Thermally assisted charge transfer and charge separation in organic donor-acceptor solar cells

Abstract

We propose a mechanism based on thermally assisted charge transfer (CT) to study the thermal effect on the formation of CT states and subsequent charge separation in an organic donor-acceptor solar cell. We reveal that the difference between phonons in the donor and acceptor caused by elastic energy acts as a thermally assisted driving force for charge transfer. It is found that the system exhibits a quite different CT process in the high and low temperature regions. Remarkably, combined with the entropy driving mechanics, the thermally assisted CT yields charge separation probability as high as 70% at room temperature. Our model and results provide a microscopic quantum understanding of the relevant recent experiments and open up a route to realize high-efficiency organic solar cells by effectively taking advantage of the thermal effect.