Energy Loss in Organic Solar Cells: Mechanisms, Strategies, and Prospects

Compared with conventional inorganic solar cells (ISCs), energy loss (E-loss) in organic solar cells (OSCs) is usually much higher, limiting their maximum achievable power conversion efficiency (PCE). In view of this, a hot topic in OSC research is how to make E-loss as low as possible. To date, in some typical organic donor/acceptor (D/A) blends, although E-loss has been reduced to the values comparable with those in ISCs, the PCEs of the corresponding devices still fails to meet expectations. One crucial issue is that the physics behind the photovoltaic process in these D/A blends and the corresponding energy loss remain unclear. Herein, combining with an analysis of the photovoltaic process in OSCs, the mechanisms of different energy loss pathways are first discussed. On this basis, the recent advances focusing on E-loss are systematically summarized according to different strategies: 1) optimizing the energy offset of the D/A blend; 2) optimizing the morphology of the D/A blend; 3) ternary modulation; and 4) spin modulation. Finally, the summary and prospects are presented, where some fundamental questions to be cleared up in the photovoltaic process are proposed, such that more targeted photovoltaic design can be carried out in the future investigations of OSCs.