The impact of thermal treatment on the performance of benzo[1,2-b:4,5-b′]difuran-based organic solar cells

Abstract

The new low bandgap benzo[1,2-b:4,5-b′]difuran (BDF)-based organic small molecule, namely B1, was synthesized by Stille coupling polymerization reactions. B1 was found to be soluble in common organic solvents such as chloroform, toluene and chlorobenzene with excellent film forming properties. The structure of B1 was verified by ¹H NMR, GC-MS and elemental analysis. The B1 films exhibit broad absorption bands from 300 to 750 nm. The hole mobility of B1 : PC₆₁BM (1 : 1, w/w) blend film reached up to 7.7 × 10⁻² cm V⁻¹ s⁻¹ after thermal annealing by the space-charge-limited current method. BHJ organic solar cells (OSCs) were fabricated with a device structure of ITO/PEDOT : PSS/B1 : C₆₁BM/LiF/Al. When the active layer was thermally annealed at 120 °C, B1 showed the best photovoltaic performance, with a PCE up to 5.0%. We also studied the connection between the morphologies of the active layers and the photovoltaic performance by AFM, PL, etc. Our observation will guide future design for even better small molecules for highly efficient OSCs.