Origin of the open circuit voltage in conjugated polymer-fullerene photovoltaic cells

摘要

We fabricated polymer-fullerene photovoltaic (PV) devices using various conjugated polymers, poly[2-methoxy-5-(2'-ethylhexyloxy)-1, 4-phenylenevinylene] (MEH-PPV), poly[2-{4-(3,7-dimethyloctyloxy)-phenoxy}-1, 4- phenylenevinyl-ene] (p-DMOP-PPV), and their copolymer system, p-DMOP-co-MEH-PPV. By comparing PV characteristics of such devices with a systematic change of the energy levels (ionization potential I_p and electron affinity E_a), we investigated the origin of open circuit voltage (V_(oc)) of the devices. Our results indicate that the magnitude of V_(oc) is governed by the difference between E_a of the fullerene and I_p of the polymer, which is not consistent with previous consideration of the work function difference between electrodes as in conventional metal-insulator-metal type devices.