High Performance All Polymer Solar Cells by Synergistic Effects of Fine Tuned Crystallinity and Solvent Annealing.
Growing interests have been devoted to the design of polymer acceptors as potential replacement for fullerene derivatives for high performance all polymer solar cells (all PSCs) One key factor that is limiting the efficiency of all PSCs is the low fill factor (FF) (normally <0.65) which is strongly correlated with the mobility and film morphology of polymer:polymer blends. In this work, we find a facile method to modulate the crystallinity of the well known naphthalene diimide (NDI) based polymer N2200, by replacing a certain amount of bithiophene (2T) units in the N2200 backbone by single thiophene (T) units and synthesizing a series of random polymers PNDI Tx, where x is the percentage of the single T. The acceptor PNDI T10 is properly miscible with the low band gap donor polymer PTB7 Th, and the nanostructured blend promotes efficient exciton dissociation and charge transport. Solvent annealing (SA) enables higher hole and electron mobilities, and further suppresses the bimolecular recombination. As expected, the PTB7 Th:PNDI T10 solar cells attain a high PCE of 7.6% which is a 2 fold increase compared to that of PTB7 Th:N2200 solar cells. The FF of 0.71 reaches the highest value among all PSCs to date. Our work demonstrates a rational design for fine tuned crystallinity of polymer acceptors, and reveals the high potential of all PSCs through structure and morphology engineering of semicrystalline polymer:polymer blends.
Journal of the American Chemical Society