Synthesis and Photovoltaic Performance of Anthracene-Based Small Molecules for Solution-Processed Organic Solar Cells

Increasing molecular π-conjugation length generally improves the light-harvesting ability and enhancing π-π stacking interactions could improve the charge-carrier transport ability in small molecules (SMs). Both are beneficial for increasing power conversion efficiencies (PCEs) in organic solar cells. In this work, two linear (A−D)₂Ar-type SMs of (DTBT-TPA)₂An and (DPP-TPA)₂An were designed and synthesized, in which 4,7-di(thiophen-2-yl)benzothiadiazole (DTBT) and diketopyrrolopyrrole (DPP) were selected as electron acceptors (A), triphenylamine (TPA) was used as electron donor (D) and 9,10-anthracene (An) was used as π-bridge (Ar group), respectively. For comparison, two D−A-type SMs of DTBT-TPA and DPP-TPA were also prepared without anthracene unit. By systematically comparing their optical and electronic properties, it was found that (A−D)₂Ar-type SMs show stronger photo response with higher absorption coefficients than the D−A-type counterparts. And introducing anthracene unit could slightly lower their HOMOs of the resulting (A−D)₂Ar-type SMs. In bulk heterojunction solar cells, PCEs of 1.72% and 1.36% were achieved in (DTBT-TPA)₂An and (DPP-TPA)₂An based devices without any solvent additive, which are about 1.5 and 1.9 times the corresponding values of the DTBT-TPA and DPP-TPA based devices, respectively.