全氟化离聚物修饰的空穴注入层：超高功函数但非欧姆接触,Advanced Functional Materials

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全氟化离聚物修饰的空穴注入层：超高功函数但非欧姆接触
Advanced Functional Materials ( IF 18.5 ) Pub Date : 2015-08-04 , DOI: 10.1002/adfm.201500784
Dagmawi Belaineh ₁ , Jun-Kai Tan ₁ , Rui-Qi Png ₁ , Pei-Fang Dee ₁ , Yi-Min Lee ₁ , Bao-Nguyen Nguyen Thi ₁ , Nur-Sabrina Ridzuan ₁ , Peter K. H. Ho ₁

Affiliation

最近有报道称，Nafion低聚物，即2-（2-磺基四氟乙氧基）-2-三氟甲基三氟乙氧基官能化的低聚四氟乙烯，也称为全氟离聚物（PFI），可以掺混到聚（3,4-亚乙基二氧噻吩）：聚（苯乙烯磺酸）中（PEDT：PSSH）电影，以将其工作功能提高到5.2 eV以上。这些经过PFI改性的薄膜可用于能级对准研究，并已被建议用作空穴注入层（HIL）。但是，这里显示出，这些HIL不能提供足够快的空穴传输到电离势深于≈5.2 eV的相邻聚合物半导体层中。X射线和紫外光发射光谱表明，这些HIL表现出分子薄的PFI覆盖层，该覆盖层建立了表面偶极子，从而提供了超高的功函。该偶极层即使在随后的有机半导体层沉积时也能持续存在，这可以通过二极管内置电势的测量来证明。结果，经过PFI修饰的HIL产生的接触电阻更高，并且半导体触点处的空穴平衡密度也比通过减少空穴注入势垒的简单热力学考虑所预期的要低。因此，在电荷注入触点处使用绝缘的偶极表面层来调节其功函数以匹配半导体的相关传输水平，对于在这些器件中实现欧姆接触的实用性有限。PFI修饰的HIL产生的接触电阻更高，并且半导体触点处的空穴平衡密度也比通过简单的热力学考虑来减少空穴注入势垒所期望的要低。因此，在电荷注入触点处使用绝缘的偶极表面层来调节其功函数以匹配半导体的相关传输水平，对于在这些器件中实现欧姆接触的实用性有限。PFI修饰的HIL产生的接触电阻更高，并且半导体触点处的空穴平衡密度更低，这是因为从简单的热力学考虑减少了空穴注入势垒。因此，在电荷注入触点处使用绝缘的偶极表面层来调节其功函数以匹配半导体的相关传输水平，对于在这些器件中实现欧姆接触的实用性有限。

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Perfluorinated Ionomer‐Modified Hole‐Injection Layers: Ultrahigh‐Workfunction but Nonohmic Contacts

Recently it has been reported that Nafion oligomers, i.e., 2‐(2‐sulfonatotetrafluoroethoxy)‐2‐trifluoromethyltrifluoroethoxyfunctionalized oligotetrafluoroethylenes, also called perfluorinated ionomers (PFIs), can be blended into poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDT:PSSH) films to increase their workfunctions beyond 5.2 eV. These PFI‐modified films are useful for energy‐level alignment studies, and have been proposed as hole‐injection layers (HILs). It is shown here however that these HILs do not provide sufficiently fast hole transfer into adjacent polymer semiconductor layers with ionization potentials deeper than ≈5.2 eV. X‐ray and ultraviolet photoemission spectroscopies reveal that these HILs exhibit a molecularly‐thin PFI overlayer that sets up a surface dipole that provides the ultrahigh workfunction. This dipolar layer persists even when the subsequent organic semiconductor layer is deposited, as evidenced by measurements of the diode built‐in potentials. As a consequence, the PFI‐modified HILs produce a higher contact resistance, and a lower equilibrium density of holes at the semiconductor contact than might have been expected from simple thermodynamic considerations of the reduction in hole‐injection barrier. Thus the use of insulating dipolar surface layers at the charge‐injection contact to tune its workfunction to match the relevant transport level of the semiconductor is of limited utility to achieve ohmic contact in these devices.

更新日期：2015-08-04

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