||The Fabrication of Flexible Transparent Electrodes and Surface Treatment for Organic Light-Emitting Devices
||Department of Electrical Engineering
||Chen Tao Wang
Anode Buffer Layer
Transparent Conducting Electrodes
第一部分將探討銀網狀電極之表面特性，首先，我們利用黃光製程及熱蒸鍍法來製備六角形的銀網狀電極，先利用品質因子(Figure of Merit, FOM)來確定電極之最佳參數，並利用表面能 (surface energy)及能量色散X-射線光譜 (EDS) 來進行表面分析，發現銀網狀電極會因為空氣中的硫分子產生硫化，進而使得其親水性提高，但單純的銀網狀電極其表面粗糙度仍然非常高，因此在第二部分將會對粗糙度的部分來做進一步的改善。
第二部分將會利用銀網狀電極製備出MoO3/Ag grids/MoO3的三明治軟性電極來改善傳統的MoO3/Ag film/MoO3電極之穿透度及機械性質，並利用AFM來探討電及表面之粗糙度變化，其中MoO3作為透明電極之平整層來降低銀網狀電極之表面粗糙度，但MoO3在可見光區有明顯的衰減，我們為了改善此一現象，使用ZnO來取代MoO3並製備成ZnO/Ag grids/ZnO的透明電極，並改變銀網狀電極的厚度，發現銀網狀電極厚度會對會對ZnO的結晶產生影響，並進而影響透明電極載子遷移率。
第三部分將會探討表面處理對陽極緩衝層及銀網狀電極的影響，由於MoO3作為平整層以及陽極緩衝層，所以MoO3和電洞傳輸層(Hole Transport Layer, HTL)之間的介面特性及機制探討尤為重要，我們使用正己基磷酸 (hexylphosphonic acid, HPA)以及UV-ozone 對陽極緩衝層進行表面處理，再利用過往使用在記憶體量測活化能的變溫I-V量測方法，結合阿瑞尼士圖來計算出無機之陽極緩衝層和HTL之間的能障差距，並將使用HPA、UV-ozone處理後之MoO3陽極緩衝層製備成元件進行機制探討。
此外，在本論文中使用Ag grids/MoO3製備OLED元件，但Ag grids和MoO3平整層之間存在一明顯的能障差距，因此我們利用UV-ozone進行表面處理，使Ag grids表面形成銀氧化物(Ag2O或AgOx)的緩衝層來減少Ag grids和MoO3平整層之間的功函數差距，並利用XPS來證明銀氧化物緩衝層的組成成分，最後將其製備成OLED元件，並利用元件特性來加以驗證我們的論述。
Organic Light Emitting Diodes (OLEDs) have been developed as a future display technology due to many advantages such as fast response time, high contrast and application to be incorporated in lightweight display. Indium tin oxide (ITO) is the most commonly used material for transparent conducting electrodes (TCEs) for OLEDs due to its excellent optical transmittance (typically 85% in the visible wavelength region) and low sheet resistance (as low as 10Ω/square). However, ITO has a high cost due to the scarcity of indium and its fragility is a significant drawback for use in OLEDs. In addition, ITO requires a high processing temperature and the migration of indium limits the lifetime of OLEDs. These drawbacks limit the application of the ITO TCEs. Alternative TCEs are thus needed to replace ITO electrodes. In this research, we choose silver grids based TCEs as anode in OLEDs. The thesis are divided into three parts.
In the first part of this thesis, we fabricate the silver grids TCEs via the thermal deposition method. The proposed grid shows low sheet resistance and a good figure of merit. The sheet resistance decreased from 688 to 3.37Ω/square when the thickness was increased from 30 to 70 nm. The samples are characterized in terms of the contact angle to calculate the surface energy and polarity. The surface energy and polarity of the samples increased from 8.15 to 58.029 mJ/m2 and 0.024 to 0.067, respectively, when the sulfur content was increased from 6.67 to 9.26% (thickness increased from 50 to 70 nm). The fabricated Ag grid transparent conducting films show good optical and electrical characteristics and have potential for application in optoelectronics.
Secondly, we fabricate the MoO3/Ag grids/MoO3 (MAM) flexible TCEs to smooth the surface morphology of silver grids. The proposed structure also improves transparency compared with that of the traditional tri-layer electrode (dielectric/metal film/dielectric) by using metallic grid patterns (dielectric/metal grids/dielectric). The MoO3 layer will decrease the transmittance although it smoothes the surface roughness of the silver grids. Therefore, we replaces the MoO3 layer with zinc oxide (ZnO) to fabricate the ZnO/Ag grids/ZnO (ZAZ) structure via thermal deposition. We find the crystallization and electrical, optical, and mechanical characteristics of ZAZ TCEs are compared with those of MAM and ZnO/Ag film/ZnO TCEs. It is found that the improvement in electrical characteristics is due to the crystallization of ZnO film.
