Carbon Nanosheets as Nanostructured Electrode in Organic Photovoltaic Devices

Photovoltaics, the direct conversion of sunlight into electric energy, is a promising clean-tech approach to energy production. Organic solar cells show particular promise because they have the potential for light-weight flexible devices with low material and production costs. Yet, despite significant improvements over the last couple of years, the maximum power conversion efficiency of organic photovoltaic devices is still about 5%, largely due to the low charge-carrier mobility in the organic materials. Low mobility increases resistance in the film, thereby reducing the photocurrent and the efficiency of the devices. This project aims to develop high efficiency, low-cost organic solar cells using novel nanostructured carbon electrodes consisting of free-standing carbon nanosheets. The volume between the sheets will be filled with photoactive material, thereby reducing the distance that charges have to travel to the collecting electrode. In Phase I, growth conditions for the carbon nanosheets were optimized for the organic photovoltaic application. An advanced spray coating technique was used to fill the nanosheets with photoactive material, and photovoltaic devices were built and tested. In addition, a technique was developed to transfer the nanosheets to a zero-thermal-budget substrate. Lastly, an atomic-layer-deposition process was developed to conformally coat the nanosheets with a dielectric interface layer. In Phase II, carbon nanosheet devices with superior photovoltaic performance will be demonstrated. A prototype device ¿ which will be compatible with a large-scale, roll-to-roll manufacturing process ¿ with commercially viable conversion efficiency will be built and characterized. Commercial Applications and Other Benefits as described by the awardee: Applications for the technology should range from rooftop photovoltaic systems to light weight, flexible solar cells integrated into tents, textiles, and small electronic devices (i.e. cell phones, PDAs, etc.). A successful commercialization also would help the economically challenged region of Southern Virginia transform its economy by opening new high-technology jobs.