Device characteristics of CuPc/TiO2 heterojunctions

An abrupt junction exists at the CuPc/ TiO₂ heterojunction of Au/CuPc/TiO₂/InSnO₂ cells. A transparent n-TiO₂ film has been deposited onto ITO glass substrate using the sol-gel technique. Copper phthalocyanine (CuPc) is subsequently vacuum sublimed onto the TiO₂ surface. The junction is 0.32 V high at the zero-bias potential and at room temperature. Conduction is mainly due to the diffusion of majority carriers, but the ideality factor slightly greater than unity implies the presence of a small recombination current. Photoelectrical measurements are carried out under simulated solar radiation and within a wavelength range of 300-900 nm. It is found that the photogeneration reaches its maximum efficiency at 350 nm in air. The value of the fill factor lies between 0.2 and 0.3, depending on the age of the cells. This low value, which may be attributed to a large series resistance arising from the low conductivity of the CuPc film, suggests that film much thinner than 460 nm would improve the efficiency