Structural Defects in Donor-Acceptor Blends: Influence on the Performance of Organic Solar Cells

The performance of organic solar cells is limited by trap states, which increase energetic disorder, lead to trap-assisted recombination of charge carriers, and lower carrier mobility. To increase solar-cell efficiency, it is important to understand the origin and energetic distribution of those states. Using impedance spectroscopy, the authors find that the intermixing of C${}_{60}$ and the donor molecule DCV5T-Me in bulk heterojunction solar cells introduces notably deep electron-trap states in the C${}_{60}$ phase, decreasing power-conversion efficiency. As C${}_{60}$ is a widely used acceptor material, these findings are of general interest for fullerene-based solar cells.