conversion efficiency (PCE) of 17.09% and 14.63%, and an average PCE of 16.51% and 14.15%, respectively. The higher PCE of PSCs based on Ga-TiO2 ETL (Ga-PSCs) can be attributed to the reduced trap state density, enhanced conductivity, increased electron mobility and suppressed charge recombination, which will lead to higher Voc, Jsc and FF, thus the improved PCE. Moreover, the Ga-PSC shows negligible hysteresis and improved stability compared to the reference TiO2-PSC. After being stored in air for 28 days, the PCE of unsealed Ga-PSCs can remain to be 86% of its initial value. This work provides an excellent strategy to fabricate efficient and stable PSCs by low-temperature process.