Synthesis And Properties Of Solution-Processable Organic Small-Molecule Photovoltaic Materials With D-A-D-A-D Extended Structure

Organic solar cells currently have become a hot research topic in the field of photoelectric. As a new technology, solution-processable BHJ-OSCs have lower conversion efficiency than inorganic solar cells, but it has many advantages, such as more varieties, light-weight, low-cost, good flexibility, simple wortmanship and so on.The study of solution-Processable organic small-molecule photovoltaic material mainly concentrates on the structure of D-A-D and A-D-A. In order to explore the research train of thought, this paper designed and synthesized small molecule organic photovoltaic materials with the structure of D-A-D-A-D. We expect a better effect of photoelectric conversion efficiency with a longer conjugated structure, which can achieve a narrower band gap, and more structures of D-A (A-D), which can result in stronger intramolecular charge transfer.This paper adopts 3,6-carbazole as the middle electron-donating (D) unit, triphenylamine as side electron-donating (D) unit and benzotriazole(BTA), benzothiadiazole(BT) with alkyl chain as electron-withdrawing (A) unit and single bond, double bond, double bond with cyano and triple bond as bridge bond to synthesize two series small molecule photovoltaic materials. Density functional theory calculations, UV-visible absorption test and the cyclic voltammorgrams indicate that the molecules have stronger optical absorptivity and appropriate energy level, which indicate that all of this molecules are better BHJ-OSCs photovoltaic materials. Therefore,we manufacture the devices and test. Photoelectric data indicate that compared with BTA series, molecules based on BT with alkyl chain as electron-withdrawing (A) unit have higher photoelectric conversion efficiency (3.39%-3.99%) and higher short circuit current density (11.6mAcm-2). At the same time, this paper also research the influence of the brige bond, acceptor unit and extended strucuture for the photovoltaic performance. It demonstrates that:molecules with single bond have better photovoltaic performance and molecules with electron-withdrawingunit of double bond with cyano and triple bond can adjust the HOMO level and Voc; BT series have narrower bandgap,which results in a higher Jsc; the extended D-A-D-A-D molecule have narrower bandgap and higher charge carrier mobility comparing with the molecues of A-D-A of BTA series it also have higher Jsc, FF and PCE.The research achievements of the paper will provide a new train of thought for the design of molecules with longer structure.