Facile Enhancement of Open-Circuit Voltage in P3HT Analogues via Incorporation of Hexyl Thiophene-3-carboxylate

Two families of copolymers featuring varying percentages of hexyl thiophene-3-carboxylate, herein referred to as 3-hexylesterthiophene (3HET), were synthesized via Stille polymerization to generate a series of random poly(3-hexylthiophene-co-3-hexylesterthiophene) (P3HT-co-3HET) copolymers as well as a series of semi-random poly(3-hexylthiophene—thiophene—3-hexylesterthiophene–diketopyrrolopyrrole) (P3HTT-DPP-HET) copolymers. Through the introduction of the strongly withdrawing 3HET component, HOMO energy levels can be tuned, and the open-circuit voltage of the resulting polymer solar cells can be significantly enhanced compared to their parent structures, regioregular P3HT and semi-random P3HTT-DPP. We demonstrate that 50% HET content in random copolymers (P3HT50-co-3HET50) outperforms reference P3HT solar cells. In addition to solar cell performance, the influence of 3HET content on copolymers is evaluated by UV–vis absorption, electrochemical HOMO determination, GIXRD crystallinity measurements, DSC, and SCLC hole mobilities. Favorable properties of the parent structures are preserved, including semicrystallinity, high hole mobilities, and absorption coefficients as well as reproducibly good yields and molecular weights. Copolymers featuring 3HET content showed comparable short-circuit currents with parent copolymers up to 50% 3HET loading and further demonstrate the ability to tune electronic properties with the incorporation of strategic components in semi-random and random copolymers.