Enhanced efficiency of inverted polymer solar cells by using solution-processed TiO(x)/CsO(x) cathode buffer layer

In this work, a double-buffer film of TiO(x) coated with CsO(x) (TiO(x)/CsO(x)) was solution prepared to be applied in poly(3-hexylthiophene):indene-C(60) bisadduct (P3HT:ICBA) and P3HT:[6,6]-phenyl-C(61)-butyric acid methyl ester (PCBM) inverted polymer solar cells (PSCs). Compared with TiO(x) films and CsO(x) films, the TiO(x)/CsO(x) double-buffer film exhibited a favorable energy-level alignment among TiO(x), CsO(x), and the electron acceptor of PCBM or ICBA a better surface morphology; and an enhanced wetting and adhesion property with a contact angle of 21.0°, leading to a higher electron mobility of 5.52 × 10(−3) cm(2) V(−1)·s(−1). Moreover, the P3HT:ICBA and P3HT:PCBM photovoltaic devices with the double-buffer film showed the best power conversion efficiency up to 5.65% and 3.76%, respectively. Our results not only present that the double-buffer film is superior than the single film of TiO(x) and CsO(x), but also imply that the solution-processed film has a potential to be generally used in roll-to-roll processed organic photovoltaic devices.