Enhancement of VOC without Loss of JSC in Organic Solar Cells by Modification of Donor/Acceptor Interfaces

Organic solar cells (OSCs) are promising low-cost devices for generating electricity. In addition to fill factor, the short circuit current density (J(SC)) and the open circuit voltage (V-OC) are two key factors that have critical influence on the device performance. The energy levels of the donor and acceptor materials are crucial for achieving a high J(SC) and V-OC. However, the interfacial structures between the organic materials substantially affect the J(SC) and V-OC through the energy of the charge transfer (CT) states and the charge separation and recombination reaction kinetics. Here, it is reported that separating the donor and acceptor layer in bilayer OSCs with a thin insulating layer increases the energy of the CT state by weakening the Coulomb interaction at the interface and this also suppresses photoinduced CT and recombination. Although these effects usually increase V-OC and decrease J(SC), the trade-off is avoided by doping the insulating layer with a dye to utilize the energy transfer process. The increase in V-OC without the reduction in J(SC) enhances the conversion efficiency of the OSCs by 30%.