有机光电器件的界面特性研究
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摘要
近些年来，有机光电器件由于其具有成本低，重量轻、材料容易设计合成、可做成大面积，显示柔性易弯曲折叠、制备过程简单等优点引起了越来越多的关注。各种功能的有机光电器件相继被开发出来，例如有机发光二极管可以用在平板显示和固态照明，有机光伏电池作可以作为清洁可再生的能源可有效缓解当前社会的能源需求，有机场效应晶体可用来作为显示背板和智能卡片，还有有机存储，传感器等等显示了巨大的应用前景。在有机光电器件中，界面对器件的性能和工作寿命有重要的影响。虽然我们在有机光电器件领域已经取得了重大的突破进展，但由于在有机界面中存在界面偶极、电子极化、电荷转移激子等现象，传统的无机半导体理论不能完全适用于有机界面，对有机界面的物理机制缺乏清晰的认识，限制了有机光电器件的进一步发展，因此有必要对有机界面进行深入的研究进一步理解其深层的物理机制。
本文主要通过光电子能谱技术，对叠层有机光电器件中间连接层、正置和倒置结构有机光伏电池的界面电子结构和能级排列进行了系统的研究，此外还研究了电学掺杂、基底修饰和不同电子传输层对界面势垒的调控影响以及退火处理对有机异质结薄膜表面和界面电子结构的影响。具体内容如下：
（1）叠层有机光电器件的中间连接层界面电子结构和能级排列
对采用有机HATCN为中间连接层p型材料的中间连接层的界面电子结构：(a) MADN/NPB,(b) Li:Bphen/NPB,(c) HATCN/NPB,(d) Li:Bphen/HATCN/NPB的能级排列进行了对比分析，讨论了HATCN和Li:Bphen在中间连接层的作用；在此基础上了利用Bphen和TPBI替代MADN制备了高效稳定的白光有机发光器件，分析了界面能级排列和电子注入对器件的影响，最后研究了叠层有机光伏电池的中间连接层(a) Bphen/SubPc,(b) HATCN/SubPc,(c) Li:Bphen/SubPc,(d)Li:Bphen/HATCN/SubPc的界面电子结构和能级排列，分析了界面连接层对有机光伏电池的影响。
（2）界面调控对电子注入势垒的影响
首先研究了不同浓度CsF掺杂Alq3的电子结构，分析了n型掺杂电子传输层对电子注入势垒的影响，接着分析了不同电子传输层材料的界面能级排列以及对电子注入势垒的影响，最后研究了基底修饰的ITO界面的能级排列，分析了基底修饰对界面电子结构的影响。
（3）正置和倒置结构有机光伏电池的界面电子结构和能级排列
通过UPS研究了SubNc/C60, MoO3/SubNc/C60, Cs2CO3/SubNc/C60，和C60/SubNc,MoO3/C60/SubNc, Cs2CO3/C60/SubNc界面的电子结构和能级排列，分析了MoO3和Cs2CO3对界面能级的作用以及正置和倒置结构能级排列的不同，用SubPc代替SubNc，研究了SubPc/C60, MoO3/SubPc/C60, Cs2CO3/SubPc/C60和C60/SubPc,MoO3/C60/SubPc, Cs2CO3/C60/SubPc界面的电子结构和能级排列，分析MoO3和Cs2CO3对不同材料界面能级的作用以及正置和倒置结构能级排列的不同，并进一步制备了对应的器件来验证理论分析结果。（4）退火对有机体薄膜界面特性的影响
研究了CuPc/C60, TiOPc/C60, PTCDA/C60和CuPc:C60, TiOPc:C60, PTCDA:C60薄膜在不同退火温度下的电子结构，分析了退火处理对不同结构的材料有机薄膜表相分离的影响。在此基础上，用PTCDA代替C60，研究了CuPc/PTCDA，CuPc:PTCDA和TiOPc/PTCDA, TiOPc:PTCDA退火后的电子结构变化，验证了分子结构对退火过程中相分离的影响。
Organic electronics have been attracted intensive and increasing attention in thepast two decades due to their potential advantages of low cost, compatibility with largearea and flexible substrates，versatile chemical design and synthesis, light weight andease of fabrication. Fully functional devices including organic light-emitting diodes(OLEDs), organic photovoltaic cells (OPVs), organic field-effect transistors (OFETs),photodetectors and memory have all been demonstrated and show great prospects ininformation techonology application. For example，OLEDs can be used for flat paneldisplays and solid-state Lighting, OPVs as a renewable and clean energy can effectivelyalleviate the current energy needs of the community and OFETs can be used to fabricatethe display backplanes and smart cards. It is widely recognized that the interface play animportant role in determine the performance and lifetime of organic electronic devices.Despite impressive breakthroughs in organic electronics technology have been achieved,a thorough understanding of the underlying physics within organic devices is stilllacking because of the formation of interface dipole, electronic polarization andcharge-transfer excitons in the organic interface. It is not applicable to accuratelydescribe and predictthe interfacial electronic structures and energy level alignment withconventional models in inorganic semiconductors. Therefore, it is necessary toinvestigate the organic interface to get a deep understanding of the underlying physicalmechanisms.
