有机-有机界面效应的原位及非原位研究

In situ and Ex situ Investigation of the Organic-Organic Interface Effect

有机-有机异质结构已被广泛应用于各种有机电子器件,包括有机发光二极管(OLEDs)、有机场效应晶体管(OFETs)和有机太阳能电池等。全面理解有机-有机异质结构的界面效应,对于器件的设计和性能优化具有重要意义。然而由于有机半导体具有多样的化学特性以及分子间较弱的范德华力,界面电荷传输特性与有机-有机电子结构、环境气氛等密切相关。在此,我们报道了随着顶层半导体并五苯(pentacene)的沉积,并五苯/酞菁氧钒(VOPc)异质结构的原位实时电学性能监测。结果显示,异质结构晶体管的p型迁移率从0.4 cm2∙V−1∙s^(−1)下降至0.2 cm2∙V−1∙s^(−1),而n型迁移率从0.01 cm2∙V−1∙s^(−1)迅速增加至约0.9 cm2∙V−1∙s^(−1)。这种n型输运行为的增强归因于pentacene向VOPc的界面电子转移效应以及由此导致的VOPc层中陷阱态的填充。此外,非原位实验对比表明,当晶体管制备过程暴露于大气时会明显抑制这种界面电荷转移效应,导致沉积pentacene后n型输运几乎没有得到改善。薄膜形态、开尔文探针力显微镜(KPFM)和X射线光电子能谱(XPS)的结果表明,界面处存在从pentacene到VOPc的电子转移。进一步的密度泛函理论(DFT)计算表明,由于pentacene/VOPc之间较强的相互作用,pentacene往VOPc的电荷转移量约为0.15 e。此外,O_(2)/H2O的存在会抑制这种界面电荷转移效应,这与我们的实验结果一致。本研究通过原位电学表征对有机-有机界面之间的电荷转移效应给出了深入解释,有利于进一步的器件性能优化及界面效应分析。

Organic-organic heterostructures have been widely applied in various organic electronic devices,including organic light-emitting diodes(OLEDs),organic field-effect transistors(OFETs),and organic solar cells.A thorough understanding of the interface effect in these heterostructures is of crucial importance for device design and optimization.However,owing to the diverse chemical properties and weak van der Waals interactions of organic semiconductors,interface charge transport is critically related to the organic-organic electronic structure and environmental atmosphere.Therefore,an in situ real-time investigation of the electrical properties in vacuum could efficiently avoid atmospheric influence and aid determination of the instinct interactions at the organic-organic interface.Herein,we report in situ real-time electrical property monitoring of the pentacene/vanadyl phthalocyanine(VOPc)heterostructure with top layer pentacene growth.The hole mobility of the heterostructure transistors decreases from 0.4 cm2∙V−1∙s^(−1) to approximately 0.2 cm2∙V−1∙s^(−1),while the electron mobility increases rapidly from 0.01 cm2∙V−1∙s^(−1) to approximately 0.9 cm2∙V−1∙s^(−1) as the pentacene thickness increases.This enhanced electron transport is attributed to the interface electron transfer from pentacene to VOPc,leading to filling of trap states in the VOPc layer and an improvement in the charge mobility and n-channel current.In contrast,the ex situ processing results indicate that atmospheric exposure will significantly suppress this charge transfer effect,resulting to a negligible improvement in the electron transport.The film morphology,Kelvin probe force microscopy,and X-ray photoelectron spectroscopy characterizations suggest electron transfer occurs from pentacene to VOPc.Additionally,density functional theory(DFT)calculations confirm that the interaction between pentacene and VOPc is strong and the pentacene molecule tends to transfer electrons to VOPc with a calculated charge transfer value of approximately 0.15 e.Moreover,this interface charge transfer is significantly suppressed with the presence of either O_(2) or H2O,which is highly consistent with our experiment results.In this paper,we provide a clear understanding of the instinct organic-organic interface charge transfer effect by using in situ characterization,which will be helpful for further device performance optimization and analysis.