Fundamental Flaw in the Current Construction of the TiO Electron Transport Layer of Perovskite Solar Cells and Its Elimination.

The top-performing perovskite solar cells (efficiency > 20%) generally rely on the use of a nanocrystal TiO electron transport layer (ETL). However, the efficacies and stability of the current stereotypically prepared TiO ETLs employing commercially available TiO nanocrystal paste are far from their maximum values. As revealed herein, the long-hidden reason for this discrepancy is that acidic protons (∼0.11 wt %) always remain in TiO ETLs after high-temperature sintering due to the decomposition of the organic proton solvent (mostly alcohol). These protons readily lead to the formation of Ti-H species upon light irradiation, which act to block the electron transfer at the perovskite/TiO interface. Affront this challenge, we introduced a simple deprotonation protocol by adding a small amount of strong proton acceptors (sodium ethoxide or NaOH) into the common TiO nanocrystal paste precursor and replicated the high-temperature sintering process, which wiped out nearly all protons in TiO ETLs during the sintering process. The use of deprotonated TiO ETLs not only promotes the PCE of both MAPbI-based and FAMAPbIBr-based devices over 20% but also significantly improves the long-term photostability of the target devices upon 1000 h of continuous operation.