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 C₆₀ 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 C₇₁-butyric acid methyl ester (PTB7:PC₇₁BM) system. We found that the CPTA layer improves the surface properties of the bare TiO ₂ film so that charge transfer between the active layer and the TiO₂ layer is enhanced.