Tuning the Pore Structures in TiO2 Thin Films by Polymer Templates for High-Performance Perovskite Solar Cells

Increasing the contact area between TiO2 thin films (TFs) and methylammonium lead iodide (MAPbI3) perovskite layers (PLs) is important to improving the electron transport in perovskite solar cells (PSCs). We fabricated various PSCs incorporated with mesoporous TiO2 (meso-TiO2) TFs comprising an organic polymer (i.e., ethylcellulose (EC)) as a templating agent to increase the contact area of TiO2 with MAPbI3. The average pore size and thickness of the meso-TiO2 TFs/MAPbI3 PLs are controlled by varying the amount of EC in the TiO2 TFs. The as-prepared meso-TiO2 enhances the crystallinity and infiltration of MAPbI3 PLs and passivates several defects formed at the interfaces of the TiO2 TFs and MAPbI3 PLs. An optimized EC-templated meso-TiO2 TF applied as an electron transport layer in PSCs exhibited a maximum power conversion efficiency (PCE) of 16.64%, which was substantially higher than that obtained by using a pristine TiO2 layer (PCE = 11.32%) as the reference device. This suggests that the use of commercially available polymer templates can significantly aid the development of highly efficient PSCs incorporated with mesostructure-tuned TiO2 TFs and MAPbI3 PLs fabricated by using a relatively simple, viable, and low-cost spin-coating method.