Fundamental Flaw in the Current Construction of the TiO2 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 TiO2 electron transport layer (ETL). However, the efficacies and stability of the current stereotypically prepared TiO2 ETLs employing commercially available TiO2 nanocrystal paste are far from their maximum values. As revealed herein, the long-hidden reason for this discrepancy is that acidic protons (similar to 0.11 wt %) always remain in TiO2 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/TiO2 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 TiO2 nanocrystal paste precursor and replicated the high-temperature sintering process, which wiped out nearly all protons in TiO2 ETLs during the sintering process. The use of deprotonated TiO2 ETLs not only promotes the PCE of both MAPbI(3)-based and FA(0.85)MA(0.15)PbI(2.55)Br(0.45)-based devices over 20% but also significantly improves the long-term photostability of the target devices upon 1000 h of continuous operation.

Automated summary

The study uncovers the issue of acidic protons residue in TiO2 ETL prepared with commercially available TiO2 nanocrystal paste, and proposes a straightforward deprotonation approach to eliminate this issue. This method significantly enhances the performance and stability of perovskite solar cells.