Electrical aspects of operation of polymer-fullerene solar cells

Easily processable conjugated polymers for optoelectronics, in general, and for photovoltaic energy conversion, in particular, is an attractive research field, in which the combined efforts of material science, device engineers, and spectroscopists are welcomed. To improve the efficiency of polymer solar cells, it is vital to understand which mechanisms control the current-voltage characteristics of a given device. The current-voltage characteristics of ITO/PEDOT:PSS/OC1C10-PPV:PCBM/Al solar cells were measured in the temperature range 120-320 K under variable illumination, between 0.03 and 100 MW/cm(2) (white light). The short circuit current density grows monotonically with temperature until 320 K. This is indicative of a thermally activated transport of photogenerated charge carriers, influenced by recombination with shallow traps. A gradual increase of the open circuit voltage to 0.91 V was observed upon cooling the devices down to 120 K. The overall effect of temperature on solar cell parameters results in a positive temperature coefficient of the power conversion efficiency, which is 1.9% at T=320 K and 100 mW/cm(2). The nearly linear variation of the short circuit current density with light intensity confirms that the internal recombination losses are predominantly of a monomolecular type under short circuit conditions. 2003 Elsevier B.V. All rights reserved.