In the third part of this thesis, we discuss the surface treatment on MoO3 layer and the silver grids. When the silver grids with an UV ozone treatment duration of 15 s, the Ag2O thin films do not grow completely and current-voltage characteristics are poor. However, a 30 s UV-ozone treatment yielded good-quality Ag2O thin films. The Ag2O thin films were reconverted into the AgOx phase with further increases in UV-ozone exposure time. The Ag2O work function is nearly 5.0 eV, which decreases the injection barrier of the silver grids (~4.7 eV) and MoO3 (~5.3 eV). Nevertheless, excessive treatment time leads to the production of AgOx thin films and an increase in the work function to 5.3 eV, the same as the highest occupied molecular orbital energy of MoO3, which causes a work function mismatch. The work function mismatch between the Ag grids and the MoO3 layer results in a high injection barrier, decreasing OLED performance. The electrical properties of the electrodes and devices apparently depend on the composition of the silver oxide buffer layer, as determined using X-ray photoelectron spectroscopy. The surface and optical properties of the TCEs were also investigated. The results show that the OLED devices with the proposed TCEs have better roll off and current efficiency compared to traditional ITO-based devices. We also demonstrate the performance of OLEDs with hexylphosphonic acid (HPA) or UV-ozone treatment on their MoO3 anode buffer layers. The OLEDs with a PA treated (5 mM @1 h) MoO3 layer have lower turn-on voltage and low current efficiency roll-off under high operating current. The hole-only device (ITO/ MoO3 with PA or UV-ozone treatment/NPB/Al) was fabricated to calculate the active energy via temperature dependent I-V measurement. When the devices were operated at high temperatures, the activation energy of the UV-ozone treated, and untreated hole-only devices became nonlinear. However, the activation energy of the PA treated devices had a more stable performance at high temperatures. The interfacial resistance of the untreated hole-only devices and the PA and UV-ozone treated devices were calculated by Admittance Spectroscopy (AS).
List of Journal Paper Publications VI
Figure Captions XI
Table Captions XIV
Chapter 1 Introduction 1
1.1 General background 1
1.2 Development of Indium Free Electrodes 1
1.3 Surface treatment work on buffer layer and silver grids 2
Chapter 2 Theories and Literature Review 4
2.1 Background of OLEDs 4
2.1.1 Basic concepts of OLEDs 4
2.1.2 Basic concepts of OLEDs 5
2.2 Transparent Conductive Electrodes (TCEs) 6
2.2.1 Carrier transport of TCO/metal/TCO structure 7
2.2.2 Characteristics of Metal Grids 7
2.3 The charge injection mechanism in buffer layer 8
2.3.1 Tunneling effect 8
2.3.2 Band bending at the organic/metal interface 8
2.4 Surface treatment by phosphonic acids 9
2.4.1 Protocols for Phosphonic Acid Deposition on TCOs 10
2.4.2 Tuning the Surface Energy of TCOs：Interface Modification to Promote Adhesion and Stability 10
2.5 Figure of merit for transparent conductors 11
2.6 Zero-Field Thermionic Injection Barrier 12
2.7 Concept of Surface Energy and Contact Angle  12
2.7.1 Capillarity theory of heterogeneous nucleation 12
2.7.2 Calculation of the Surface Energy 14
2.8 Basic Concept of Haze 15
Chapter 3 Device Fabrication and Measurement 21
3.1 Flexible Transparent Conductive Electrodes (FTCEs) Fabrication 21
3.1.1 Substrate cleaning procedures 21
3.1.2 Procedures of the Silver Grids 21
3.2 Samples Prepared for Hexylphosphonic Acid Treatment 22
3.3 OLEDs Device Fabrication 23
3.4 Thermal evaporating system 23
3.5 Measuring Surface Properties of the FTCEs and buffer Layer with Different Surface Treatment. 24
3.5.1 AFM and Contact Angle 24
3.5.1 X-ray photoelectron spectroscopy analysis 25
3.5.2 Scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) analysis 25
3.6 Measurement of OLEDs characteristics 25
3.7 Ultraviolet-visible spectrophotometer measurement (UV-Visible spectrophotometer) 26
Chapter 4 Investigation of surface energy, polarity, and electrical and optical characteristics of silver grids deposited via thermal evaporation method. 31
4.1.1 Electro-optical characteristics of silver grid with different thicknesses. 31
4.1.2 Surface energy, polarity and EDS analysis of silver grids. 31
4.1.1 Conclusion 32
Chapter 5 Improvement of optical and electric characteristics of MoO3/Ag film/MoO3 flexible transparent electrode with metallic grid. 37
5.1.1 Electro-optical characteristics of bending test of the MoO3/Ag grids/MoO3 and MoO3/Ag film/MoO3. 37
