Fully conjugated block copolymers for single-component solar cells: synthesis, purification, and characterization

Abstract

Fully conjugated donor–acceptor (D–A) block copolymers, P3HT-b-PBIT2, containing p-type poly(3-hexylthiophene) and n-type poly(pyrene bisimide) segments are synthesized in a one-pot reaction via Stille coupling polycondensation. Various D–A block copolymers with low polydispersities (1.17–1.54) are obtained through further separation by preparative GPC. The structural and molecular features of block copolymers are verified by ¹H NMR, Fourier transform infrared spectroscopy (FTIR), UV-Vis absorption, and cyclic voltammetry (CV). It is found that optical and electrochemical properties of D–A block copolymers are strongly dependent on the combination ratio of the donor P3HT and acceptor PBIT2 segments. When the PBIT2 weight content increases, the absorption intensity of PBIT2 in D–A block copolymer fractions is enhanced simultaneously. The highest occupied molecular orbital (HOMO) levels of the block copolymers increase gradually with decreasing acceptor block lengths and are located between P3HT and PBIT2. All-polymer solar cells using the preparative GPC separated P3HT-b-PBIT2 (BCP1-1) as a single-component active layer, which shows mono-modal GPC curves and a comparatively balanced hole and electron mobility of 2.36 × 10⁻⁴ and 1.15 × 10⁻⁵ cm² V⁻¹ s⁻¹, respectively, achieve a power conversion efficiency of 1.0% with an open-circuit voltage of 0.43 V, a short-current of 5.29 mA cm⁻², and a fill factor of 0.43.