Cost-effective polymer donors based on pyridine for efficient nonfullerene polymer solar cells

Developing cost-effective polymer donors that can match nonfullerene acceptors is very important for practical applications of polymer solar cells (PSCs). In this work, low-cost 3-fluoropyridine and pyridine were employed as acceptor unit cores to construct cost-effective polymers PBDT-FPy, PBDT-Py and PBDF-Py by copolymerizing with commercially available donor units. PBDT-FPy, PBDT-Py and PBDF-Py show wide-bandgap of 2.08, 2.15 and 2.05 eV, respectively. Due to the strong electronegativity of nitrogen atom in pyridine and Nδ− … Hδ+ noncovalent dipole-dipole interactions, all polymers exhibit deep-lying highest-occupied molecular orbital (HOMO) energy levels, strong intermolecular π-π interaction and good planarity. The PBDT-FPy: Y6 based device exhibits a power conversion efficiency (PCE) of 8.34%, while the performance of PBDT-Py: Y6 and PBDF-Py: Y6 devices was significantly improved, with PCE of 10.02% and 10.00%. The results indicate that pyridine with simple structure and low synthetic cost is a promising building block to construct high-performance cost-effective polymer donors for application in PSCs.