Highly efficient inverted polymer solar cells using fullerene derivative modified TiO2 nanorods as the buffer layer

We reported a significant improvement in the efficiency of polymer solar cells by introducing C-60 pyrrolidine tris-acid (CPTA) to modify the interface between inorganic TiO2 nanorods and the organic active layer. The devices with CPTA-modified TiO2 as the cathode buffer layer exhibited a power conversion efficiency (PCE) as high as 8.74%, accounting for a 12.8% enhancement compared with the bare TiO2 based devices (7.75%) in the polymer thieno[3,4-b] thiophene/benzodithiophene:[6,6]-phenyl C-71-butyric acid methyl ester (PTB7:PC71BM) system. We found that the CPTA layer improves the surface properties of the bare TiO2 film so that charge transfer between the active layer and the TiO2 layer is enhanced.