Effect of Crystallizable Solvent on Phase Separation and Charge Transport in Polymer-fullerene Films

The effect of 1,3,5-trichlorobenzene (TCB) as crystallizable solvent on poly[N-9'-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PCDTBT) and [6,6]-phenyl C₇₁ butyric acid methyl ester (PC₇₁BM) bulk heterojunction (BHJ) was investigated. We found that phase separation of PCDTBT and PC₇₁BM and formation of the condensed network of polymers were appropriately regulated by addition of TCB in the BHJ films, which were confirmed by optical microscopic, AFM, and TEM observations in addition to current-voltage analyses. Through the formation of a good continuous pathway for carrier transport by the addition of TCB, 2.5 times enhancement of the hole mobility in the BHJ film was attained from 5.82 × 10⁻⁵ cm² V⁻¹ s⁻¹ without TCB to 1.48 × 10⁻⁴ cm² V⁻¹ s⁻¹ with 20 mg ml⁻¹ of TCB.