調變可溶性有機薄膜之微晶體位相及摻雜電子受體來提升有機薄膜電晶體效能

Improving Organic Thin-Film Transistor Performance by Controlling the Orientation of Solution-Processible Microcrystallites and Doping with Electron Acceptor.

李伶如(Ling-Ru Li)

指導教授 ： 楊耀文

國立清華大學/理學院/化學系/碩士(2011年)

https://doi.org/10.6843/NTHU.2011.00228

摘要

本論文主要著重於製作高效能的有機薄膜場效電晶體(OTFTs)，可溶性有機半導體薄膜分別藉由退火與摻雜處理，並探討其結晶性質與各介面對有機薄膜場效電晶體效能的影響，期待能製作高效能元件。挑選的可溶性p型有機半導體分子為2,8-difluoro-5,11-bis- (triethylsilylethynyl) anthradithiophene (diF-TESADT)，實驗分成二個部分：
第一部分著重於利用退火處理(post annealing)改善有機薄膜結晶性質。不同退火條件處理的薄膜分別藉由原子力顯微鏡(Atomic Force Microscope，AFM)、X光繞射(X-Ray Diffraction，XRD)、掠角入射X光繞射(Grazing Incidence X-Ray Diffraction)、與近緣X光吸收細微結構(Near-Edge X-Ray Absorption Fine Structure，NEXAFS)觀察其表面形貌、結構、結晶性變化。旋轉塗佈完成後的薄膜的形貌呈現稻穗狀分佈。掠角入射X光繞射清楚顯示此薄膜是由二種不同傾角的晶粒所構成。一是以(001)面法線齊一的排列，另一種是以(111)面法線齊一的排列。此混和排列的薄膜所製作的電晶體其載子遷移率不高，約在10-3 cm2V-1s-1左右，最高為0.37 cm2V-1s-1。經溶劑蒸氣再結晶輔以加熱退火處理後的diF-TESADT薄膜的成長形貌由原本稻穗狀變成大片連續層狀結構，薄膜平面方向進行大規模結構重整，從(111)轉變成適於晶體延展與有利載子跳度的(001)面齊一法線的排列形式。同時也提升了沿著法線方向的結晶性。因而使元件載子遷移率平均值提升至1.39 cm2V-1s-1，最高至2.7 cm2V-1s-1。
第二部分則利用具有拉電子特性的有機分子2,3,5,6-tetrafluoro-7,7,8,8-tetra cyanoquinodimethane (F4-TCNQ)作為摻雜物(dopant)，藉以改善以diF-TESADT為主的有機薄膜場效電晶體之介面偶極效應，進而優化電性表現。藉由紫外光光電子能譜(Ultraviolet Photoemission Spectroscopy，UPS)、X光光電子能譜(X-Ray Photoemission Spectroscopy，XPS)、NEXAFS、AFM討論能階變化、形貌、電性表現的關係。以F4-TCNQ摻雜的diF-TESADT薄膜作為有效傳輸層(active layer)製作成有機薄膜場效電晶體(OTFTs)，特定的摻雜比例可大幅降低臨界電壓(threshold voltage，VTH)，推測F4-TCNQ的拉電子特性對有機場效電晶體的介面偶極有中和的效果，使VTH由21.3 V降至1.47 V；但過量的F4-TCNQ則會扮演雜質，阻礙晶體的延展。

關鍵字

有機薄膜場效電晶體 ； HASH(0x9d68b10) ； HASH(0x9d68b88) ； 退火處理

並列摘要

In the thesis, we detail the progress made in improving the thin films of 2,8-difluoro-5,11-bis (triethylsilylethynyl) anthradithiophene (diF-TESADT) for high mobility OFET application.
In part (I) experiment, different post-annealing methods were used to improve the organic thin film structure. Morphology, structure, and crystallinity of diF-TESADT films are of particular concern and investigated by combined techniques of atomic force microscopy (AFM), grazing-incidence x-ray diffraction (GIXD), and near-edge x-ray absorption fine structure (NEXAFS) spectroscopy. The diF-TESADT films produced from spin-coating exhibit wheat-like features and GIXD data reveal the presence of both (001)- and (111)-oriented crystallites on the surface. Despite the mixed orientation, as-grown diF-TESADT can still produce OFET with a best mobility of 0.37 cm2V-1 s-1. Improvement in film quality is achieved by employing solvent annealing followed by thermal annealing. The resultant diF-TESADT films exhibit smooth, plate-like features, and GIXD data show a complete structural transformation to (001)-oriented crystallite, a much favored structure for efficient hole transport. The highest OFET mobility reaches 2.70 cm-1V-1s-1, with the median mobility averaged over 15 devices equal to 1.4 cm-1V-1s-1.
In part (II) experiment, we used the strong electron-acceptor 2,3,5,6-tetrafluoro- 7,7,8,8-tetracyanoquinodimethane (F4-TCNQ), as a dopant in diF-TESADT thin film to improve the charge transfer properties. We investigated how the energy levels of organic semiconducting thin films of diF-TESADT change with the F4-TCNQ dopant concentration with ultraviolet photoemission spectroscopy (UPS) and x-ray photoemission spectroscopy (XPS). The results showed that the shift the energy level of diF-TESADT -0.3 eV. The effect of solvent vapor annealing on the morphology and device performance of thin films was also investigated. When molar dopant ratio of reaches 0.37%, the unvanished plate-like features give a small degradation of mobility but the devices averaged threshold voltage shifts from 21.3 V to 1.47 V. We concluded the dramatic VTH variation is presumably due to the structure reorganization of thin film when post annealing. As a consequence, F4-TCNQ effectively neutralized the residual dipoles at the interface between semiconductor layer and the dielectric substrate.

並列關鍵字

OTFTs ； diF-TESADT ； F4-TCNQ ； post annealing

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