Tailoring π-conjugated dithienosilole–benzothiadiazole oligomers for organic solar cells

Abstract

A series of donor–acceptor type of π-conjugated oligomers based on dithieno[3,2-b;2′,3′-d]silole as the electron donor and 2,1,3-benzothiadiazole as the electron acceptor were designed and synthesized. It was found that the elongation of the molecular lengths of the chromophores can significantly influence the thermal properties, UV-vis absorption, electrochemical properties, and photovoltaic performances of fabricated organic solar cells. The higher molecular weight chromophore exhibited a narrower band gap compared to lower molecular weight counterparts. Solution processed bulk-heterojunction organic solar cells were fabricated with the inverted device structure of ITO/PFN-OX/oligomer:PCBM/MoO₃/Al, in which the best device performance was achieved with a power conversion efficiency of 1.12%. These results indicated that the elongation of the molecular length of π-conjugated small-molecules can be an effective strategy for improving the organic photovoltaic performance of narrow band-gap chromophores.