Electronic structures at organic heterojunctions of N,N'-bis(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamin (NPB)-based organic light emitting diodes
Electronic structures at organic heterojunctions of N,N'-bis(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamin (NPB)-based organic light emitting diodes
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N,N-双(1-萘基)-N,N-二苯基-1,1-联苯-4,4-二胺(NPB)基有机发光二极管有机异质结的电子结构
DOI：
10.1016/j.orgel.2012.08.033
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发表时间：
2012
影响因子：
3.2
通讯作者：
Hisao Ishii
中科院分区：
文献类型：
--
作者：
Yasuo Nakayama;Shin'ichi Machida;Yukimasa Miyazaki;Tatsuhiko Nishi;Yutaka Noguchi;Hisao Ishii
用光电子能谱(PES)研究了4种电子传输或空穴阻挡有机材料(n型)在有机电致发光二极管(OLED)中广泛应用的空穴传输材料(p型)N，N‘-双(1-萘基)-N，N’-二苯基-1，1‘-联苯-4，4’-二胺(NPB)上的界面电子结构。1，3-bis[5-(4-tert-butylphenyl)-1，3，4-oxadiazole-2-yl]benzene(OXD-7)和2，2′，2″-(1，3，5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole)(TPBi)覆盖层表现出每个覆盖层派生的光谱分量的连续能量移动，真空度与厚度成正比。这种能量转移归因于有机层内静电势的自发建立(巨表面势；GSP)。充分考虑了GSP引起的覆盖层能量移动和界面真空能级移动，确定了异质结处空穴电导能级的实际势垒高度。4，4‘-双(9-咔唑基)联苯(CBP)和对-双(三苯基硅基)苯(UGH2)在NPB薄膜中引起能带弯曲，这可能是NPB向n型材料的电荷转移(CT)所致。尽管没有实际的真空能级移动和覆盖层衍生电子态的厚度相关移动，但NPB的CT衍生能级移动相对于名义势垒高度降低了实际能垒高度，该高度仅由每种材料的厚覆层的PES光谱解释。基于上述对PES光谱的解释，精细地确定了这些n-on-p有机-有机异质结的能级图。
Interface electronic structures of four-kinds of electron transporting or hole blocking organic materials (n-type) on a widely-used hole transporting material (p-type) in organic light emitting diodes (OLEDs), N,N′-bis (1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamin (NPB), were investigated by means of photoelectron spectroscopy (PES). 1,3-bis[5-(4-tert-butylphenyl)-1,3,4-oxadiazole-2-yl]benzene (OXD-7) and 2,2′,2″-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi) overlayers show continuous energy shift of each overlayer-derived spectral components and the vacuum level proportional to the thickness. This energy shift is ascribed to a spontaneous building up of the electrostatic potential within the organic layers (giant surface potential; GSP). The energy shift of the overlayers induced by GSP as well as the interface vacuum level shift are adequately taken into account to determine the actual energy barrier heights of the hole conduction levels at the heterojunctions. 4,4′-bis(9-carbazolyl)biphenyl (CBP) and p-bis(triphenylsilyl) benzene (UGH2) induce band bending in the NPB film which presumably results from charge transfer (CT) to the n-type materials from NPB. Despite absence of a practical vacuum level shift and thickness dependent shift of the overlayer-derived electronic states, the CT-derived energy shift of NPB reduces the actual energy barrier height with respect to the nominal barrier height being simply interpreted from PES spectra of a thick overlayer of each material. The energy level diagrams across these ‘n-on-p’ organic–organic heterojunctions were finely determined based on the above interpretation of the PES spectra.