Highly Efficient Solar
Cells Based on the Copolymer
of Benzodithiophene and Thienopyrroledione with Solvent Annealing
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Abstract
Highly efficient PBDTTPD-based photovoltaic devices with
the configuration
of ITO/poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS)/PBDTTPD:
methanofullerene (6,6)-phenyl-C<sub>61</sub>-butyric acid methyl ester
(PC<sub>61</sub>BM) (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:PC<sub>61</sub>BM was modulated to
be 1:2 and processed with DCB solvent annealing for 12 h. The short-circuit
current density (<i>J</i><sub>sc</sub>) and power conversion
efficiency (PCE) values were measured to be 10.52 mA/cm<sup>2</sup> 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:PC<sub>61</sub>BM(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