Theoretical study of the open circuit voltage decay on Organic Photovoltaic (OPV) solar cells based on space radiation ionizing damage

Abstract

Organic photovoltaic (OPV) solar cells have progressed quite significantly as an affordable energy technology, with high-throughput roll-to-roll solution processing driving down costs to the point of competitiveness with current technologies. They potentially offer significant advantages over classical inorganic semiconductor cells; specifically, down costs, lightness, flexibility and controlled donor-acceptor film composition. Our specific interest is based on the applicability of organic photovoltaics cells for use in space based solar panels. The present work is a theoretical study of ionizing radiation effects in the organic photovoltaic structure P3HT: PCBM for total accumulated doses up to 1kGy (SiO2). We find that the open circuit voltage (Voc) varies with the accumulation of irradiation; however, other parameters such as relaxation time, short circuit current, and charge carrier density remain to first order constant. At the interface, the energetic mismatch of the molecular orbitals provides enough driving force to split the exciton in order to create free charge carriers (an electron (e-) and the corresponding hole (h+)). This is consistent with observations on preirradiation cases that depend directly on the Voc, due to carriers and quasi states; this leads to a linear recombination according to the Dose Damage Displacement (Dd) and Non-Ionizing Energy Loss (NIEL). Finally, we conclude that the organic photovoltaics will survive in a space environment up to 1 kGy (SiO2), contrary to popular belief that organics would be radiation “soft.”