Conjugated polymers have received tremendous attentions for the past decades because they show promising applications in low-cost, large-area and flexible electronic devices. Many studies manifest that apart from conjugated backbones, the side chains can dictate the self-organization of the polymer owing to the fact that side chains tend to form low-energy and space-filling structures.

Research group led by Prof. ZHANG Deqing at the Institute of Chemistry of Chinese Academy of Sciences (ICCAS) has made progress in the side-chain engineering. They report the remarkable enhancement of the semiconducting properties for DPP-quaterthiophene conjugated polymers by incorporating hydrogen-bonding containing urea groups in the alkyl side chains. This work was published on J. Am. Chem. Soc.

AFM, GIXRD, and STEM results suggest that the presence of urea groups facilitates the assemblies of conjugated polymers into nanofibers and ordered aggregation of PC₇₁BM. Therefore, the hole mobility of thin film of polymer containing urea groups reaches 13.1 cm² V^-1 s^-1 after thermal annealing at just 100 ^oC. The incorporation of urea groups in the side alkyl chains also has an interesting effect on the photovoltaic performances of DPP-quaterthiophene conjugated polymers after blending with PC₇₁BM. The power conversion efficiency (PCE) reach 6.8% for blend thin films based on polymer containing urea groups and PC₇₁BM. These results demonstrate that side chain engineering via hydrogen-bonding (through the incorporation of urea groups) is a powerful strategy to improve the charge carrier mobilities and photovoltaic performance for conjugated polymers.

This work is financially supported by the Strategic Priority Research Program of the Chinese Academy of Sciences and the National Natural Science Foundation of China.

Chemical structure of urea-containing polymers (Image by ZHANG Deqing)

Contact:

Prof. ZHANG Deqing

CAS Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences

Email: dqzhang@iccas.ac.cn