Synthesis and characterization of a thienopyrazine-based low band-gap poly(arylene ethynylene) and photocell studies of the poly-yne/perylene dye blend with broad photocurrent spectrum

Background: In the quest for sustainable energy materials, new donor and acceptor materials are being designed, synthesized and tested for photovoltaic (PV) applications. In this context, conjugated organic polymers have received significant interests in the last few decades. Objective: In the present work, we synthesized an organic poly-yne P and assessed its efficiency as donor with a rylene acceptor EP-PTC. Methods: The organic poly-yne P was synthesised via Sonogashira coupling and characterized by analytical and spectroscopic techniques. The PV performance of blends composed of different amounts of polymer P and acceptor EP-PTC was assessed. Computational studies were undertaken at DFT level to determine the geometry, dipole moment, Mulliken charge and energy level. Results: A soluble blue low band-gap (1.72 eV) π-conjugated co-polymer consisting of dioctyloxyphenylene unit linked via ethynylene to 2,3-diphenylthieno[3,4-b]pyrazine has been synthesized and characterized. Blends of P and a soluble organic dye EP-PTC showed good PV performance with broad photocurrent spectra. The copoly-yne/dye-based solar cell with high EP-PTC content shows significantly higher external quantum efficiency (EQE) compared to the single material-based devices. However, a decrease in EQE was observed upon thermal annealing. DFT calculations showed convergence of the experimental results. Conclusion: We have synthesized and characterized a thienopyrazine-based organic co-polyyne and showed that blends of co-polymer P and the perylene dye EP-PTC possess high EQE up to 5.5% for the 90: 10 EPPTC: P blend at wavelengths between 350 nm and 710 nm.