Simple solution-processed titanium oxide electron transport layer for efficient inverted polymer solar cells

• High quality s-TiOX films were prepared by a simple, solution method without thermal treatment.
• The s-TiOX films with high transmittance are very smooth.
• The organic photovoltaic performance with s-TiOX film improved greatly and exhibited good stability.
• The annealing-free, simple prepared s-TiOX film will be much compatible with flexible substrates.

Titanium oxide (TiOX) is an effective electron transport layer (ETL) in polymer solar cells (PSCs). We report efficient inverted PSCs with a simple solution-processed amorphous TiOX (s-TiOX) film as an ETL. The s-TiOX film with high light transmittance was prepared by spin-coating titanium (IV) isopropoxide isopropanol solution on indium tin oxide coated glass in inert and then placed in air under room temperature for 60 min. The introduction of s-TiOX ETL greatly improved the short circuit current density of the devices. PSCs based on poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester and poly(4,8-bis-alkyloxy-benzo[1,2-b:4,5-b′]dithiophene-alt-alkylcarbonyl-thieno[3,4-b]thiophene):[6,6]-phenyl- C71-butyric acid methyl ester using s-TiOX film as ETL shows high power conversion efficiency of 4.29% and 6.7% under the illumination of AM 1.5G, 100 mW/cm2, which shows enhancements compared to the conventional PSCs with poly(styrenesulfonate)-doped poly(ethylenedioxythiophene) as anode buffer layer. In addition, the device exhibits good stability in a humid ambient atmosphere without capsulation. The results indicate that the annealing-free, simple solution processed s-TiOX film is an efficient ETL for high-performance PSCs.