Temperature dependence for the photovoltaic device parameters of polymer-fullerene solar cells under operating conditions

We report on the temperature dependence of various photovoltaic device para meters of solar cells, fabricated from interpenetrating networks of conjuga ted polymers with fullerenes, in the wide temperature range of their possib le operating conditions (25-60 degreesC). The open-circuit voltage was foun d to decrease linearly with increasing temperature. For the short-circuit c urrent, we observed a monotonic increase with increasing temperature, follo wed by a saturation region. The rate of this increase (coupled to a corresp onding increase for the fill factor) was found to overtake the correspondin g rate of decrease in voltage, resulting in an overall increase of the ener gy conversion efficiency. The efficiency was observed to reach a maximum va lue in the approximate range 47-60 degreesC. The results are discussed with respect to possible mechanisms for photovoltage generation and charge carr ier transport in the conjugated polymer-fullerene composite, and in particu lar, thermally activated charge carrier mobility. (C) 2001 American Institu te of Physics.