Förster resonance energy transfer in p-DTS(FBTTh2)2- p-SIDT(FBTTh2)2 small molecule ternary blend bulk-heterojunction solar cells for enhanced power conversion efficiency

Abstract In this study, we demonstrate a new all small molecule ternary bulk heterojunction (BHJ) organic solar cells (OSCs) incorporating two small molecule (SM) (7,7′-[4,4-Bis(2-ethylhexyl)-4H-silolo[3,2-b:4,5-b′]dithiophene-2,6-diyl]bis[6-fluoro-4-(5′-hexyl-[2,2′-bithiophen]-5yl)benzo [c][1,2,5] thiadiazole] (p-DTS(FBTTh 2 ) 2 ) and benzo [1,2-b:4,5-b]bis (4,4′-dihexyl-4H-silolo[3,2-b]thiophene-2,2′-diyl)bis(6-fluoro-4-(5′-hexyl-[2,2′-bithiophene]-5-yl)benzo[c][1,2,5] thiadiazole (p-SIDT(FBTTh 2 ) 2 ) as a donor and fullerene derivative ([6,6]-Phenyl-C 71 -butyric acid methyl ester (PC 71 BM)) as an acceptor. By varying SM donor ratios, we observed an enhancement of power conversion efficiency (PCE) from ∼7% to ∼9%. This increase in the PCE can be attributed to the Forster resonance energy transfer (FRET) as confirmed by steady-state photoluminescence measurements.