3,4-Dicyanothiophene-a Versatile Building Block for Efficient Nonfullerene Polymer Solar Cells

In this contribution, a versatile building block, 3,4-dicyanothiophene (DCT), which possesses structural simplicity and synthetic accessibility for constructing high-performance, low-cost, wide-bandgap conjugated polymers for use as donors in polymer solar cells (PSCs), is reported. A prototype polymer, PB3TCN-C66, and its cyano-free analogue polymer PB3T-C66, are synthesized to evaluate the potential of using DCT in nonfullerene PSCs. A stronger aggregation property in solution, higher thermal transition temperatures with higher enthalpies, a larger dipole moment, higher relative dielectric constant, and more linear conformation are exhibited by PB3TCN-C66. Solar cells employing IT-4F as the electron acceptor offer power conversion efficiencies (PCEs) of 11.2% and 2.3% for PB3TCN-C66 and PB3T-C66, respectively. Morphological characterizations reveal that the PB3TCN-C66:IT-4F blend exhibits better pi-pi paracrystallinity, a contracted domain size, and higher phase purity, consistent with its higher molecular interaction parameter, derived from thermodynamic calculations. Moreover, PB3TCN-C66 offers a higher open-circuit voltage and reduced energy loss than most state-of-the-art wide-bandgap polymers, without the need of additional electron-withdrawing substituents. Two additional polymers derived from DCT also demonstrate promising performance with a higher PCE of 13.4% being achieved. Thus, DCT represents a versatile and promising building block for constructing high-performance, low-cost, conjugated polymers for application in PSCs.