Synthesis And Properties Of Organic Photovoltaic Materials Based On Quinoxaline

Photovoltaic small molecules have attracted extensive attention due to their special advantages of well-defined structures, easier purification and better batch-to-batch reproducibility. To obtain efficient devices, they should simultaneously have strong absorption ability, suitable HOMO-LUMO energy levels, high charge carrier mobility, and good film-forming properties. Quinoxaline (Qx) is one of most common building blocks to construct photovoltaic compounds meeting the above requirements when it is used as an electron-accepting (A) unit to combine with electron-donating (D) moieties. Therefore, in this article, a series of D-A-D type organic small molecular photovoltaic materials for organic solar cells have been designed, which contain Qx as acceptor and triphenylamine (TPA) as donor. To improve the molecular solubility, aliphatic side-chains and alkoxy-chains were introduced. In addition, cyano was introduced on the conjugated bridge bonds.The structure of the as-synthesized compounds were proved and confirmed by 1H-NMR. The photophysical, electrochemical and photovoltaic properties of the molecules have been extensively studied by the density functional theory (DFT) calculations, UV-vis absorption spectroscopy and cyclic voltammetry. The solution-processable organic solar cells with synthesized molecules as donor and PC61BM as acceptor were fabricated and measured. (1) The lower HOMO of alkoxy-Qx series materials could effective increase the open-circuit voltage (Voc). (2) The solubility and planarity was affected by the introduction of aliphatic side-chains and alkoxy-chains. (3) Both cyano vinyl and carbon-carbon triple bond as π-bridge could lower the HOMO and obtain high Voc. (4) Among the all donor materials, TPACNTQx showed a impressive PCE of 6.25% with a Voc of 0.95 V, a Jsc of 14.08 mA·cm-2, and a fill factor (FF) of 47%. To date, the remarkable PCE of TPACNTQx is the highest efficience for solution-processed organic small molecules (OSMs) based on Qx and TPA.The results of photovoltaic performances of organic solar cells (OSCs) based on these materials show that the molecular design is crucial to achieve organic small molecular photovoltaic materials with good stability and a high photovoltaic efficiency. The dissertation discussed how TPA affect photovoltaic properties, compared the effect of different π-linkage, analyzed results of aliphatic side-chains and alkoxy-chains on molecular planarity and solubility, and evaluated influence of cyano acting on energy levels. This attractive result was of great value to the design of organic small molecular photovoltaic materials based on Qx and TPA.