n‑Type Naphthalene Diimide–Biselenophene Copolymer for All-Polymer Bulk Heterojunction Solar Cells

Abstract

A new solution processable n-type polymer semiconductor is synthesized and characterized for use as an electron acceptor material in all-polymer bulk heterojunction solar cells. The new crystalline copolymer, poly­(naphthalene diimide-<i>alt</i>-biselenophene) (PNDIBS), has a high field-effect electron mobility (0.07 cm²/(V s)) and broad visible-near-infrared absorption band with an optical band gap of 1.4 eV. All-polymer bulk heterojunction solar cells comprised of PNDIBS acceptor and poly­(3-hexylthiophene) donor have a photovoltaic power conversion efficiency of 0.9%. The external quantum efficiency spectrum of the all-polymer solar cells shows that about 19% of the photocurrent comes from the near-infrared (700–900 nm) light harvesting by the new n-type polymer semiconductor