Correlation between nanoscale surface potential and power conversion efficiency of P3HT/TiO2 nanorod bulk heterojunction photovoltaic devices

This is an in depth study on the surface potential changes of P3HT/TiO2 nanorod bulk heterojunction thin films. They are affected by interlayer structures, the molecular weight of P3HT, the processing solvents and the surface ligands on the TiO2. The addition of an electron blocking layer and/or the hole blocking layer to the P3HT/TiO2 thin film can facilitate charge carrier transport and result in a high surface potential shift. The changes in surface potential of multilayered bulk heterojunction films are closely correlated to their power conversion efficiency of photovoltaic devices. Changing ligand leads to the largest change in surface potential yielding the greatest effect on the power conversion efficiency. Merely changing the P3HT molecular weight is less effective and varying the processing solvents is least effective in increasing power conversion efficiency. The steric effect of the ligand has a large influence on the reduction of charge carrier recombination resulting in a great effect on the power conversion efficiency. By monitoring the changes in the surface potential of bulk heterojunction film of multilayer structures, we have obtained a useful guide for the fabrication of high performance photovoltaic devices.