Ultra-compact titanium oxide prepared by ultrasonic spray pyrolysis method for planar heterojunction perovskite hybrid solar cells

The electron transport layer of planar-heterojunction perovskite solar cells was produced by the ultrasonic spray pyrolysis (USP) of organotitanium precursors and the spin-coating of TiO2 sol-gel. Although the TiO2 products prepared from both methods have the same anatase crystal structure, the former route yields an ultra-compact, bulk-like film with reduced defects. Results from the electrochemical impedance spectroscopy measurements reveal the electron transfer resistance through the TiO2/CH3NH3PbIxCl3−x interface for the titanium oxide prepared by ultrasonic spray pyrolysis (TiO2-USP) method is lower than that for the titanium oxide prepared by sol-gel (TiO2-SG) method. Interesting, the TiO2-USP device exhibits relative low interfacial resistance of charge carrier through the CH3NH3PbIxCl3−x/spiro-OMeTAD interface as well. As a result, replacing TiO2-SG with TiO2-USP substantially improves the power conversion efficiency from 12.98% to 16.13%, demonstrating the USP is a facile approach to fabricate high-quality TiO2 for developing high-performance perovskite solar cells.