衬底对PTCDA薄膜结构与电荷输运特性的影响

在不同导电衬底(Au,Al和ITO)上制备了PTCDA薄膜,用XRD和AFM技术研究了PTCDA薄膜的结构和表面形貌。结果表明,薄膜中的大部分PTCDA分子平面与衬底不平行,这表明薄膜垂直方向的电流传导将以电子传输为主;在ITO和Au衬底上生长的PTCDA薄膜晶粒排列规则,在薄膜垂直方向呈现出较好的电子传输性能;而在Al衬底上生长的PTCDA薄膜晶粒排列无序,电子传输性能差。通过制备单层结构有机薄膜器件,研究了PTCDA薄膜垂直方向的电子迁移率。综合应用金属-有机界面的热电子发射理论和有机层体内空间电荷限制传导理论,并考虑电场强度对迁移率变化的影响,对ITO/PTCDA/Al器件的电流密度-电压曲线进行拟合,得到ITO衬底上生长的PTCDA薄膜在垂直方向随电场强度变化的电子迁移率数值。

Effect of Substrate on The Structure and Charge Transport Property of PTCDA Thin Film

Perylene-3,4,9,10-tetracarboxylic acid dianhydride(PTCDA) thin films were vacuum evaporated on Au,Al and ITO substrates,their structure and morphology were analysed by X-ray spectroscopy(XRD) and atomic force microscope(AFM).The results show that most of PTCDA molecules don’t lie parallel to the substrate,which indicates that electron transport dominates the current conduction in the direction perpendicular to the film plane.PTCDA films grown on ITO and Au arrange regularly.It shows good electronic transport properties perpendicular to the film plane.But the grains of PTCDA film grown on Al arrange disorderly resulting in poor performance of electronic conduction.By the thermionic emission theory at metal-organic interface and space charge limited current conduction theory in the organic bulk and considering the electric field effect on mobility,current density-voltage curves of ITO/PTCDA/Al devices were fitted in different PTCDA film’s thickness.The numerical value of electron mobility dependent on electric field was determined for the specific PTCDA film thickness.