Irradiation tolerance of an optically transparent polyimide film under 1 MeV electron beam

As ideal encapsulation materials for thin-film space solar cells, optically transparent polyimide (PI) films are required to withstand harsh space environments. Herein, we investigate the irradiation tolerance of an optically transparent polyimide film with tert-butyl, cyclohexyl and trifluoromethyl groups under 1 MeV energy electron beam. After irradiation, the PI film still not only maintains excellent optical transparency (the average transmittance decreased negligibly only from 87% to 86% in the visible light region (400–760 nm)) , but also keeps good thermal stability (the temperature at 5% weight loss in N2 atmosphere (T5%) was 442 °C), high glass transition temperature (340 °C, by DMA), and good mechanical properties (tensile strength: 71.3 MPa, Young’s modulus: 1.13 GPa, elongation at break: 7.7%). To understand the mechanism of irradiation damage, the bulk and surface performances of the PI film before and after irradiation were systematically investigated by various characterization methods. The results indicate that the surface of the PI film had a slight damage by 1 MeV electron irradiation, but its structure was nearly kept intact. Such a PI film has super irradiation resistance and is a potential candidate as encapsulating materials for space solar cells.