Effective Strategy to Improve Contact Selectivity in Organic Solar Cells

Improving the contact selectivity is an effective approach to reduce the non-radiative recombination voltage loss caused by charge carrier diffusion in organic solar cells. A surface modification strategy based on the use of the fullerene-selective solvent 1,8-diiodooctane (DIO) is proposed to improve the contact selectivity of organic solar cells. We observe that the fullerene molecules in the binary polymer–fullerene active layers or the ternary active layers containing both fullerene and non-fullerene acceptors are extracted to the surface after the DIO treatment. As a result, a dense fullerene layer, highly selective for electrons, is created at the cathode interface of the solar cell. The increased cathode selectivity gives rise to reduced diffusion loss of charge carriers, suppressed non-radiative recombination voltage loss, increased open-circuit voltage, and thus, the improved photovoltaic performance of the solar cell.