Solvent Annealing Effects in Dithieno[3,2-b:2′,3′-d]pyrrole–5,6-Difluorobenzo[c][1,2,5]thiadiazole Small Molecule Donors for Bulk-Heterojunction Solar Cells

Abstract

Low-bandgap small molecule (SM) donors that can be solution-processed with fullerene acceptors (e.g., PC61/71BM) are proving to be particularly promising in bulk-heterojunction (BHJ) solar cells. Compared to their π-conjugated polymer counterparts, SM donors are well-defined (monodisperse) and more synthetically modular, with relatively wide ranges of bandgaps that can be achieved in stepwise couplings of various donor and acceptor motifs. However, the optimization of SM–fullerene morphologies and BHJ device efficiencies relies more specifically on the use of processing additives, postprocessing thermal, or solvent vapor annealing (SVA) approaches, and achieving adequate interpenetrating networks and structural order in BHJ thin films can be challenging. In this report, we examine the correlated effects of molecular structure and postprocessing SVA on the BHJ solar cell performance of a set of π-extended SM donors composed of dithieno[3,2-b:2′,3′-d]pyrrole (DTP) and 5,6-difluorobenzo[c][1,2,5]thiadiazole ...