π‐Extended End Groups Enable High‐Performance All‐Polymer Solar Cells with Near‐Infrared Absorption

Abstract

Comprehensive SummaryNarrow‐bandgap n‐type polymers are essential for advancing the development of all‐polymer solar cells (all‐PSCs). Herein, we developed a novel polymer acceptor PNT with π‐extended 2‐(3‐oxo‐2,3‐dihydro‐1H‐cyclopenta[b]naphthalen‐1‐ylidene) malononitrile (CPNM) end groups. Compared to commonly used 2‐(3‐oxo‐2,3‐dihydro‐1H‐cyclopenta[b]naphthalen‐1ylidene) malononitrile (IC) units, CPNM units have a further extended fused ring, providing the PNT polymer with extended absorption into the near‐IR region (903 nm) and exhibiting a narrow optical bandgap (1.37 eV). Furthermore, PNT exhibits a high electron mobility (6.79 × 10−4 cm2 V−1 S−1) and a relatively high‐lying lowest unoccupied molecular orbital (LUMO) energy level of −3.80 eV. When blended with PBDB‐T, all‐PSC achieves a power conversion efficiency (PCE) of 13.7% and a high short‐circuit current density (JSC) of 24.4 mA cm−2, mainly attributed to broad absorption (600‐900 nm) and efficient charge separation and collection. Our study provides a promising polymer acceptor for all‐PSCs and demonstrates that π‐extended CPNM units are important to achieve high‐performance for all‐PSCs.This article is protected by copyright. All rights reserved.