Open Circuit Voltage of Organic Photovoltaic Cells using Free Acceptor

Organic solar cells are based on a couple of organic materials, one is called electron donor and the other electron acceptor. Usually the acceptor is the fullerene. However if it is an efficient electron conductor, it absorbs weakly the light and its contribution to the current is small. Therefore, in the present work we study couples where the acceptor is SubPc, AlPcCl, DTPMM or DBP. These molecules have been chosen as electron acceptor because their band structure is compatible with such use. The study shows that the band offset value between the electron donor and the electron acceptor must be higher than the exciton energy, whatever the distribution between the bands. Moreover, it is shown that, if a sufficient band offset value is necessary, it is also necessary that the molecule proposed as electron acceptor must have a sufficient electron mobility, i.e., the molecule must be ambipolar. On the other hand the electron donor layer must be smooth and must exhibit a sufficient hole mobility.