Enhanced Perovskite Solar Cells with Cesium-Doped TiO2 Compact Layer

In perovskite solar cells, interfacial engineering is one of the keys to promote cell efficiencies. In this work, a cesium-doped TiO2 (Cs-doped TiO2) compact layer is introduced by a simple sol-gel method into planar-structure perovskite solar cells. Mott-Schottky (M-S) plot measurements revealed that the Cs-doping caused a 0.113 V negative shift of flat-band potential, which resulted in an up-shift of Fermi-level of TiO2 compact layer. Since CH3NH3PbI3-xClx perovskite morphology was not changed with a Cs-doped compact layer confirmed as SEM images and UV-Vis spectra, the corresponding increment of cell open-circuit voltage (V-oc) for about 0.1 V is mainly attributed to CBM up-shift, with the short-circuit current density (J(sc)) loss negligible compensated by the enhanced compact layer conductivity of Cs-doping. Electrochemical Impedance Spectroscopy (EIS) measurement also confirms the enhanced performance with retarded recombination at the interface and decreased series resistance. The best efficiency reached 6.72% with P3HT as the hole transporting material, in contrast to 6.18% for the un-doped ones.