Poly(3-butylthiophene) Inducing Crystallization of Small Molecule Donor for Enhanced Photovoltaic Performance

Morphological control over the bulk heterojunction (BHJ) microstructure of 7'-(4,4-bis (2-ethylhexyl)-4H-silolo[3,2-b:4,5-b']dithiophene-2,6-diyl)bis(6-fluoro-4-(5'-hexyl-[2,2'-bithiophen]-5-yl)benzo[c][1,2,5](thiadiazole) (p-DTS(EBTTh2)(2)) and [6,6]-phenyl-C-71-butyric acid methyl ester (PC71BM) system was demonstrated by introducing a small amount of poly(3-butylthiophene) (P3BT) into the active layer. The P3BT could serve as a heterogeneous nucleating agent, inducing the crystallization of p-DTS(EBTTh2)(2) to form interconnected nanofibers throughout the whole film. Moreover, the phase separation sizes of the active layer increased after incorporation of P3BT, accompanied by the enhanced surface roughness of the films. Therefore, the power conversion efficiency of the devices increased from 3.4% to 5.0% as the P3BT content reached 10 wt %, due to the enhanced light absorption of the active layer, as well as the higher and more balanced hole and electron mobility.