Z-scan Study on Nonlinearity of Thermally Annealed Zinc Phthalocyanine

• Main Authors: Chuang, Yen-Chen, 莊彥晨
• Other Authors: Ahn, Hyeyoung
• Format: Others
• Language: en_US
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/72253792528290420644

碩士 === 國立交通大學 === 光電工程研究所 === 105 === Due to their superior properties including ultrafast response, thermal and chemical stability, and flexible processing, metallophthalocyanines (MPcs) are one of the most extensively studied materials for optoelectronic devices, such as thin film transistors. Its high optical linearity also makes it a potential candidates for all-optical-switching. Among MPcs, zinc Pc (ZnPc) is an interesting material for photovoltaic and photoconductivity applications due to its high absorption coefficient, high energy conversion efficiency, and photochemical stability. In our previous study, we found that thermal annealing at ~200 °C could induce phase transition from metastable α-phase to stable β-phase polymorph in ZnPc. In particular, the carrier dynamics of ZnPc near the absorption edge is closely related to the subabsorption band of polymorph. Despite of great interest, optical nonlinear properties of α- and β-phase ZnPc near the absorption has not been studied yet, and in this thesis, we present the nonlinear absorption and nonlinear refraction properties of ZnPc studied by the absorption spectroscopy and Z-scan technique. We found that the band-filling effect dominates the linear and nonlinear absorption processes of ZnPc samples. Although the phase transition is not complete at annealing temperature of 150 °C, the nonlinear property of 50 nm-thick ZnPc shows a clear evidence of phase transition. Organic materials have high optical absorption, but relax slowly so that accumulated energy due to high repetition rate (80 MHz) of our laser system causes a serious thermal heating and thermal lens effect. After series of effort to reduce the thermal heating problem, we could measure the nonlinear refraction coefficient of ZnPc sample annealed at 150 °C.