Structurally Pure and Reproducible Polymer Materials for High-Performance Organic Solar Cells

The commercial uptake of (polymer-based) organic solar cells is among others hindered by poor reproducibility of the device performance, arising from the variability in molar mass distribution and the presence of structural defects in push-pull conjugated polymers. Traditional "in-flask" synthesis methods and commonly used catalysts contribute to these issues. Flow chemistry has been proposed to provide consistent molar masses, while a recently applied Buchwald catalyst shows promise for reduced structural defect formation. However, this catalyst has not been used for donor polymers affording state-of-the-art efficiencies in organic solar cells, such as PM6 and D18. In this work, we utilize these two polymers as model systems to probe the effect of different synthetic conditions and examine the precise chemical structures, including any homocoupled defects present, by matrix-assisted laser desorption/ionization time-of-flight (MALDI-ToF) mass spectrometry. Additionally, we analyze how these structural factors impact the material and device properties. By combining droplet-flow chemistry and defect-free synthesis, we demonstrate a reproducible and scalable protocol for the synthesis of donor polymers with a tailorable molar mass for high-efficiency organic photovoltaics.