Fully Conjugated Donor–Acceptor Block Copolymers\nfor Organic Photovoltaics via Heck–Mizoroki Coupling

Abstract

The development of facile routes\nto prepare fully conjugated block\ncopolymers (BCPs) from diverse monomers is an important goal for advancing\nrobust bulk-heterojunction (BHJ) organic photovoltaics (OPVs). Herein\nwe introduce a synthetic strategy for step-growth BCPs employing 1,2-bis­(trialkylstannyl)­ethene\nas one monomer, which, in addition to offering improved backbone planarity,\ndirectly yields a vinylene-terminated macromonomer suitable for Heck–Mizoroki\ncoupling. The benefits of our strategy, which facilitates the preparation\nof functionalized macromonomers suitable for BCP synthesis, are demonstrated\nwith a representative BCP based on a diketopyrrolopyrrole (DPP) copolymer\ncoded pBDTTDPP as the donor block and a perylenediimide (PDI) copolymer\ncoded as pPDIV as the acceptor block. Feed ratio optimization affords\ncontrol over the macromonomer chain-end functionalities and allows\nfor the selective formation of a tri-BCP consisting of pPDIV-<i>b</i>-pBDTTDPP-<i>b</i>-pPDIV, which is employed in\na single-component BHJ OPV. Devices achieved a power conversion efficiency\nof 1.51% after thermal stress at 150 °C compared to 0.02% for\na control device consisting of a comparable blend of pBDTTDPP and\npPDIV. The difference in performance is ascribed to the morphological\nstability of the BHJ when using the BCP.