Comparison of conventional and inverted structures in fullerene-free organic solar cells

A n-type small molecule DC-IDT2 F, with 4,4,9,9-tetrakis(4-hexylphenyl)-indaceno[1,2-b:5,6-b]dithiophene as a central building block, furan as π-bridges, and 1,1-dicyanomethylene-3-indanone as end acceptor groups,was synthesized and used as an electron acceptor in solution-processed organic solar cells(OSCs). DC-IDT2 F exhibited good thermal stability, broad and strong absorption in 500–850 nm, a narrow bandgap of 1.54 e V,LUMO of –3.88 eV, HOMO of –5.44 eV and an electron mobility of 6.5 × 10–4cm2/(V·s). DC-IDT2F-based OSCs with conventional and inverted structures exhibited power conversion efficiencies of 2.26 and 3.08%, respectively. The effect of vertical phase separation and morphology of the active layer on the device performance in the two structures was studied.