광여기 스펙트로스코피를 이용한 박막 트랜지스터의 고분자 반도체와 유전체 사이 계면에서의 전하 트랩 밀도 조사에 관한 연구

Abstract

The interface between the conjugated polymer film and dielectric surfaces plays a crucial role in the performance of organic field-effect transistors (OFETs), which are promising for flexible electronics applications. In this study, we used photoexcitation spectroscopy to investigate the charge trap density at the interfaces between polymer semiconductor and dielectric of PBTTT C-14 thin film FETs. We treated the SiO2 substrate surface with hexamethyldisilazane (HMDS) and octadecyltrichlorosilane (OTS) to create self-assembled monolayers (SAM) that can improve the interface quality. We found that SAM- treated devices showed 0.5-3 times higher FET mobility than untreated devices. Optical absorption assays and evaluations of threshold voltage fluctuations across a spectrum of wavelengths (1800nm to 400nm) elucidated the efficient excitation of charges from the HOMO to the LUMO. Advanced imaging modalities, including Atomic Force Microscopy (AFM) and 2D Grazing Incidence X-ray Diffraction (2D GIXD), were employed to discern the morphological and molecular configurations within the polymer films. These analyses revealed a more distinct granular structure and a higher degree of molecular packing in the SAM-enhanced samples, indicative of elevated molecular order and crystallinity. This enhancement in molecular architecture corresponded to an upsurge in charge carrier mobility, culminating in the amplification of the electrical attributes of the devices. Moreover, assessments of photo-induced transfer characteristics and Density of States (DOS) substantiated a diminution in subgap states within SAM-treated devices, indicating a decrease in charge trap prevalence and a mitigated influence of defects and impurities.