5.1.2 The behavior of the MoO3/Ag grids/MoO3 and MoO3/Ag film/MoO3 during bending test. 38
5.1.3 Surface characteristics of the MoO3/Ag grids/MoO3 and MoO3/Ag film/MoO3 during bending test. 39
5.1.4 Conclusion 39
Chapter 6 Enhanced optical, electrical, and mechanical characteristics of ZnO/Ag grids/ZnO flexible transparent electrodes 52
6.1.1 Electro-optical characteristics of the ZnO/Ag grids/ZnO with different Ag thickness. 52
6.1.2 Effect of crystallite the ZnO with different thickness of Ag grids. 53
6.1.3 Mechanical feature comparison of ZAZ and MAM flexible TCEs. 54
6.1.4 Conclusion 54
Chapter 7 Improvement of OLED performance by tuning of silver oxide buffer layer composition on silver grid surface using UV-ozone treatment. 61
7.1.1 Electro-optical characteristics of the silver gridsMoO3 with different UV ozone treatment time. 61
7.1.2 Effects of UV-ozone treatment time on the silver grids surface. 61
7.1.3 Discussions of OLEDs performance and related mechanism. 62
7.1.4 Conclusion 64
Chapter 8 Effects of Buffer Layer Treatments on the Characteristics and Performances of OLEDs 75
8.1.1 Optimal parameter of hexylphosphonic acid (HPA) concentration on the Buffer Layer. 75
8.1.2 Calculation of activation energy via temperature dependent I-V measurement and comparison of OLED with different treatment methods. 76
8.1.3 Surface and interface characteristics of the buffer layer with different treatment 77
8.1.4 Conclusion 78
Chapter 9 Recommendations for Future Work 90
 X. Zhou, M. Pfeiffer, J. Blochwitz, A. Werner, A. Nollau, T. Fritz, and K. Leo, "Very-low-operating-voltage organic light-emitting diodes using AP-doped amorphous hole injection layer," Applied Physics Letters, vol. 78(4), pp. 410-412, 2001.
 H. Sasabe, H. Nakanishi, Y. Watanabe, S. Yano, M. Hirasawa, Y.J. Pu, and J. Kido, "Extremely low operating voltage green phosphorescent organic light‐emitting devices," Advanced Functional Materials, vol. 23(44), pp. 5550-5555, 2013.
 M. Fahland, P. Karlsson, and C. Charton, "Low resisitivity transparent electrodes for displays on polymer substrates," Thin Solid Films, vol. 392(2), pp. 334-337, 2001.
 S.H.K. Park, M. Ryu, C.S. Hwang, S. Yang, C. Byun, J.I. Lee, J. Shin, S.M. Yoon, H.Y. Chu, and K.I. Cho, 42.3: Transparent ZnO thin film transistor for the application of high aperture ratio bottom emission AM‐OLED display, in: SID Symposium Digest of Technical Papers, Wiley Online Library, 2008, pp. 629-632.
 A.F. Rausch, H.H. Homeier, and H. Yersin, Organometallic Pt (II) and Ir (III) triplet emitters for OLED applications and the role of spin–orbit coupling: A study based on high-resolution optical spectroscopy, in: Photophysics of Organometallics, Springer, 2010, pp. 193-235.
 M.-G. Kang, H.J. Park, S.H. Ahn, T. Xu, and L.J. Guo, "Toward low-cost, high-efficiency, and scalable organic solar cells with transparent metal electrode and improved domain morphology," IEEE Journal of Selected Topics in Quantum Electronics, vol. 16(6), pp. 1807-1820, 2010.
 L. Hung, L. Zheng, and M. Mason, "Anode modification in organic light-emitting diodes by low-frequency plasma polymerization of CHF 3," Applied physics letters, vol. 78(5), pp. 673-675, 2001.
 S.I. Na, S.S. Kim, J. Jo, and D.Y. Kim, "Efficient and flexible ITO‐free organic solar cells using highly conductive polymer anodes," Advanced Materials, vol. 20(21), pp. 4061-4067, 2008.
 H. Cho, J.-W. Shin, N.S. Cho, J. Moon, J.-H. Han, Y.-D. Kwon, S. Cho, and J.-I. Lee, "Optical effects of graphene electrodes on organic light-emitting diodes," IEEE Journal of Selected Topics in Quantum Electronics, vol. 22(1), pp. 48-53, 2016.
 D. Wang, S. Ouyang, Y. Xie, T. Tan, D. Zhu, X. Xu, and H.H. Fong, "Two photolithographic patterning schemes for PEDOT: PSS and their applications in organic light-emitting diodes," Journal of Display Technology, vol. 12(4), pp. 338-343, 2016.
 K. Lim, S. Jung, J.-K. Kim, J.-W. Kang, J.-H. Kim, S.-H. Choa, and D.-G. Kim, "Flexible PEDOT: PSS/ITO hybrid transparent conducting electrode for organic photovoltaics," Solar Energy Materials and Solar Cells, vol. 115(pp. 71-78, 2013.
 T. Dushatinski and T.M. Abdel-Fattah, "Carbon nanotube composite mesh film with tunable optoelectronic performance," ECS Journal of Solid State Science and Technology, vol. 4(5), pp. M30-M34, 2015.
 C. Guillén and J. Herrero, "Comparison study of ITO thin films deposited by sputtering at room temperature onto polymer and glass substrates," Thin solid films, vol. 480(pp. 129-132, 2005.
