Design and Synthesis of Wide-bandgap Conjugated Polymers Based on 3,4-Dicyanothiophene for Efficient Organic Solar Cells

In this contribution, we report a set of wide bandgap conjugated polymers (PB3TCN-C32, PB3TCN-C36, PB3TCN-C36-R, PB3TCN-C40) based on 3,4-dicyanothiophene (DCT) for use as electron donors in organic solar cells (OSCs). The polymers exhibit wide optical bandgaps (> 1.8 eV) and deep highest occupied molecular orbital (HOMO) levels due to the high electron affinity of DCT unit. The optoelectronic properties, active layer morphology, and device performance of the polymers can be tuned by side chains. As a result, high-performance solar cells with a decent power conversion efficiency (PCE) of 11.2% have been achieved by PB3TCN-C40 when using IT-4F as the electron acceptor. Noticeably, the polymers afforded a high open circuit voltage (V-oc) of up to 0.92 V and an energy loss (E-loss) as low as 0.6 eV even though there is not any additional withdrawing groups such as F, Cl, or S atom on the polymers, which is superior to the leading polymer donors in the field of OSCs. These results suggest that the DCT unit hold big room for further increasing V-oc and decreasing E-loss of OSCs via rational polymer design, which is desirable for application in tandem devices and in-door photovoltaics. Overall, this work demonstrated that DCT is a promising building block for constructing wide bandgap conjugated polymer with deep HOMO level for highly efficient OSCs.