Copper nanowire-TiO₂-polyacrylate composite electrodes with high conductivity and smoothness for flexible polymer solar cells

Copper nanowire (Cu NW) transparent electrodes have attracted considerable attention due to their outstanding electrical properties, flexibility and low cost. However, complicated post-treatment techniques are needed to obtain good electrical conductivity, because of the organic residues and oxide layers on the surface of the Cu NWs. In addition, commonly used methods such as thermal annealing and acid treatment often lead to nanowire damage. Herein, a TiO₂ sol treatment was introduced to obtain Cu NW transparent electrodes with superb performance (13 Ω/sq @ 82% T) at room temperature within one minute. Polymer solar cells with excellent flexibility were then fabricated on the copper nanowire-TiO₂-polyacrylate composite electrode. The power conversion efficiency (PCE) of the cells based on a blend of poly(3-hexylthiophene) (P3HT) and phenyl-C₆₁-butyric acid methyl ester (PC₆₁BM) reached 3.11%, which was better than the control devices that used indium tin oxide (ITO)-PET electrodes, and outperforms other Cu NW based organic solar cells previously reported. The PCE of the solar cells based on Cu NW electrodes remained at 90% after 500 cycles of bending, while the PET/ITO solar cells failed after 20 and 200 cycles, with sheet resistance of 35 and 15 Ω/sq, respectively.