Spray deposited lanthanum doped TiO2 compact layers as electron selective contact for perovskite solar cells

TiO2 compact layers are wildly used for electron selective contact in perovskite solar cells. The function of TiO2 selective contact can be modified by doping metal ions in the TiO2 compact layers. As lanthanide elements usually exhibit unique properties for their incompletely occupied 5d or 4f orbitals, we prepared lanthanum doped TiO2 compact layers by spray pyrolysis method as the electron selective contact of perovskite solar cells. SEM images indicate lanthanum dopants improve the smoothness of TiO2 layers. In the optimized concentration, the average PCE of devices is promoted from 12.4% to 14.4% with the highest PCE of 17.2%, which comes from the improvement on charge transfer and recombination. Moreover, the Lanthanum dopants also lead to the improvement in photo-stability of perovskite solar cells. For the device with optimized La concentration, 80% of its original PCE is preserved after 200 h aging under continuous one sun illumination.