In this thesis, the interface electronic structure and energy level alignment of theinterconnector in tandem organic electronics devices and OPV devices with normal andinverted structures have been systematically investigated by ultraviolet and X-rayphotoemission spectroscopies (UPS and XPS). In addation, the effect of electrical doping, substrate modification and electron transport layer on the interfacial barrier andthe characteristics of the organic heteojunction films after thermal annealing also havebeen studied. More details are listed below:
(1) Interfacial electronic structures and energy alignments of interconnectors in tandemorganic electronic devices
The interfacial electronic structures and energy level alignments of intermediateconnectors using HATCN as p-type layer, including (a) MADN/NPB,(b)Li:Bphen/NPB,(c) HATCN/NPB,(d) Li:Bphen/HATCN/NPB were studied via UPSand XPS. The function of Li:Bphen and HATCN in the interconnectors was discussedby analysing the energy level alignment. Based on the above results, high efficient andstable white light emitting diode was fabricated using TBPI and Bphen as replacementof MADN to see the effect of electron injection on device performance. Finally, theeffect of interconnectors including (a) Bphen/SubPc,(b) HATCN/SubPc,(c)Li:Bphen/SubPc,(d) Li:Bphen/HATCN/SubPc on the tandem OPV devices werediscussed by studying the interfacial electronic structures and energy level alignments.
(2) Effect of interfacial tuning on the injection barrier
The effect of electrical doping on the electron injection barrier was discussed bystudying the electronic structure and energy level alignment of CsF:Alq3films withdifferent doping concentration. Next, the electronic structures of different electrontransport layers (ETL) were studied via XPS and UPS. The effect of ETL on theinjection and device performance was investigated by combine the electronic structureand energy level alignment. The electronic structures of organic film on modified ITOsubstrates were aslo investigated via XPS and UPS.
(3) Interfacial electronic structures and energy alignments of organic photovoltaic cellswith normal and inverted structures
The Interfacial electronic structures and energy alignments between SubNc/C60,MoO3/SubNc/C60, Cs2CO3/SubNc/C60, and C60/SubNc, MoO3/C60/SubNc,Cs2CO3/C60/SubNc were studied via XPS and UPS. The differences between nomal andinverted structures with MoO3and Cs2CO3were discussed. The Interfacial electronic structure and energy alignment of SubPc intead of SubNc were also studied toinvestigate the impact of device strcture with MoO3and Cs2CO3on the interfacialelectronic structure and energy level alignment. The corresponding devices were alsofabricated to validate the above analysis.