 K.A. Sierros, N.J. Morris, K. Ramji, and D.R. Cairns, "Stress–corrosion cracking of indium tin oxide coated polyethylene terephthalate for flexible optoelectronic devices," Thin Solid Films, vol. 517(8), pp. 2590-2595, 2009.
 G. Gustafsson, Y. Cao, G. Treacy, F. Klavetter, N. Colaneri, and A. Heeger, "Flexible light-emitting diodes made from soluble conducting polymers," Nature, vol. 357(6378), pp. 477, 1992.
 Y. Yang, Q. Huang, A.W. Metz, J. Ni, S. Jin, T.J. Marks, M.E. Madsen, A. DiVenere, and S.T. Ho, "High‐Performance Organic Light‐Emitting Diodes Using ITO Anodes Grown on Plastic by Room‐Temperature Ion‐Assisted Deposition," Advanced Materials, vol. 16(4), pp. 321-324, 2004.
 K. Saxena, V. Jain, and D.S. Mehta, "A review on the light extraction techniques in organic electroluminescent devices," Optical Materials, vol. 32(1), pp. 221-233, 2009.
 H.-W. Lu, C.-W. Huang, P.-C. Kao, and S.-Y. Chu, "ITO-free organic light-emitting diodes with MoO3/Al/MoO3 as semitransparent anode fabricated using thermal deposition method," Applied Surface Science, vol. 347(pp. 116-121, 2015.
 A.R. Gentle, S.D. Yambem, P.L. Burn, P. Meredith, and G.B. Smith, "AZO/Ag/AZO anode for resonant cavity red, blue, and yellow organic light emitting diodes," Journal of Applied Physics, vol. 119(24), pp. 245501, 2016.
 M. Girtan, "Comparison of ITO/metal/ITO and ZnO/metal/ZnO characteristics as transparent electrodes for third generation solar cells," Solar Energy Materials and Solar Cells, vol. 100(pp. 153-161, 2012.
 D.-T. Nguyen, S. Vedraine, L. Cattin, P. Torchio, M. Morsli, F. Flory, and J.C. Bernède, "Effect of the thickness of the MoO3 layers on optical properties of MoO3/Ag/MoO3 multilayer structures," Journal of Applied Physics, vol. 112(6), pp. 063505, 2012.
 B. Tian, G. Williams, D. Ban, and H. Aziz, "Transparent organic light-emitting devices using a MoO3/Ag/MoO3 cathode," Journal of Applied Physics, vol. 110(10), pp. 104507, 2011.
 X. Tian, Y. Zhang, Y. Hao, Y. Cui, W. Wang, F. Shi, H. Wang, B. Wei, and W. Huang, "Semitransparent inverted organic solar cell with improved absorption and reasonable transparency perception based on the nanopatterned MoO3/Ag/MoO3 anode," Journal of Nanophotonics, vol. 9(1), pp. 093043, 2015.
 Z. Qi, J. Cao, L. Ding, and J. Wang, "Transparent and transferrable organic optoelectronic devices based on WO3/Ag/WO3 electrodes," Applied Physics Letters, vol. 106(5), pp. 053304, 2015.
 Y. Yin, C. Lan, H. Guo, and C. Li, "Reactive Sputter Deposition of WO3/Ag/WO3 Film for Indium Tin Oxide (ITO)-Free Electrochromic Devices," ACS Applied Materials & Interfaces, vol. 8(6), pp. 3861-3867, 2016.
 C. Guillén and J. Herrero, "Transparent conductive ITO/Ag/ITO multilayer electrodes deposited by sputtering at room temperature," Optics Communications, vol. 282(4), pp. 574-578, 2009.
 J.-A. Jeong and H.-K. Kim, "Low resistance and highly transparent ITO–Ag–ITO multilayer electrode using surface plasmon resonance of Ag layer for bulk-heterojunction organic solar cells," Solar Energy Materials and Solar Cells, vol. 93(10), pp. 1801-1809, 2009.
 C. Guillén and J. Herrero, "ITO/metal/ITO multilayer structures based on Ag and Cu metal films for high-performance transparent electrodes," Solar Energy Materials and Solar Cells, vol. 92(8), pp. 938-941, 2008.
 X. Ding, J. Yan, T. Li, and L. Zhang, "Transparent conductive ITO/Cu/ITO films prepared on flexible substrates at room temperature," Applied Surface Science, vol. 258(7), pp. 3082-3085, 2012.
 H.-K. Park, J.-W. Kang, S.-I. Na, D.-Y. Kim, and H.-K. Kim, "Characteristics of indium-free GZO/Ag/GZO and AZO/Ag/AZO multilayer electrode grown by dual target DC sputtering at room temperature for low-cost organic photovoltaics," Solar Energy Materials and Solar Cells, vol. 93(11), pp. 1994-2002, 2009.
 H. Cho, C. Yun, and S. Yoo, "Multilayer transparent electrode for organic light-emitting diodes: tuning its optical characteristics," Opt. Express, vol. 18(4), pp. 3404-3414, 2010.
