Ultimate efficiency of polymer/fullerene bulk heterojunction solar cells

We present model calculations to explore the potential of polymer/fullerene bulk heterojunction solar cells. As a starting point, devices based on poly(3-hexylthiophene) and 6,6-phenyl ${\mathrm{C}}_{61}\text{-}\mathrm{butyric}$ acid methyl ester (PCBM), reaching $3.5\%$ efficiency, are modeled. Lowering the polymeric band gap will lead to a device efficiency exceeding $6\%$ . Tuning the electronic levels of PCBM in such a way that less energy is lost in the electron transfer process enhances the efficiency to values in excess of $8\%$ . Ultimately, with an optimized level tuning, band gap, and balanced mobilities polymeric solar cells can reach power conversion efficiencies approaching $11\%$ .