Bilayer molecular solar cells on spin-coated TiO2 substrates

Solar cells with 20 nm films of molecular semiconductors can be constructed without electrical shorts by depositing the organic layers onto spin-coated films of TiO2. The photovoltaic characteristics of a bilayer cell consisting of perylene bis(phenethylimide) and zinc phthalocyanine were measured and compared to those of the individual layers. The bilayer was much more efficient than either individual monolayer but did not behave as a classical p-n junction. It exhibited a short circuit photocurrent density of 1.5 mA/cm2 and a wavelength-averaged short circuit quantum yield of 18% under 1 sun conditions.