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

Abstract

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 π–π 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.

On the Understandings of Dielectric Constant and Its Impacts on the Photovoltaic Efficiency in Organic Solar Cells

“…[ 58‐59 ] As an example, Zhang et al . [ 60 ] substituted the cyano group for the hydrogen group in PB3T‐C66 to obtain PB3TCN‐C66, and found that B3T‐C66 and PB3T‐C66:IT‐4F blends exhibited ε r of 2.75 and 2.54 at 1 kHz, respectively. In comparison, the cyano‐group based PB3TCN‐C66 donor and its blends with IT‐4F acceptor exhibited higher values of ε r of 4.31 and 3.60 at the same frequency.…”

Emerging Approaches in Enhancing the Efficiency and Stability in Non‐Fullerene Organic Solar Cells

“…For instance, to increase the χ of the hyper-miscibility system PB3T-C66:IT-4F, Duan and coworkers introduced the cyano group to the donor PB3T-C66, improving the domain purity from 0.62 to 1, and significantly increasing the J SC and FF. [103] Finally, the PCE was increased from 2.3% to 11.2%. [103] From the perspective of the acceptor, Hou and coworkers changed the end group of BTP-4Cl to reduce its miscibility with P3HT.…”

“…[103] Finally, the PCE was increased from 2.3% to 11.2%. [103] From the perspective of the acceptor, Hou and coworkers changed the end group of BTP-4Cl to reduce its miscibility with P3HT. [104] The enhanced χ of the system drives an appropriate phase separation, increasing the J SC and FF significantly.…”

Tetrabromination versus Tetrachlorination: A Molecular Terminal Engineering of Nonfluorinated Acceptors to Control Aggregation for Highly Efficient Polymer Solar Cells with Increased Voc and Higher Jsc Simultaneously

“…Polymer solar cells (PSCs) have achieved a huge breakthrough in the past 5 years with the combinational contributions from the developments of nonfullerene acceptors (NFAs), polymeric donors, and kind of redundant of device engineering. [ 1–12 ] Compared with traditional fullerene acceptors, A–D–A framework nonfullerene small molecular acceptors (NF‐SMAs) have significant advantages in broader absorption range, tunable molecular structure and energy levels, and diversified donor materials for matching. [ 13–23 ] Therefore, many such typed NF‐SMAs have been synthesized and become the mainstream materials for the development of high‐efficiency PSCs.…”