Temperature dependent behavior of flat and bulk heterojunction organic solar cells

The open-circuit voltage of an organic solar cell is increasing with decreasing temperature and with increasing illumination intensity. These dependencies are quantitatively investigated for two types of organic solar cells, one with a flat donor-acceptor heterojunction and one with a mixed layer bulk heterojunction. Zinc-phthalocyanine and C60 are used as donor and acceptor, respectively. A qualitative difference is found for the two geometries. We find that a logarithmic illumination intensity dependence with temperature as a linear pre-factor of the logarithm, which is commonly reported and observed, is applicable for the bulk heterojunction. The flat heterojunction, in contrast, shows a constant illumination intensity pre-factor which is independent of the temperature, and the temperature can be modeled as additional linear summand. © 2013 Materials Research Society