Impact of Ozone Exposure on OPV Efficiency
Organic solar cells are a considerable promise for alternate energy sources owing to their plentiful, easily accessible and renewable source of power. Degradation on organic film and anode layer are the major factors that determine device reliability and ozone can induce damage to these materials due to its strong oxidizing property. This study measured the sustainability of a type of organic photovoltaic (OPV) film (P3HT:PC71BM) and its anodes (Al and MoO3) to different levels of ozone environment and investigated the impact of ozone exposure on OPV film and anodes efficiency. The devices were fabricated in a Glove Box under controlled N2 atmosphere using Spin Coating and Physical Vapor Deposition and exposed to varied ozone concentrations, followed by J-V measurements to determine the Power Conversion Efficiency and Fill Factor. The effects of ozone exposure on the films were compared vs. the effects of exposure on complete devices with anodes (Al and MoO3). The results show that the devices decay from normal efficiency (4%) to 0% in 12 hours under 300 ppb (ï¿½10%) ozone concentration and decay to 0% in 6 hours when the ozone concentration was 600 ppb (ï¿½10%), when only the polymer thin films are exposed. This established an inverse linear relationship between the decay rate and ozone exposure at high concentrations on the OPV films. Furthermore, the effect of exposure to ambient ozone concentration on the polymer films, which is 70 ppb (ï¿½15%), was also investigated and the devices were found to decay to 0% in 28 hours, which is much faster than expected. The decay resistance of complete devices when the polymer films are coated with thermally evaporated anodes (Al and MoO3) before exposure to 400 ppb ozone concentration was investigated. The average efficiency of the complete device after 2, 6, 10, 15, 28 and 42 hours exposure in 400 ppb ozone environment was 4.16% with a standard deviation of 0.12%. The test findings for the complete device with coated anodes show that the current design of the complete OPV device has good resistance to ozone oxidation without additional protection or encapsulation. This finding has significant bearing with respect to the selection and price of encapsulation material requirements for OPV. This research work is a part of a project funded by the National Science Foundation (Grant # CHE – 1230598) on the SEP Collaborative: Development of economically viable, highly efficient organic photovoltaic solar cells.