紅熒烯與肽菁銅混合有機薄膜之物性量測與電晶體之應用

Mixed Organic Thin Films of Copper Phthalocyanine and Rubrene: Characterization and Transistor Application

游定書(Ting-Shu Yu)

指導教授 ： 楊耀文

國立清華大學/理學院/化學系/碩士(2012年)

https://doi.org/10.6843/NTHU.2012.00213

摘要

本論文旨在利用混合式蒸鍍有機薄膜的概念，選擇單晶態下具有最高電傳效益的紅熒烯(rubrene)與易形成晶性有機薄膜的肽菁銅(CuPc)，於兩種修飾層分子上製備混合式結構的薄膜。透過原子力顯微鏡(AFM)、X光光電子能譜(XPS)、X光繞射(XRD)與近緣X光吸收細微結構光譜術(NEXAFS)對此種混合薄膜的表面形貌、薄膜中分子個數組成比例、晶相結構與分子位向等方面進行探討。以歸結出紅熒烯與肽菁銅在混合過程中的成長模式，由成長模式來探討元件的效能表現。
由XPS的量測結果發現此混合式薄膜近表層的分子個數組成大致維持一固定比例，表示此兩分子非以混合均勻的結構存在。同時透過XRD的分析了解混合式薄膜，未生成新的晶相結構，表示此兩種分子無法形成任意比例的新晶相結構。由NEXAFS量測結果中發現肽菁銅分子於兩種修飾層上的成長具有不同的分子變化，以三氯十八矽烷(OTS)為修飾層而言，肽菁銅分子在高比例紅熒烯混合下，會有分子傾角增大的情形；而以4-丁基苯基三氯矽烷(4-PBTS)為修飾層分子的話，能維持住肽菁銅分子原本的傾角。當薄膜表層以一固定混合比例存在時，其餘分子往底層沉降之後，底層形貌發生了變化，令上層混合薄膜內晶相結構受到影響。對OTS為修飾層而言，其底層形貌屬於非晶相的不平整且凌亂結構，致使上層薄膜晶相受到削弱。另以4-PBTS為修飾分子而論，底層是形貌相對平整且非完全凌亂的結構，故可允許上層混合薄膜中的晶相結構受底層的干擾情形較少，對於晶性與分子環面的傾角維持相對容易。
透過以混合有機薄膜製成場效電晶體後的電性量測結果，發現以4-PBTS為修飾層的元件效能優於以OTS修飾者。此時透過AFM影像上的分析，可發現以4-PBTS作基材修飾的元件，具有的條狀特徵橫截寬度較大，表示晶體尺寸於此基材上有增大的效果，同時於此種基材上所得到各種混合比例中平均載子遷移率最高者可達5.9×10–2 cm2V–1s–1。此遷移率同時高於以同樣基材所製成肽菁銅薄膜元件的效能表現，表示以此混合方式製備的肽菁銅與紅熒烯混合薄膜，相對於二種分子中的任一種更適合於追求元件效能上的應用。

關鍵字

肽菁銅 ； 紅熒烯 ； 有機場效電晶體 ； 混合式薄膜

並列摘要

Mixed organic semiconducting thin films were prepared by vacuum-depositing copper phthalocyanine (CuPc) and rubrene of different mixing ratio onto oxide-terminated Si(100) wafers that were pre-modified with self-assembled monolayer (SAM) of either octadecyltrichlorosilane (OTS) or 4-phenylbutyltrichlorosilane (4-PBTS). The thin films were characterized by atomic force microscopy (AFM) and various synchrotron-based techniques such as x-ray photoemission spectroscopy (XPS), x-ray diffraction (XRD), and near-edge x-ray absorption fine structure (NEXAFS) spectroscopy to obtain the information about the thin films in various aspects such as electronic structure, morphology, crystallinity, averaged molecular orientation, etc.
The out-of-plane XRD data show that all the mixed films are composed of CuPc in predominately crystalline from and rubrene in exclusively amorphous form. More informative structural change can be obtained by examining grazing incidence x-ray diffraction (GIXD) images. For pure CuPc film, the a-b plane of CuPc crystallite is found to be parallel to the substrate surface. For the films of increasing rubrene percentage, the CuPC crystallite becomes tilted away from the substrate surface, forming elongated diffraction spots. For the mixed film of the highest rubrene percentage (90%), CuPc crystallites decrease in size, lose surface registry, and become powder-like samples, producing characteristic powder-diffraction rings. In consistence with the structural change documented by x-ray diffraction data, the average tilt angle of CuPc molecules, measured from the surface, also decreases dramatically by up to 10°, as recorded by NEXAFS data. Moreover, there seems to be very little chemical interaction between CuPc and rubrene molecules so as to effect observable changes in XPS N 1s spectra and N K-edge NEXAFS spectra (incidence angle of 55°) for CuPc of different mixed films.
Organic field effect transistors based on the aforementioned mixed semiconducting films were fabricated. For mixed-film OFET, a modest mobility of at least 2 × 10–2 cm2/Vs can all be obtained, with the best value of 5.9×10–2 cm2/Vs obtained for the mixed film of 75% CuPc+25 % rubrene grown on 4-PBTS substrate. Comparing the AFM images with mobility data, we found that a larger width in the characteristic CuPc features in AFM image seems to give better electrical performance, suggesting a beneficial effect exerted by the larger CuPC grains.

並列關鍵字

copper phthalocyanine ； rubrene ； OFET ； mixed thin film

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