(4) Effect of thermal annealing on the organic film
The electronic structures of CuPc/C60, TiOPc/C60, PTCDA/C60bilayers andCuPc:C60, TiOPc:C60, PTCDA:C60mixed films were studied by XPS and UPS. Adetailed analysis of phase separation between organic films with different molecularstructures was gived based on the XPS and UPS results. Then the electronic structuresof CuPc/PTCDA，CuPc:PTCDA and TiOPc/PTCDA, TiOPc:PTCDA were also studiedto prove the relations between molecular structures and phase separation.
本文主要通过光电子能谱技术，对叠层有机光电器件中间连接层、正置和倒置结构有机光伏电池的界面电子结构和能级排列进行了系统的研究，此外还研究了电学掺杂、基底修饰和不同电子传输层对界面势垒的调控影响以及退火处理对有机异质结薄膜表面和界面电子结构的影响。具体内容如下：
（1）叠层有机光电器件的中间连接层界面电子结构和能级排列
对采用有机HATCN为中间连接层p型材料的中间连接层的界面电子结构：(a) MADN/NPB,(b) Li:Bphen/NPB,(c) HATCN/NPB,(d) Li:Bphen/HATCN/NPB的能级排列进行了对比分析，讨论了HATCN和Li:Bphen在中间连接层的作用；在此基础上了利用Bphen和TPBI替代MADN制备了高效稳定的白光有机发光器件，分析了界面能级排列和电子注入对器件的影响，最后研究了叠层有机光伏电池的中间连接层(a) Bphen/SubPc,(b) HATCN/SubPc,(c) Li:Bphen/SubPc,(d)Li:Bphen/HATCN/SubPc的界面电子结构和能级排列，分析了界面连接层对有机光伏电池的影响。
（2）界面调控对电子注入势垒的影响
首先研究了不同浓度CsF掺杂Alq3的电子结构，分析了n型掺杂电子传输层对电子注入势垒的影响，接着分析了不同电子传输层材料的界面能级排列以及对电子注入势垒的影响，最后研究了基底修饰的ITO界面的能级排列，分析了基底修饰对界面电子结构的影响。
（3）正置和倒置结构有机光伏电池的界面电子结构和能级排列
通过UPS研究了SubNc/C60, MoO3/SubNc/C60, Cs2CO3/SubNc/C60，和C60/SubNc,MoO3/C60/SubNc, Cs2CO3/C60/SubNc界面的电子结构和能级排列，分析了MoO3和Cs2CO3对界面能级的作用以及正置和倒置结构能级排列的不同，用SubPc代替SubNc，研究了SubPc/C60, MoO3/SubPc/C60, Cs2CO3/SubPc/C60和C60/SubPc,MoO3/C60/SubPc, Cs2CO3/C60/SubPc界面的电子结构和能级排列，分析MoO3和Cs2CO3对不同材料界面能级的作用以及正置和倒置结构能级排列的不同，并进一步制备了对应的器件来验证理论分析结果。（4）退火对有机体薄膜界面特性的影响
研究了CuPc/C60, TiOPc/C60, PTCDA/C60和CuPc:C60, TiOPc:C60, PTCDA:C60薄膜在不同退火温度下的电子结构，分析了退火处理对不同结构的材料有机薄膜表相分离的影响。在此基础上，用PTCDA代替C60，研究了CuPc/PTCDA，CuPc:PTCDA和TiOPc/PTCDA, TiOPc:PTCDA退火后的电子结构变化，验证了分子结构对退火过程中相分离的影响。
Organic electronics have been attracted intensive and increasing attention in thepast two decades due to their potential advantages of low cost, compatibility with largearea and flexible substrates，versatile chemical design and synthesis, light weight andease of fabrication. Fully functional devices including organic light-emitting diodes(OLEDs), organic photovoltaic cells (OPVs), organic field-effect transistors (OFETs),photodetectors and memory have all been demonstrated and show great prospects ininformation techonology application. For example，OLEDs can be used for flat paneldisplays and solid-state Lighting, OPVs as a renewable and clean energy can effectivelyalleviate the current energy needs of the community and OFETs can be used to fabricatethe display backplanes and smart cards. It is widely recognized that the interface play animportant role in determine the performance and lifetime of organic electronic devices.Despite impressive breakthroughs in organic electronics technology have been achieved,a thorough understanding of the underlying physics within organic devices is stilllacking because of the formation of interface dipole, electronic polarization andcharge-transfer excitons in the organic interface. It is not applicable to accuratelydescribe and predictthe interfacial electronic structures and energy level alignment withconventional models in inorganic semiconductors. Therefore, it is necessary toinvestigate the organic interface to get a deep understanding of the underlying physicalmechanisms.
