Comparative analysis of burn-in photo-degradation in non-fullerene COi8DFIC acceptor based high-efficiency ternary organic solar cells
The ternary organic solar cell is a promising technology towards high power conversion efficiency. Although the efficiency has reached over 14% for ternary organic solar cells, the stability, as well as the degradation mechanism behind the ternary strategy, are still not well investigated. Burn-in photo-degradation, which is caused by continuous light illumination, can result in a significant performance drop at an initial stage for solar cells. COi8DFIC is a newly developed efficient non-fullerene acceptor material that exhibits strong near infrared range (NIR) light absorption. Herein, we present the first systematic research on the burn-in photo-degradation of a COi8DFIC based ternary organic solar cell with the active layer consisting of PTB7-Th:COi8DFIC:PC71BM blend and compared it with its corresponding binary organic solar cells. Both binary and ternary devices were exposed to continuous one-sun illumination for 5 hours. As a result, PTB7-Th:COi8DFIC based binary and ternary organic solar cells exhibit a similar degradation mechanism which is very different from the burn-in photo-degradation mechanism in PTB7-Th:PC71BM based binary organic solar cells. The burn-in photo-degradation in PTB7-Th:PC71BM binary organic solar cells is found to be dominated by induced non-radiative carrier recombination, poor energy transfer and low exciton dissociation. However, the burn-in photo-degradation in PTB7-Th:COi8DFIC based binary and ternary organic solar cells is found to be more related to the degradation-induced high shunt possibility.