Enhancing the Photo-oxidative Stability of Non-Fullerene Electron Acceptors

Abstract

Abstract: Even though improvements in the efficiency of organic solar cells encouraged the commercialization of this technology in the past two decades, the stability of organic solar cells is still an active area of research. The effect of photo-oxidative degradation on the performance of organic solar cell devices is significant. One way to lower the rate of photooxidation degradation is by preventing oxygen molecules from reaching the active layer of organic solar cells. This could be achieved by fabricating the devices in an inert environment in the absence of oxygen. Once the devices are fabricated, they would be encapsulated in a transparent material.1, 2 Even though this is a viable solution, there are two main issues. First, it was shown that oxygen molecules could diffuse through the encapsulating material and degrade the devices.3 Second, implementing this solution would increase the fabrication cost of these devices, which would make this solution commercially unfeasible compared to other solar cell technologies.3 Speller and his colleges reported a possible mechanism of the photo-oxidative degradation and showed a relationship between the rate of degradation and LUMO energy levels of electron acceptor molecule4. In this thesis, we report the photo-oxidative degradation rate of O-IDTBR and O-IDTBR-(C3N2)2. The later electron acceptor is analogous to O-IDTBR with deeper LUMO by 0.1 eV. After four hours of constant irradiation from a 1-sun intensity xenon solar simulator, the maximum UV-Vis absorbance of O-IDTBR is reduced by 12% relative to O-IDTBR-(C3N2)2. Lower absolute degradation rates were observed when 1-sun LED solar simulator was used compare to xenon solar simulator.