| Small organic molecules play an important role in the organic semiconductor devices. Organic semiconductor devices are portable, highly efficient, inexpensive, and environmental friendly, and can be broadly used for lighting, display, and energy conversion. To sustain advanced applications of organic semiconductor devices, further studies of the physical property of small organic molecules films are important. Therefore, this thesis aims to develop a method of measuring the glass transition temperature of the small organic molecules films.The material used in this study is the small organic molecule 4,4’,4"-Tri(Ncarbazolyl) triphenylamine (TCTA). The samples of films are produced by vacuum thermal evaporation. The thickness and optical constants at different temperatures are measured by the spectroscopic ellipsometer. An abrupt change in the thickness and refractive index (n, k) as a function temperature are observed.. This change is caused by the glass transition temperature of organic small molecule films. Besides, the glass transition temperatures of the small organic molecules decrease in exponential relationship with the increase of its thickness. The thermal expansion coefficient of the TCTA films before and after glass transition temperature differs 2-9 times. It is also found the maximum deviation of glass transition temperature based on the sudden change of refractive index is only 2.0℃. This proves that the change of refractive index is also a reliable and accurate method to measure glass transition temperature.This thesis reports an experimental ellipsometer-based method of measuring the glass transition temperatures of the organic small molecules films. Compared to the traditional Differential Scanning Calorimetry in measuring glass transition temperature, this method is simple, accurate and reliable. This research findings in this thesis provides an effective method for the studies in glass transition temperatures of the small organic molecules films. |
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