Highly Efficient Solar Cells Based on the Copolymer of Benzodithiophene and Thienopyrroledione with Solvent Annealing

Highly efficient PBDTTPD-based photovoltaic devices with the configuration of ITO/poly­(3,4-ethylenedioxythiophene)-poly­(styrenesulfonate) (PEDOT:PSS)/PBDTTPD: methanofullerene (6,6)-phenyl-C₆₁-butyric acid methyl ester (PC₆₁BM) (weight ratio being from 1:1 to 1:4)/LiF (5 Å)/Al (100 nm), were realized with ortho-dichlorobenzene (DCB) solvent annealing treatment. It was revealed that the best photovoltaic device was obtained when the blend ratio of PBDTTPD:PC₆₁BM was modulated to be 1:2 and processed with DCB solvent annealing for 12 h. The short-circuit current density (<i>J</i>_sc) and power conversion efficiency (PCE) values were measured to be 10.52 mA/cm² and 4.99% respectively, which were both higher than the counterparts treated with chlorobenzene (CB) solvent annealing or the thermal annealing. Atomic force microscopy measurements of the active layer after solvent annealing treatment were also carried out. The phase separation length scale of the PBDTTPD:PC₆₁BM­(1:2) layer was comparable to the exciton diffusion length when the active layer was treated under DCB solvent annealing, which facilitated effective exciton dissociation and carrier diffusion in the active layer. Therefore, highly efficient PBDTTPD-based photovoltaic devices could be achieved with DCB solvent annealing, which indicated that solvent annealing with proper solvent might be an easily processed, low-cost, and room-temperature alternative to thermal annealing for polymer solar cells