Sustainable conjugated polymer synthesis in OPV: a case study from conventional to flow and microwave-assisted synthesis

Organic photovoltaics (OPVs) emerge as a promising alternative to silicon-based solar cells, especially for indoor applications, due to their lightweight, flexibility, and potential for low-cost production. A key challenge remains the development of scalable and environmentally friendly methods for synthesizing conjugated polymers, essential components of the active layers in OPV devices. To increase their economic viability and their sustainability, it is essential to combine low-cost, large-scale module production with greener conjugated polymer production and minimal batch-to-batch variation.

Continuous flow and microwave-assisted syntheses represent two efficient, sustainable approaches aligned with green chemistry principles. Continuous flow significantly reduces reaction times and solvent use, while microwave-assisted methods further enhance sustainability by minimizing solvent consumption and energy input, and enabling faster reactions. These advanced methods can thus play a crucial role in developing next-generation OPV materials in a more cost-effective and environmentally responsible way.

Here we present the case study of PSBTBT (poly(4,4-dioctyldithieno(3,2-b:2',3'-d)silole)-2,6-diyl-alt-(2,1,3-benzothiadiazole)-4,7-diyl), a low band gap electron-donating polymer for OPVs. We have developed the PSBTBT Stille cross-coupling polymerization using different approaches: conventional, continuous flow and microwave-assisted methods. To assess the impact of the different synthetic methods, we performed molecular and spectroscopic characterization to highlight correlations between the synthesis technique and the resulting material properties.