Improving poly(3-hexylthiophene)-TiO2 heterojunction solar cells by connecting polypyrrole to the TiO2 nanorods

•A heterojunction solar cell is prepared from poly (3-hexylthiophene) and the purposely surface-modified TiO2 nanorod array.•The modification is carried out by connecting polypyrrole to the TiO2 array through an in-situ photopolymerization.•The photovoltaic performances of the device are improved due to the surface modification.•The function of polypyrrole in the device is investigated by using electrochemical and intensity modulated photovoltage spectroscopes.

A heterojunction solar cell is prepared from poly(3-hexylthiophene) (P3HT) and the purposely surface-modified TiO2 nanorod array. The modification is carried out by connecting polypyrrole (PPy) to the TiO2 nanorod array through an in-situ polymerization, which is initiated by photoexcited TiO2 nanorods. The as-prepared composite films are investigated by using photoluminescence emission spectroscopy, electrochemical impedance spectroscopy and intensity modulated photovoltage spectroscopy. The analysis results demonstrate that modifying TiO2 nanorod array with PPy increases the efficiency of charge separation and prolongs the electron lifetime. It is observed that the modified P3HT/PPy/TiO2 solar cell shows the power conversion efficiency which is 77% higher than that of the P3HT/TiO2 solar cell. These results prove that the in-situ photopolymerization is an efficient method to modify for the heterojunction solar cell.