Influence of codeposition on the performance of CuPc–C60 heterojunction photovoltaic devices

We investigate the effects of introducing codeposited mixed layers on the performance of copper phthalocyanine (CuPc)–fullerene (C60) heterojunction photovoltaic devices. Significant improvements in device performance are seen when mixed layers are used compared to discrete layers. The effects of composition are examined for a series of devices incorporating mixed layers with well-defined composition ratios. Atomic force microscopy and electronic absorption spectroscopy studies show that the mixed layer films are smooth and amorphous, and undergo intermolecular intermixing. Finally, the use of multiple mixed layers leads to additional enhancements due to the creation of a gradient of donor–acceptor compositions that results in improved channels for charge transport.