Study On Preparation And Optoelectronic Properties Of Phycocyanin-Based Thin Films

Traditional inorganic terahertz(THz) absorbing materials have the disadvantages of limited species, poor selectivity for incident lights, and severe preparation conditions, which limit the development of THz detectors. On the contrary, organic materials exhibit the advantages of high selectivity, low cost, and simple process. Consequently, seeking THz organic materials has become a new route for improving the absorption of THz detectors.As a kind of photosynthetic pigments, phycocyanin(PC) participates the absorption and delivery of light in photosynthesis. So it is possible that valuable information might be deduced from study on PC-based materials, this is why we chose PC as our research object. In this dissertation, we extracted and purified PC as well as phycocyanobilin(PCB). Based on the as-yielded organics, PC–single-walled carbon nanotube(SWCNT) and PCB–SWCNT composite thin films were prepared by spray coating. The resulting films were systematically investigated by metallographic microscope, scanning electron microscope(SEM), Fourier transform infrared(FTIR) spectroscopy, UV-vis spectroscopy, and high resistance meter, respectively. The main results of this thesis are listed below:(1) Terahertz(THz) spectra of PC and PCB thin films were investigated. It was found that both PC and PCB have significant absorption peaks in THz region. By comparison, we deduced that the absorption of PC in THz is mainly caused by its colorant PCB. The characteristic absorption peaks of PC at 81 cm-1 and 48 cm-1 have also been assigned. Combining the simulation of PCB single molecular structure based on DFT, the characteristic absorption peaks of PCB at 60, 70, 96, 123, 214 and 247 cm-1 have been assigned. Moreover, the vibrations of PCB in high wavenumber range of THz are orignated from the vibration of PCB molecular skeleton.(2) PC–SWCNT and PCB–SWCNT composite thin films were further successfully prepared. The THz spectra of these two kinds of films revealed that few influence of the additional SWCNTs on the absorption peaks of PC and PCB in high THz wavenumber range was observed. In addition, the phenmonon of the shifts of the absorption peaks of these composite films at 60 cm-1, 70 cm-1 and 96 cm-1 was explained. This is attributed to the creations of hydrogen bonds by the interactions between the carboxy in carbon nanotubes and methyl in PCB. Such hydrogen bonds cause the change of the vibration pattern, and thus resulting in the shifts of the absorption peaks.(3) PC–SWCNT and PCB–SWCNT composite thin films with different SWCNT concentrations were also prepared and investigated. Results revealed that the sheet resistances of PC–SWCNT and PCB–SWCNT composite films are decreased with the increase of the SWCNT concentration. Resistance-temperature curves of PC–SWCNT composite thin films indicated that PC has bad thermal stability, which denaturation temperature is 45℃. Unlike PC–SWCNT composite films, PCB–SWCNT composite films exhibit better thermal stability and electrical properties. Therefore, the applications of PCB–SWCNT composite films in optical or electronic devices are more promising. Importantly, with systematic investigations on the morphologies, optical and electrical properties of the composite films with different SWCNT concentrations, the optimal concentration of SWCNT in PCB–SWCNT composite thin films was deduced to be ?7%.