In this thesis, the interface electronic structure and energy level alignment of theinterconnector in tandem organic electronics devices and OPV devices with normal andinverted structures have been systematically investigated by ultraviolet and X-rayphotoemission spectroscopies (UPS and XPS). In addation, the effect of electrical doping, substrate modification and electron transport layer on the interfacial barrier andthe characteristics of the organic heteojunction films after thermal annealing also havebeen studied. More details are listed below:
(1) Interfacial electronic structures and energy alignments of interconnectors in tandemorganic electronic devices
The interfacial electronic structures and energy level alignments of intermediateconnectors using HATCN as p-type layer, including (a) MADN/NPB,(b)Li:Bphen/NPB,(c) HATCN/NPB,(d) Li:Bphen/HATCN/NPB were studied via UPSand XPS. The function of Li:Bphen and HATCN in the interconnectors was discussedby analysing the energy level alignment. Based on the above results, high efficient andstable white light emitting diode was fabricated using TBPI and Bphen as replacementof MADN to see the effect of electron injection on device performance. Finally, theeffect of interconnectors including (a) Bphen/SubPc,(b) HATCN/SubPc,(c)Li:Bphen/SubPc,(d) Li:Bphen/HATCN/SubPc on the tandem OPV devices werediscussed by studying the interfacial electronic structures and energy level alignments.
(2) Effect of interfacial tuning on the injection barrier
The effect of electrical doping on the electron injection barrier was discussed bystudying the electronic structure and energy level alignment of CsF:Alq3films withdifferent doping concentration. Next, the electronic structures of different electrontransport layers (ETL) were studied via XPS and UPS. The effect of ETL on theinjection and device performance was investigated by combine the electronic structureand energy level alignment. The electronic structures of organic film on modified ITOsubstrates were aslo investigated via XPS and UPS.
(3) Interfacial electronic structures and energy alignments of organic photovoltaic cellswith normal and inverted structures
The Interfacial electronic structures and energy alignments between SubNc/C60,MoO3/SubNc/C60, Cs2CO3/SubNc/C60, and C60/SubNc, MoO3/C60/SubNc,Cs2CO3/C60/SubNc were studied via XPS and UPS. The differences between nomal andinverted structures with MoO3and Cs2CO3were discussed. The Interfacial electronic structure and energy alignment of SubPc intead of SubNc were also studied toinvestigate the impact of device strcture with MoO3and Cs2CO3on the interfacialelectronic structure and energy level alignment. The corresponding devices were alsofabricated to validate the above analysis.
(4) Effect of thermal annealing on the organic film
The electronic structures of CuPc/C60, TiOPc/C60, PTCDA/C60bilayers andCuPc:C60, TiOPc:C60, PTCDA:C60mixed films were studied by XPS and UPS. Adetailed analysis of phase separation between organic films with different molecularstructures was gived based on the XPS and UPS results. Then the electronic structuresof CuPc/PTCDA，CuPc:PTCDA and TiOPc/PTCDA, TiOPc:PTCDA were also studiedto prove the relations between molecular structures and phase separation.
引文
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