Correlation between LUMO offset of donor/acceptor molecules to an open circuit voltage in bulk heterojunction solar cell

The correlation between the open circuit voltage and the LUMO offset of the donor and acceptor polymers in the bulkheterojunction solar cell was studied for three different thiophene derivatives. The HOMO levels of all the polymers in this investigation were chosen to be similar which results in close values of ΔEDA=EHOMOD−ELUMOA. However, the measured VocVoc was found to be increasing with decreasing value of the LUMO offset that exists between the donor polymer and fullerene.