熱致交聯共軛高分子在有機場效電晶體之應用及元件壽命之測量

Thermally crosslinkable conjugated polymers for use in organic field-effect transistors and lifetime measurement

廖明志(Ming-Jhih Liao)

指導教授 ： 崛江正樹

國立清華大學/工學院/化學工程學系/碩士(2017年)

摘要

為了提升有機場效電晶體的元件表現及其元件壽命，在此研究中，我們製備了 PBDTTPD 及 PTB7-Th 以及其交聯高分子 Cr-PBDTTPD 和 Cr-PTB7-Th並利用此材料來比較其元件表現及壽命，並探究其中的原因為何。在合成熱交聯高分子的過程中，加入5 mol% 含有1-hexenyl group的cyclopentadithiophene (CPDT)單體，並利用heck coupling reaction 及4-bromoanisole的導入將熱交聯單體上的allyl group置換成 anisole group 使其能夠在較低溫下產生交聯反應。此外，為了與非交聯共軛高分子做對照，我們也利用紫外光/可見光光譜儀和循環伏安法做材料的光學以及電化學性質上的定性分析。
合成完高分子材料以後，此材料用於製備有機場效電晶體。製備的過程中，對高分子材料層進行不同溫度的退火處理( 105 °C, 140°C, 160°C,以及180°C)。並比較在最佳載子遷移率下的元件壽命。PBDTTPD及Cr-PBDTTPD 分別在180°C和160 °C時呈現最佳的元件表現。然而，在經過退火處理後PBDTTPD呈現最佳元件壽命表現。另外，在加入熱交聯單體後，Cr-PTB7-Th的載子移動率下滑，PTB7-Th及Cr-PTB7-Th則分別在180°C和160 °C時呈現最佳的元件表現。在退火處理後，Cr-PTB7-Th呈現較佳元件壽命表現，此乃由於熱交聯反應的發生，使元件穩定性提高。為了探究造成此現象差別的原因，我們利用X光繞射分析儀和原子力顯微鏡，觀察高分子薄膜內的材料排列情形及表面的組態。並以此分析觀察退火處理前後，高分子薄膜內材料排列及表面組態間的差異，以探討如何提升元件壽命。
此外，以低成本和高元件表現著稱的PTAA，在此研究中，不同的分子量、純化方法以及處理方式的PTAA，也被用於測量及比較OFET的元件壽命。經過鹼處理的PTAA有最好的元件表現。此外，XPS電子能譜儀也被用於探就不同PTAA間的化學環境變化。

關鍵字

共軛高分子 ； 交聯高分子 ； 有機場效電晶體 ； 元件壽命

並列摘要

In this work, we have synthesized crosslinkable and non-crosslinkable conjugated polymers for use in organic field-effect transistors (OFETs). Poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b']dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-)-2-carboxylate-2-6-diyl)] (PTB7-Th) and poly[[5-(2-ethylhexyl)-5,6-dihydro-4,6-dioxo-4H-thieno[3,4-c] pyrrole-1,3-diyl][4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl]] (PBDTTPD) are selected as our synthetic targets because these polymers have been used to fabricate high performing organic photovoltaics (OPVs) and OFETs. To synthesize crosslinkable polymers, 5 mol% of dibromo-cyclopentadithiophene (CPDT) which contains crosslinkable 1-hexenyl group is added as a monomer during polymerization. After the polymerization, Heck reaction is used to cap the allyl groups with 4-bromoanisole. Solubility of the crosslinkable polymers are tested after heating the polymer films at 160 °C for 16 hours. There are lots of insoluble particles which cannot be dissolved in chloroform. In order to discuss effects of the crosslinking on fundamental properties and OFET performances of the polymers, non-crosslinkable polymers (PTB7-Th and PBDTTPD) are also synthesized. Optical and electrochemical properties of the polymers are analyzed by UV-visible spectroscopy and cyclic voltammetry (CV). The crosslinkable polymers show very similar properties to non crosslinkable polymers, indicating that crosslink agent does not change the original optical and electrochemical properties.
These polymers are used for OFET fabrication. non-crosslinkable PBDTTPD shows hole mobility of 2.9 x 10-5 cm2 V-1 s-1. After annealing at 180 °C for 1 hour, mobility is enhanced up to 5.3 x 10-5 cm2 V-1 s-1. Corresponding crosslinkable polymer Cr-PBDTTPD shows hole mobility of 5.6 x 10-5 cm2 V-1 s-1, which is changed to 9.4 x 10-5 cm2 V-1 s-1 after annealing at 160 °C for 1 hour. The device fabricated using PBDTTPD (annealed at 180 °C for 1 hour) shows high stability. This is due to crystalline nature of PBDTTPD. Lifetime of Cr-PBDTTPD device is improved a little by the crosslinking.
PTB7-Th shows hole mobility of 3.1 x 10-3 cm2 V-1 s-1 which is higher than Cr-PTB7-Th (1.1 x 10-3 cm2 V-1 s-1). After annealing at 160 °C for 1 hour, Cr-PTB7-Th shows mobility up to 1.9 x 10-3 cm2 V-1 s-1. On the other hand, PTB7-Th shows mobility up to 3.6 x 10-3 cm2 V-1 s-1 after annealed at 180 °C for 1 hour. Furthermore, lifetime of Cr-PTB7-Th which was annealed at 160 °C for 1 hour is enhanced nearly 1.5 times compared to that of Cr-PTB7-Th before crosslinking.
In addition, poly(triarylamine)s (PTAAs), which are known as a low cost and high performance polymers, are selected for the OFET lifetime measurement. PTAAs with various molecular weight are obtained via polyamination, followed by purification using preparative gel permeation chromatography and base treatment. Device stability of these PTAAs is compared. As a result, PTAA with base treatment shows highest mobility (1.1 x 10-4 cm2 V-1 s-1). X-ray photoelectron spectra are measured to investigate the chemical changes of various PTAAs.

並列關鍵字

conjugated polymer ； crosslink polymer ； organic field effect transistor ； device lifetime

參考文獻

3. Søndergaard, R.R.;Hösel, M.Krebs, F.C., J. Polym. Sci. B Polym. Phys., 2013, 51, 16.

11. Milstein, D.Stille, J.K., J. Am. Chem. Soc., 1978, 100, 3636.

13. Nicolaou, K.C.;Bulger, P.G.Sarlah, D., Angew. Chem. Int. Ed., 2005, 44, 4442.

15. Miyaura, N.Suzuki, A., J. Chem. Soc. Chem. Comm., 1979, 866.

16. Heck, R.F.Nolley, J.P., J. Org. Chem., 1972, 37, 2320.