Flexible inverted polymer solar cells containing an amorphous titanium oxide electron collection electrode

An inverted polymer solar cell was fabricated on a polyethylene terephthalate (PET) substrate. The cell structure was ITO/amorphous titanium oxide (TiOx)/[6,6]-phenyl C61 butyric acid methyl ester (PCBM): regioregular poly(3-hexylthiophene) (P3HT)/poly(3,4-ethylenedioxylenethiophene):poly(4-styrene sulfonic acid) (PEDOT:PSS)/Au (TiOx cell). It was achieved using low boiling point diethyl amine (DEA) as a Ti4+ complexing agent, and high boiling point 1,2,3,4-tetrahydronaphthalene (Tetralin) containing 2 vol.% 1,8-octanedithiol (ODT) as the solvent for PCBM:P3HT film preparation. With heat treatment at 100 °C, the use of DEA and Tetralin:ODT made it possible to prepare a TiOx electron collection layer and PCBM:P3HT photoactive layer, respectively. Fabricating the TiOx cell on the thin PET film was possible, as PET did not warp at 100 °C. The power conversion efficiency (PCE) of the TiOx cell fabricated on PET was 2.43%, under AM1.5G conditions. When fabricated on glass, the PCE was 2.76%. When [6,6] diphenyl C62 bis(butyric acid methyl ester) (bis-PCBM) was instead used as the electron acceptor in the photoactive blend layer, the flexible air-stable cell provided a PCE of 2.81%.

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► Inverted polymer solar cells were fabricated on PET substrate.
► PET-ITO/amorphous TiOx/PCBM:P3HT/PEDOT:PSS/Au type cell showed the power conversion efficiency (PCE) of 2.43%.
► In addition, PET-ITO/amorphous TiOx/bis-PCBM:P3HT/PEDOT:PSS/Au type cell exhibited the PCE of 2.81%.