The study on the transport efficiency of effective excitons and relationship with the thickness of active materials

Organic solar cells are attracting a great deal of attention now. However, the academic system of organic solar cells is still not so perfect. Most analysis of exciton recombination was still on the qualitative process. In this paper, a concept of effective exciton transport efficiency was given, based on the generation rate of effective excitons. Using this method, the error between the simulation of effective exciton generation rate and practical experiments was explained more clearly. With the increase of the active layers' thicknesses, the electrode interface would leave farther away from the effective exciton generation region. This made less influence of electrode interface to the effective excitons, and the transport efficiency increased. Although this decreased the effective exciton generation rate a little, the performances of cells still can get better. The transport efficiency also can explain the function of electrode buffer layers, as well as the superiority of C-70 acceptor to that of C-60.