Preparation Of Graphene Oxide Functionazed With Amino Acid And Study Its Photoelectric Property

Graphene oxide?GO? is a common derivative of graphene. It disperses well in water/alcohol solvents due to its significant amounts of oxygen-carrying groups such as carboxyl, hydroxyl, and epoxy. Graphene or GO is a promising next generation candidates for the transparent conducting electrode of optoelectronic devices. In order to obtain significantly high device performance, it is extremely important to match the work function of an electrode to the energy levels of an active layer in devices for the efficient transfer of hole or electron between the electrode and the active layer. However, the work function of graphene?4.7 e V? and GO?5.3 e V? does not match well with the molecular energy levels of most active materials. Therefore, controlling the work functions of graphene or GO is essential for its applications in photoelectric devices. In previous reports, amino acids, as a type of dipole, haved been applied in modifying the surface work function of indium tin oxides?ITO? due to the the effect of surface dipole. Better performance of photoelectric devices has been obtained. In this study, GO sheets functionalized with amino acids were fabricated via a mild and environmentally friendly approach, aiming at changing the work function of GO. The main work is as follows:GO was prepared by the modified Hummers method. Then the as-prepared GO was reacted with sodium chloroacetate, which resulted in the conversion of the hydroxyl groups on the edge of the original GO into carboxyl groups. Carboxylated GO was activated by Thionyl chloride?SOCl₂? at 65°C for 24 h, and the product is denoted as GOCl. Subsequently, GOCl is reacted with amino acids in a solution of N, N-Dimethylformamide?DMF? at 90°C for 24 h. The so-obtained samples were Graphene oxides functionalized by amino acid?GO-AA?. GO and GO-AA were characterized by a series of characterization Methods. The results indicated that amino acids were covalently grafted to the GO by forming amide bonds. The work function of GO was 5.3 e V. The work function of GO-AA could be controlled over a wide range from 4.0 to 4.5 e V. The work function of original graphene measured in the study was about 4.7 e V.Further, the as-prepared graphene compounds were composited with poly?3, 4-ethylenedioxythiophene?: poly?styrenesulfonate??PEDOT:PSS?. The work function of compounds decreases to less than 4.5 e V. Thin film about 20 nm in thickness was obtained by spinning-coating the above compounds suspension. The films have high UV-Visible transmittance of above 85% and high conductivity of 1749 S·cm-1.Organic solar cells fabricated with the cathodes containing GO-AA, which has higher short-circuit current density?JSC??open circuit voltage?VOC??photoelectric conversion efficiency?PCE? and external quantum efficiency?EQE? compared to the blank one at the same process conditions. Especially, organic photodetectors fabricated with the cathodes containing ITO/PEDOT:PSS + GO-Cys?graphene oxide functionalized by cysteine? have a highest D* of 5.7 × 10¹² Jones at-0.1 V complying with a fast response speed. The results in this work imply that these functionalized GO have a promising potential to act as transparent electrode materials in the application of organic, inorganic, and hybrid electronic devices.