Use thiophene as a comonomer alternative to triphenylamine combine with 4, 8-dithienylbenzo [1,2-b: 4, 5-b'] dithiophene as a polymer dye in sensitized solar cells

• Synthesized two new 4, 8-dithienylbenzo dithiophene based polymers.
• The two polymers were successfully used as dyes for DSSCs.
• The polymer based on triphenylamine has higher absorption ability and IPCE peak.
• The simplified polymer (PPTB8) has higher Jsc and power conversion efficiency.

Triphenylamine (TPA) and its derivatives are well-known pigments with excellent electron donating abilities and chemical, thermal and photochemical stabilities, and have been used in various optical and electronic fields. In this context, the polymer PPAB7 containing a TPA and a 4, 8-dithienylbenzo [1,2-b: 4, 5-b'] dithiophene (BDT) as the donor group in the main chain and a cyanoacetic acid accepter in the side chain, linked by a thiophene unit is synthesized. To study the influence of donor in the backbone, we crop out the TPA and use the linker thiophene unit as a comonomer directly then a new polymer PPTB8 is synthesized. Combining a mesoporous titania film grafted by these two simple polymer dye with I−/I3− redox couple, the none TPA sensitizer PPTB8 based DSSC obtained higher power conversion efficiency (PCE) of 3.78% than PPAB7 of 2.21% with a degree of polymerization (DP) of ∼5 and ∼6, respectively, at an irradiance of the AM 1.5 G sunlight. To understand the improvement performance of PPTB8, theoretical calculations, absorption-emission spectra, electrochemistry, infrared spectroscopy and photovoltaic measurements are used to compare the photophysics, interfacial and photovoltaic property of the two polymers. The results suggest that the increased photovoltaic property of the simplified structure (PPTB8) is due to its broader spectra and higher efficient electron injection property resulting in higher short current.