 H.-J. Lee, J.-W. Kang, S.-H. Hong, S.-H. Song, and S.-J. Park, "MgxZn1–xO/Ag/MgxZn1–xO Multilayers As High-Performance Transparent Conductive Electrodes," ACS Applied Materials & Interfaces, vol. 8(3), pp. 1565-1570, 2016.
 M.-G. Kang and L.J. Guo, "Semitransparent Cu electrode on a flexible substrate and its application in organic light emitting diodes," Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena, vol. 25(6), pp. 2637-2641, 2007.
 F.L.M. Sam, C.A. Mills, L.J. Rozanski, and S.R.P. Silva, "Thin film hexagonal gold grids as transparent conducting electrodes in organic light emitting diodes," Laser & Photonics Reviews, vol. 8(1), pp. 172-179, 2014.
 L. Mao, Q. Chen, Y. Li, Y. Li, J. Cai, W. Su, S. Bai, Y. Jin, C.-Q. Ma, and Z. Cui, "Flexible silver grid/PEDOT: PSS hybrid electrodes for large area inverted polymer solar cells," Nano Energy, vol. 10(pp. 259-267, 2014.
 J.J. Wang, L. Chen, X. Liu, P. Sciortino, F. Liu, F. Walters, and X. Deng, "30-nm-wide aluminum nanowire grid for ultrahigh contrast and transmittance polarizers made by UV-nanoimprint lithography," Applied physics letters, vol. 89(14), pp. 141105, 2006.
 S.M. Tadayyon, H.M. Grandin, K. Griffiths, P.R. Norton, H. Aziz, and Z.D. Popovic, "CuPc buffer layer role in OLED performance: a study of the interfacial band energies," Organic Electronics, vol. 5(4), pp. 157-166, 2004.
 H.Y. Yu, X.D. Feng, D. Grozea, Z.H. Lu, R.N.S. Sodhi, A.-M. Hor, and H. Aziz, "Surface electronic structure of plasma-treated indium tin oxides," Applied Physics Letters, vol. 78(17), pp. 2595-2597, 2001.
 H.-W. Lu, C.-W. Huang, P.-C. Kao, S.-Y. Chu, and Y.-D. Juang, "Effects of ITO Electrode Modification Using CsF Solution on Performance of Organic Light-Emitting Diodes," ECS Journal of Solid State Science and Technology, vol. 4(3), pp. R54-R59, 2015.
 M. Utsumi, N. Matsukaze, A. Kumagai, Y. Shiraishi, Y. Kawamura, and N. Furusho, "Effect of UV treatment on anode surface in organic EL displays," Thin Solid Films, vol. 363(1), pp. 13-16, 2000.
 C.-T. Wang, C.-C. Ting, P.-C. Kao, S.-R. Li, and S.-Y. Chu, "Improvement of optical and electric characteristics of MoO3/Ag film/MoO3 flexible transparent electrode with metallic grid," Journal of Applied Physics, vol. 120(19), pp. 195305, 2016.
 C.-T. Wang, C.-C. Ting, P.-C. Kao, S.-R. Li, and S.-Y. Chu, "Enhanced optical, electrical, and mechanical characteristics of ZnO/Ag grids/ZnO flexible transparent electrodes," Journal of Applied Physics, vol. 122(8), pp. 085501, 2017.
 C.W. Tang and S.A. VanSlyke, "Organic electroluminescent diodes," Applied physics letters, vol. 51(12), pp. 913-915, 1987.
 Y. Hamada, C. Adachi, T. Tsutsui, and S. Saito, "Organic electroluminescent devices with bright blue emission," OPTOELECTRON DEVICES TECHNOL., vol. 7(1), pp. 83-93, 1992.
 M. Baldo, S. Lamansky, P. Burrows, M. Thompson, and S. Forrest, "Very high-efficiency green organic light-emitting devices based on electrophosphorescence," Applied Physics Letters, vol. 75(1), pp. 4-6, 1999.
 L.J. Rothberg and A.J. Lovinger, "Status of and prospects for organic electroluminescence," Journal of Materials Research, vol. 11(12), pp. 3174-3187, 1996.
 B.G. Lewis and D.C. Paine, "Applications and processing of transparent conducting oxides," MRS bulletin, vol. 25(8), pp. 22-27, 2000.
 T. Sasabayashi, N. Ito, E. Nishimura, M. Kon, P. Song, K. Utsumi, A. Kaijo, and Y. Shigesato, "Comparative study on structure and internal stress in tin-doped indium oxide and indium-zinc oxide films deposited by rf magnetron sputtering," Thin Solid Films, vol. 445(2), pp. 219-223, 2003.
 E. Nishimura, T. Sasabayashi, N. Ito, Y. Sato, K. Utsumi, K. Yano, A. Kaijo, K. Inoue, and Y. Shigesato, "Structure and internal stress of tin-doped indium oxide and indium–zinc oxide films deposited by DC magnetron sputtering," Japanese Journal of Applied Physics, vol. 46(12R), pp. 7806, 2007.
