Realization of large area flexible fullerene - Conjugated polymer photocells: A route to plastic solar cells

Bulk donor - acceptor heterojunctions between conjugated polymers and fullerenes have been utilized for photovoltaic devices with quantum efficiencies of around 1%. These devices are based on the photoinduced, ultrafast electron transfer between non degenerate ground state conjugated polymers and fullerenes. In this work we present efficiency data of solar cells based on a soluble alkoxy poly(para phenylenevinylene) (MDMO-PPV) and a highly soluble fullerene derivative (PCBM). Small area (mm(2)) photovoltaic devices show energy conversion efficiencies eta(e) > 1% and charge carrier collection efficiencies eta(c) similar to 20%. We present efficiency and stability studies on large area (6 cm x 6 cm) flexible solar cells and compare them with small area devices. The process of large scale coating using printing techniques demands excellent rheological properties of the solution and the compound. We studied the influence of conventional polymers as additives for the photoactive compounds in order to improve homogenous film formation. Addition of small amounts (11 wt%) of conventional polymers does not alter the device characteristics. At higher concentrations of additives conversion efficiency drop down quickly.