The photovoltaic mechanism of a polythiophene/perylene pigment two-layer solar cell

The energy conversion efficiency of a two-layer organic solar cell consisting of a perylene pigment (PV) and regioregular polythiophene polymer (P3DT) was 0.99% under illumination with Simulated solar light (AM 1.5-100 mW cm(-2)). The photovoltaic mechanism is discussed on the basis of the ionization potential of the component materials. The photoinduced hole-transfer from PV to P3DT quickly occurred at the PV/P3DT interface because of the large free energy change of 1.2 eV, then the subsequent charge separation efficiently proceeded, resulting in a large short-circuit photocurrent of 6.5 mA cm(-2). On the other hand, the open-circuit photovoltage was only 0.42 V because the LUMO level of PV is close to the HOMO level of P3DT. The difference between the LUMO and the HOMO can be attributed to the open-circuit photovoltage.