 C.-W. Chen, P.-Y. Hsieh, H.-H. Chiang, C.-L. Lin, H.-M. Wu, and C.-C. Wu, "Top-emitting organic light-emitting devices using surface-modified Ag anode," Applied physics letters, vol. 83(25), pp. 5127-5129, 2003.
 S.Q. Hussain, W.-K. Oh, S. Kim, S. Ahn, A.H.T. Le, H. Park, Y. Lee, V.A. Dao, S. Velumani, and J. Yi, "Study of low resistivity and high work function ITO films prepared by oxygen flow rates and N2O plasma treatment for amorphous/crystalline silicon heterojunction solar cells," Journal of nanoscience and nanotechnology, vol. 14(12), pp. 9237-9241, 2014.
 M.T. Greiner, L. Chai, M.G. Helander, W.M. Tang, and Z.H. Lu, "Metal/metal‐oxide interfaces: how metal contacts affect the work function and band structure of MoO3," Advanced Functional Materials, vol. 23(2), pp. 215-226, 2013.
 F. Liu, S. Shao, X. Guo, Y. Zhao, and Z. Xie, "Efficient polymer photovoltaic cells using solution-processed MoO3 as anode buffer layer," Solar Energy Materials and Solar Cells, vol. 94(5), pp. 842-845, 2010.
 H.-J. Kim, K.-W. Seo, Y.-J. Noh, S.-I. Na, A. Sohn, D.-W. Kim, and H.-K. Kim, "Work function and interface control of amorphous IZO electrodes by MoO3 layer grading for organic solar cells," Solar Energy Materials and Solar Cells, vol. 141(pp. 194-202, 2015.
 M. Slawinski, M. Weingarten, M. Heuken, A. Vescan, and H. Kalisch, "Investigation of large-area OLED devices with various grid geometries," Organic Electronics, vol. 14(10), pp. 2387-2391, 2013.
 F.L.M. Sam, M.A. Razali, K.I. Jayawardena, C.A. Mills, L.J. Rozanski, M.J. Beliatis, and S.R.P. Silva, "Silver grid transparent conducting electrodes for organic light emitting diodes," Organic Electronics, vol. 15(12), pp. 3492-3500, 2014.
 J. Zhao, S. Zhang, X. Wang, Y. Zhan, X. Wang, G. Zhong, Z. Wang, X. Ding, W. Huang, and X. Hou, "Dual role of LiF as a hole-injection buffer in organic light-emitting diodes," Applied physics letters, vol. 84(15), pp. 2913-2915, 2004.
 T.J. Gardner, C.D. Frisbie, and M.S. Wrighton, "Systems for orthogonal self-assembly of electroactive monolayers on Au and ITO: an approach to molecular electronics," Journal of the American Chemical Society, vol. 117(26), pp. 6927-6933, 1995.
 S. Appleyard and M. Willis, "Electroluminescence: enhanced injection using ITO electrodes coated with a self assembled monolayer," Optical Materials, vol. 9(1-4), pp. 120-124, 1998.
 E.S. Gawalt, M.J. Avaltroni, N. Koch, and J. Schwartz, "Self-assembly and bonding of alkanephosphonic acids on the native oxide surface of titanium," Langmuir, vol. 17(19), pp. 5736-5738, 2001.
 E.L. Hanson, J. Schwartz, B. Nickel, N. Koch, and M.F. Danisman, "Bonding self-assembled, compact organophosphonate monolayers to the native oxide surface of silicon," Journal of the American Chemical Society, vol. 125(51), pp. 16074-16080, 2003.
 E.L. Hanson, J. Guo, N. Koch, J. Schwartz, and S.L. Bernasek, "Advanced surface modification of indium tin oxide for improved charge injection in organic devices," Journal of the American Chemical Society, vol. 127(28), pp. 10058-10062, 2005.
 S.A. Paniagua, E. Li, and S.R. Marder, "Adsorption studies of a phosphonic acid on ITO: film coverage, purity, and induced electronic structure changes," Physical Chemistry Chemical Physics, vol. 16(7), pp. 2874-2881, 2014.
 S. Wu, Calculation of interfacial tension in polymer systems, in: Journal of Polymer Science Part C: Polymer Symposia, Wiley Online Library, 1971, pp. 19-30.
 S.A. Paniagua, P.J. Hotchkiss, S.C. Jones, S.R. Marder, A. Mudalige, F.S. Marrikar, J.E. Pemberton, and N.R. Armstrong, "Phosphonic acid modification of indium− tin oxide electrodes: Combined XPS/UPS/contact angle studies," The Journal of Physical Chemistry C, vol. 112(21), pp. 7809-7817, 2008.
 J. Gantz, D. Placencia, A. Giordano, S.R. Marder, and N.R. Armstrong, "Influence of electrode surface composition and energetics on small-molecule organic solar cell performance: polar versus nonpolar donors on indium tin oxide contacts," The Journal of Physical Chemistry C, vol. 117(3), pp. 1205-1216, 2013.
