Low temperature-processed ZnO nanorods-TiO2 nanoparticles composite as electron transporting layer for perovskite solar cells

Electron transport is one of the most crucial processes that determine charge collection efficiency in perovskite solar cells. Herein, a low temperature-processed ZnO-TiO2 nanocomposite is developed as an electron transporting layer for perovskite solar cells. Highly-crystalline ZnO nanorods were deposited electrochemically which served as the scaffold for spin-coated TiO2 nanoparticles. This ZnO-TiO2 nanocomposite is designed to integrate the fast electron transport along the nanorods and the additional surface area provided by the nanoparticles for enhanced electronic contact between the electron-transporting layer and the perovskite layer. A weak photoluminescence quenching behavior was observed for ZnO nanorods after TiO2 nanoparticle coating which signifies a reduction in ZnO surface defects. Steady-state photoluminescence and optical absorption measurements indicated improved charge transfer and higher absorption of light, respectively, when ZnO-TiO2 nanocomposite is contacted with the CH3NH3PbI3 layer. However, the clustering of the nanoparticles caused inefficient charge transfer from TiO2 to ZnO.