Amorphous Polymer Acceptor Containing B ← N Units Matches Various Polymer Donors for All-Polymer Solar Cells

Polymer acceptors for high-efficiency all-polymer solar cells (all-PSCs) are generally semicrystalline. In this manuscript, we report an amorphous polymer acceptor, which matches well with a variety of polymer donors to produce efficient all-PSCs. The amorphous polymer acceptor (rr-PBN) is a regiorandom polymer consisting of alternating asymmetric B←N bridged thienylthiazole (BNTT) unit and pyridine-flanked diketopyrrolopyrrole (PyDPP) unit. It is amorphous in thin film because of its regiorandom structure and the large steric hindrance. rr-PBN shows deep LUMO/HOMO energy levels of -3.71/-5.81 eV, strong sunlight harvesting capability and high electron mobility of 2.20 × 10^-4 cm² V^-1 s^-1. As a polymer acceptor, rr-PBN matches well with three commercially available polymer donors, J71, PTB7-Th, and PffBT4T-2OD to give excellent percolating bicontinuous network morphology in all-PSCs. We propose that the crystallization of polymer donors governs the film-forming process and dominates the phase separation morphology, leading to good phase separation morphology. The all-PSC devices all show power conversion efficiencies (PCEs) of 5.2-6.6%. This study provides a new direction to design polymer acceptors and a novel approach to control phase separation morphology of all-PSCs.