予體-受體共軛分子有機場效電晶體形貌控制與元件表現分析

Abstract

作為有機場效電晶體應用，以π共軛分子形成的單晶陣列有利於產生高載子遷移率，然而電晶體元件中，製備出高覆蓋率的取向性單晶陣列晶體，為此領域的一大挑戰及努力的目標。本論文研究以聚二甲基矽烷高分子來輔助共軛分子結晶(PDMS-assisted crystal, PAC)來製備元件，此溼式製程是將溶劑滴入交聯性的高分子與基板間隙，高分子逐漸吸收溶劑，增加溶液特定區域快速達到過飽和濃度，在基板上形成高取向性且高覆蓋率的單晶陣列，並藉由溶劑蒸氣擴散法(Solvent vapor diffusion, SVD)以共溶劑的方式來改善PAC製程，提升晶體陣列在矽基板上的完整度，藉此提高載子遷移率。 此外，予體-受體(Donor-Acceptor)共軛分子在光電元件中被廣泛地運用；經由不同的予體-受體組合，分子特性皆有所不同，並加入芳香環加以修飾，以改變EHOMO、ELUMO及能隙等；然而置換共軛分子內的芳香環不但改變分子特性、構型，分子自組裝的行為也有所不同，本研究經由不同的芳香環修飾的共軛分子，利用PAC方法與SVD法來製備極佳的取向性及高覆蓋率的晶體陣列形貌，針對不同晶體形貌對元件表現的影響；而本研究以有機共軛分子FBT-4T、DPP-4T及DPP-6T相互比較共軛核心及延長共軛鏈長度的相互關係，共軛分子DPP-4T在p-型有機電晶體元件中提供0.18 cm2V-1s-1的高載子遷移率，為三者之中最高的元件表現。

In the literature, single-crystals of π-conjugated molecules have delivered charge mobility (μ) comparable to polysilicon in organic field-effect transistors (OFETs). However, preparing highly oriented crystal array of π-conjugated molecules with high channel coverage in the OFETs remains challenging. In this study, a facile PDMS-assisted crystal (PAC) growth method was developed. Utilizing the absorbing abilities of the cross-linked PDMS, supersaturation of π-conjugated molecule solutions will occur at the solution/PDMS contact line, creating a row of nuclei. The consequent crystal growth then generates the well-oriented and highly ordered single-crystal array of π-conjugated molecules. Through solvent vapor diffusion (SVD) method, single crystal arrary with over 90% coverage are provided successfully. Donor-Acceptor conjugated molecules have been widely used in optoelectronic applications. Through changing the D/A combination, the molecular properties such as EHOMO, ELUMO, Eg can be effectively modified. However, replacing the aromatic units in the D-A molecules significantly changes molecular shapes and the self-assembly behaviors of the molecules. To test if the PAC method and SVD method applies to conjugated molecules with distinct self-assembly habits, generation of the crystal array of D-A oligomers-FBT-4T, DPP-4T, DPP-6T. The POM observations clearly show that all the D-A oligomers form well-oriental crystal arrays under the PAC method. The OFET characteristics of two crystal arrays have been measured. The μ and on/off ratio are 0.18 cm2V-1s-1 and 105 for DPP-4T. These OFET performances are better than the spin-casted films, suggesting the well-oriented single crystal provides better electronic performances.