Effects Of Vinylene And Side Chain On The Photoelectric Properties Of Benzothiadiazole Conjugated Polymers

Polymer semiconductor materials opened up one of the most hopeful prospects for large-area flexible electronic devices due to their low fabrication cost, lightweight and mechanical flexibility.Except for the electron-rich and electron-deficient units, both the linker effect in the backbone and the substitutional position of the alkyl chains can affect polymer properties. In the project, a series of alternate donor-acceptor conjugated polymers based on benzothiadiazole unit were carried out to study the influence on energy level, molecular structure and field effect property by means of UV, CV, DFT and constructing OFETs devices.The main contents are described as follows:①Designed and synthesized conjugated polymers DA1, DA2 and DA3. The result manifested that introduction of vinylene into DA2, DA3 molecular backbones, affecting the highest occupied molecular orbital(HOMO) mainly, and led to a decreased bandgap. To investigate the carrier transport properties of the polymers, bottom-gate/top-contact OFETs were fabricated by spin-coating and all showed p-type transisitors. Molecule became torsional when the thiophene units connected with σ bond, and mobility of DA1 was 1.4×10-4cm2/(Vs); When the thiophene units connected with vinylene linker, mobility of DA2 reach to 2.1×10-3cm2/(Vs) with planar structure; Mobility of DA3 even obtained up to 0.024 cm2/(Vs), when vinylene linker was introduced between BT units and thiophene units.Polymer film morphologies were investigated using XRD and AFM, all were amorphous either in room temperature or after annealed at 160 oC, while crystallinity improved.②To understand substitutional position of alkyl chains exerted its influence on the device performance of organic semiconductors, we designed and synthesized conjugated polymers DA4, DA5, DA6 based on polymers above. We found the effects of side chain have much influence on the photoelectrical properties of DA4, DA5.The incorporations of vinylene linker didn’t enhance the planarity of DA5, on the contrary, the absorption spectra of DA5 showed remarkable blue-shifted 5nm, 35 nm compared to DA4 in thin solution and film, and the bandgap of DA5 increased to 2.00 e V. We adopted the same way above to construct OFETs, all exhibited p-type transporting performance. As a result, compared with DA1 and DA2, mobility of DA4 and DA5 decreased to 1.2×10-6 cm2/(Vs), 0.7×10-6cm2/(Vs).However, DA6 was up to 0.011 cm2/(Vs), which stayed with DA3 in the same order of magnitude.