Fast Nonradiative Decay Paths in Organic Solar Cells: Implications for Designing More Efficient Photovoltaic Systems

With the aim of understanding the sources of energy losses in bulk heterojunction solar cells, the rates of elementary charge-transfer processes occurring at the donor-acceptor interface have been determined by employing a combined classical and quantum mechanical approach for four prototypical blends, covering a wide range of power conversion efficiency values. The results show that backward electron transfer from the charge-transfer state at the D/A interface to the ground state is a fast process, which can efficiently compete with charge dissociation; indeed, a clear-cut correlation between the rates of nonradiative charge recombination and the observed power conversion efficiency has been found. The finding presented above suggests important criteria for the rational design of acceptor-donor blends for organic photovoltaics.