 M. Timpel, M.V. Nardi, G. Ligorio, B. Wegner, M. Pätzel, B.r. Kobin, S. Hecht, and N. Koch, "Energy-level engineering at ZnO/Oligophenylene interfaces with phosphonate-based self-assembled monolayers," ACS applied materials & interfaces, vol. 7(22), pp. 11900-11907, 2015.
 M. Bender, W. Seelig, C. Daube, H. Frankenberger, B. Ocker, and J. Stollenwerk, "Dependence of film composition and thicknesses on optical and electrical properties of ITO–metal–ITO multilayers," Thin Solid Films, vol. 326(1), pp. 67-71, 1998.
 W. Gao and A. Kahn, "Controlled p doping of the hole-transport molecular material N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1′-biphenyl-4,4′-diamine with tetrafluorotetracyanoquinodimethane," Journal of Applied Physics, vol. 94(1), pp. 359-366, 2003.
 P.J. Jesuraj, K. Jeganathan, M. Navaneethan, and Y. Hayakawa, "Far-field and hole injection enhancement by noble metal nanoparticles in organic light emitting devices," Synthetic Metals, vol. 211(pp. 155-160, 2016.
 M. Ohring, Materials science of thin films, Elsevier, 2001.
 H. Fox and W. Zisman, "The spreading of liquids on low-energy surfaces. II. Modified tetrafluoroethylene polymers," Journal of Colloid Science, vol. 7(2), pp. 109-121, 1952.
 W.A. Zisman, "Influence of constitution on adhesion," Industrial & Engineering Chemistry, vol. 55(10), pp. 18-38, 1963.
 F.M. Fowkes, "Attractive forces at interfaces," Industrial & Engineering Chemistry, vol. 56(12), pp. 40-52, 1964.
 Q.-H. Wu, "Progress in modification of indium-tin oxide/organic interfaces for organic light-emitting diodes," Critical Reviews in Solid State and Materials Sciences, vol. 38(4), pp. 318-352, 2013.
 P.J. Hotchkiss, S.C. Jones, S.A. Paniagua, A. Sharma, B. Kippelen, N.R. Armstrong, and S.R. Marder, "The modification of indium tin oxide with phosphonic acids: mechanism of binding, tuning of surface properties, and potential for use in organic electronic applications," Accounts of chemical research, vol. 45(3), pp. 337-346, 2011.
 K.L. Johnson, K. Kendall, and A. Roberts, "Surface energy and the contact of elastic solids," Proc. R. Soc. Lond. A, vol. 324(1558), pp. 301-313, 1971.
 I. Yuranov, N. Dunand, L. Kiwi-Minsker, and A. Renken, "Metal grids with high-porous surface as structured catalysts: preparation, characterization and activity in propane total oxidation," Applied Catalysis B: Environmental, vol. 36(3), pp. 183-191, 2002.
 A. Eskandari, P. Sangpour, and M. Vaezi, "Hydrophilic Cu2O nanostructured thin films prepared by facile spin coating method: investigation of surface energy and roughness," Materials Chemistry and Physics, vol. 147(3), pp. 1204-1209, 2014.
 J.P. Yang, Y. Xiao, Y.H. Deng, S. Duhm, N. Ueno, S.T. Lee, Y.Q. Li, and J.X. Tang, "Electric‐Field‐Assisted Charge Generation and Separation Process in Transition Metal Oxide‐Based Interconnectors for Tandem Organic Light‐Emitting Diodes," Advanced Functional Materials, vol. 22(3), pp. 600-608, 2012.
 T.T. Trinh, N.H. Tu, H.H. Le, K.Y. Ryu, K.B. Le, K. Pillai, and J. Yi, "Improving the ethanol sensing of ZnO nano-particle thin films—the correlation between the grain size and the sensing mechanism," Sensors and Actuators B: Chemical, vol. 152(1), pp. 73-81, 2011.
 J. Alvarez-Quintana, E. Martínez, E. Pérez-Tijerina, S. Pérez-García, and J. Rodríguez-Viejo, "Temperature dependent thermal conductivity of polycrystalline ZnO films," Journal of Applied Physics, vol. 107(6), pp. 063713, 2010.
 J.-L. Wu, H.-Y. Lin, Y.-C. Chen, S.-Y. Chu, C.-C. Chang, C.-J. Wu, and Y.-D. Juang, "Effects of ZnO buffer layer on characteristics of ZnO: Ga films grown on flexible substrates: Investigation of surface energy, electrical, optical, and structural properties," ECS Journal of Solid State Science and Technology, vol. 2(4), pp. P115-P119, 2013.
 W.S. Wong and A. Salleo, Flexible electronics: materials and applications, Springer Science & Business Media, 2009.
 F.L.M. Sam, M.A. Razali, K.D.G.I. Jayawardena, C.A. Mills, L.J. Rozanski, M.J. Beliatis, and S.R.P. Silva, "Silver grid transparent conducting electrodes for organic light emitting diodes," Organic Electronics, vol. 15(12), pp. 3492-3500, 2014.
