Revisiting the Dithienophthalimide Building Block: Improved Synthetic Method Yielding New High-Performance Polymer Donors for Organic Solar Cells.

Imide-functionalized arenes have been one of the most promising acceptor (A) units in organic solar cells (OSCs). However, dithienophthalimide (DPI), a hybrid of thieno-[3,4-c]pyrrole-4,6-dione (TPD) and bithiophene imide (BTI) units, has not been revisited since its first synthesis, likely owing to the high synthetic cost of the reported method. In this work, we simplified the synthetic procedure of the DPI skeleton with a significant reduction of the synthetic cost by using chromium-mediated cyclization as the key chemistry. Using this method, two DPI-based nonhalogenated D-A copolymers are synthesized. The binary OSCs based on pBDTT-DPI-Me : Y6 achieves a power conversion efficiency as high as 16.55 %, highlighting DPI as an attractive A-unit for further exploration in OSCs.