ZnO-Assisted Growth of CH3NH3PbI3-xClx Film and Efficient Planar Perovskite Solar Cells with a TiO2/ZnO/C60 Electron Transport Trilayer

Appropriate electron transport layers (ETL) are essential in perovskite solar cells (PSCs) with high power conversion efficiency (PCE). Herein, a TiO2/ZnO/C-60 trilayer fabricated on a transparent fluorine-doped tin oxide (FTO) glass substrate is used as a compound ETL in planar PSCs. The trilayer shows positive effects on both perovskite synthesis and device performance. The ZnO layer assists growth of CH3NH3PbI3-xClx (x approximate to 0) annealed at a lower temperature and with a shorter time, which is due to a more rapid and easier decomposition of the intermediate CH3NH3PbCl3 phase in the growth of CH3NH3PbI3-xClx. All three materials in the trilayer are important for obtaining PSCs with a high PCE. ZnO is critical for enhancing the open circuit voltage by ensuring proper energy alignment with the TiO2 and C-60 layers. C-60 enhances carrier extraction from the CH3NH3PbI3-xClx layer. TiO2 eliminates charge recombination at the FTO surface and ensures efficient electron collection. The best-performing PSC based on the TiO2/ZnO/C-60 electron transport trilayer features a PCE of 18.63% with a fill factor of 79.12%. These findings help develop an understanding of the effects of ZnO-containing ETLs on perovskite film synthesis and show promise for the future development of high-performance PSCs with compound ETLs.