 G. Schön, J. Tummavuori, B. Lindström, C. Enzell, and C. Swahn, "ESCA studies of Ag, Ag2O and AgO," Acta Chem. Scand, vol. 27(7), pp. 24, 1973.
 V.K. Kaushik, "XPS core level spectra and Auger parameters for some silver compounds," Journal of Electron Spectroscopy and Related Phenomena, vol. 56(3), pp. 273-277, 1991.
 Y.-C. Chen, Y.-D. Juang, S.-Y. Chu, and P.-C. Kao, "Investigation of time-dependent UV-Ozone treatment on an ultra-thin AgF buffer layer for organic light-emitting diodes," Journal of The Electrochemical Society, vol. 159(4), pp. H388-H392, 2012.
 D. Cahen, A. Kahn, and E. Umbach, "Energetics of molecular interfaces," Materials Today, vol. 8(7), pp. 32-41, 2005.
 K. Banzai, S. Naka, and H. Okada, "MoO3/Ag/MoO3 anode for organic light-emitting diodes and its carrier injection property," Japanese Journal of Applied Physics, vol. 54(5), pp. 054101, 2015.
 L. Kinner, S. Nau, K. Popovic, S. Sax, I. Burgués-Ceballos, F. Hermerschmidt, A. Lange, C. Boeffel, S.A. Choulis, and E.J. List-Kratochvil, "Inkjet-printed embedded Ag-PEDOT: PSS electrodes with improved light out coupling effects for highly efficient ITO-free blue polymer light emitting diodes," Applied Physics Letters, vol. 110(10), pp. 101107, 2017.
 C. Shu-Fen, G. Xu, W. Qiang, Z. Xiao-Fei, S. Ming, and H. Wei, "Flexible white top-emitting organic light-emitting diode with a MoOx roughness improvement layer," Chinese Physics B, vol. 22(12), pp. 128506, 2013.
 Y.-F. Liu, J. Feng, Y.-F. Zhang, H.-F. Cui, D. Yin, Y.-G. Bi, J.-F. Song, Q.-D. Chen, and H.-B. Sun, "Improved efficiency of indium-tin-oxide-free organic light-emitting devices using PEDOT: PSS/graphene oxide composite anode," Organic Electronics, vol. 26(pp. 81-85, 2015.
 Y. Liu, S. Tang, and S.K. Banerjee, "Tunnel oxide thickness dependence of activation energy for retention time in SiGe quantum dot flash memory," Applied Physics Letters, vol. 88(21), pp. 213504, 2006.
 H.-J. Forman and I. Fridovich, "On the stability of bovine superoxide dismutase," J. Biol. Chem, vol. 248(pp. 2645-2649, 1973.
 M. Ishii and Y. Taga, "Influence of temperature and drive current on degradation mechanisms in organic light-emitting diodes," Applied Physics Letters, vol. 80(18), pp. 3430-3432, 2002.
 P.J. Hotchkiss, S.C. Jones, S.A. Paniagua, A. Sharma, B. Kippelen, N.R. Armstrong, and S.R. Marder, "The Modification of Indium Tin Oxide with Phosphonic Acids: Mechanism of Binding, Tuning of Surface Properties, and Potential for Use in Organic Electronic Applications," Accounts of Chemical Research, vol. 45(3), pp. 337-346, 2012.
 S.A. Paniagua, A.J. Giordano, O.N.L. Smith, S. Barlow, H. Li, N.R. Armstrong, J.E. Pemberton, J.-L. Brédas, D. Ginger, and S.R. Marder, "Phosphonic Acids for Interfacial Engineering of Transparent Conductive Oxides," Chemical Reviews, vol. 116(12), pp. 7117-7158, 2016.
 S.A. Paniagua, P.J. Hotchkiss, S.C. Jones, S.R. Marder, A. Mudalige, F.S. Marrikar, J.E. Pemberton, and N.R. Armstrong, "Phosphonic Acid Modification of Indium−Tin Oxide Electrodes: Combined XPS/UPS/Contact Angle Studies," The Journal of Physical Chemistry C, vol. 112(21), pp. 7809-7817, 2008.
 J. Cui, Q. Huang, J.C.G. Veinot, H. Yan, Q. Wang, G.R. Hutchison, A.G. Richter, G. Evmenenko, P. Dutta, and T.J. Marks, "Anode Interfacial Engineering Approaches to Enhancing Anode/Hole Transport Layer Interfacial Stability and Charge Injection Efficiency in Organic Light-Emitting Diodes," Langmuir, vol. 18(25), pp. 9958-9970, 2002.
 H.-W. Lu, C.-C. Tsai, C.-S. Hong, P.-C. Kao, Y.-D. Juang, and S.-Y. Chu, "The effects of ultra-thin cerium fluoride film as the anode buffer layer on the electrical characteristics of organic light emitting diodes," Applied Surface Science, vol. 385(pp. 139-144, 2016.