Dual Förster Resonance Energy Transfer Effects in Non-Fullerene Ternary Organic Solar Cells with the Third Component Embedded in Donor and Acceptor
Non-fullerene ternary organic solar cells (OSCs) are new promising candidates for future application in the area of organic photovoltaics. However, the low short-circuit current (JSC) is still the limitation of pursuing higher power conversion efficiency (PCE). Maximizing the JSC is one of the critical elements toward enabling high performance of OSCs. To improve the JSC of the non-fullerene ternary OSCs based on poly[[2,6′-4,8-di(5-ethylhexylthienyl)benzo[1,2-b;3,3-b] dithiophene] [3-fluoro-2[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]]：3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone) -5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]-dithiophene (ITIC) (PTB7-Th:ITIC), a polymer of poly[N-9''-hepta-decanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole) (PCDTBT) is introduced into the binary system. It is proved that PCDTBT is embedded in both PTB7-Th and ITIC introducing dual Förster Resonance Energy Transfer (FRET) effects in the ternary system. In addition, the PCDTBT may decrease the molecular coherent lengths of PTB7-Th and ITIC and influence the charge transport. Furthermore, the PCDTBT can also decrease the d-spacing of π-π stacking of PTB7-Th and ITIC, which can increase the intermolecular charge hopping efficiency. With appropriate amount of PCDTBT doping in the system, the JSC can increase from 13.89 to 16.71 mA cm-2. The increased JSC results in an enhancement of PCE by 15%, which indicates that introducing dual FRET effects is an effective way to enhance the JSC and thus the performance of the OSCs.