Abstract
For flexible electronic devices, the transparent conductive electrode (TCE) is the most important material for determining the flexibility of devices. Due to the brittleness of the indium tin oxide (ITO) electrode, several alternative TCEs have been developed. However, it is still difficult to successfully achieve quality as good as ITO. In this study, the flexibility of the ITO electrode was investigated with strain and fracture analysis. Effects of thickness of the ITO and the substrate on the flexibility of ITO were investigated by bending tests, numerical simulation and theoretical analysis. Flexibility of ITO electrode can be increased by reducing the thickness of ITO and substrate material. An ITO electrode with a substrate less than 50 μm could be bent to less than 4 mm without failure, and used in flexible electronics. Effects of different substrate materials on the flexibility of ITO were also investigated based on fracture analysis. We investigated the effects of PEDOT [poly(3,4-ethylenedioxythiophene)] as a buffer layer to improve flexibility. Higher flexibility of the ITO/PEDOT hybrid electrode compared to ITO was attributed to the PEDOT layer, which smoothened ITO surface and decreased the density of pinholes or voids of ITO, resulting in higher crack resistance.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Ajuria J, Ugarte I, Cambarau W, Etxebarria I, Tena-Zaera R, Pacios R (2012) Insights on the working principles of flexible and efficient ITO-free organic solar cells based on solution processed Ag nanowire electrodes. Sol Energy Mater Sol Cells 102:148–152. doi:10.1016/j.solmat.2012.03.009
Bae S, Kim H, Lee Y, Xu XF, Park JS, Zheng Y, Balakrishnan J, Lei T, Kim HR, Song YI, Kim YJ, Kim KS, Ozyilmaz B, Ahn JH, Hong BH, Iijima S (2010) Roll-to-roll production of 30-inch graphene films for transparent electrodes. Nat Nanotechnol 5:574–578. doi:10.1038/nnano.2010.132
Beuth JL Jr (1992) Cracking of thin bonded films in residual tension. Int J Solids Struct 29:1657. doi:10.1016/0020-7683(92)90015-L
Cairns DR, Witte RP II, Sparacin DK, Sachsman SM, Paine DC, Crawford GP, Newton RR (2000) Strain-dependent electrical resistance of tin-doped indium oxide on polymer substrates. Appl Phys Lett 76:1425–1427. doi:10.1063/1.126052
Chen Z, Cotterell B, Wang W (2002) The fracture of brittle thin films on compliant substrates in flexible displays. Eng Fract Mech 69:597–603. doi:10.1016/S0013-7944(01)00104-7
Cook RF, Liniger EG (1999) Stress-corrosion cracking of low-dielectric-constant spin-on-glass thin films. J Electrochem Soc 146:4439–4448. doi:10.1149/1.1392656
Crawford GP (2005) Flexible flat panel displays. Wiley, England. doi:10.1002/0470870508
Dundurs J (1969) Edge-bonded dissimilar orthogonal elastic wedges under normal and shear loading. J Appl Mech 36:460–466. doi:10.1115/1.3601236
Garnett EC, Cai W, Cha JJ, Mahmood F, Connor ST, Christoforo MG, Cui Y, McGehee MD, Brongersma ML (2012) Self-limited plasmonic welding of silver nanowire junctions. Nat Mater 11:241–249. doi:10.1038/nmat3238
Hu LB, Hecht DS, Gruner G (2010) Carbon nanotube thin films: fabrication, properties, and applications. Chem Rev 110:5790–5844. doi:10.1021/cr9002962
Hu L, Wu H, Cui Y (2011) Metal nanogrids, nanowires, and nanofibers for transparent electrodes. MRS Bull 36:760–765. doi:10.1557/mrs.2011.234
Kang MG, Xu T, Park HJ, Luo X, Guo LJ (2010) Efficiency enhancement of organic solar cells using transparent plasmonic Ag nanowire electrodes. Adv Mater 22:4378–4383. doi:10.1002/adma.201001395
Lee S, Kwon JY, Yoon D, Cho H, You J, Kang YT, Choi D, Hwang W (2012) Bendability optimization of flexible optical nanoelectronics via neutral axis engineering. Nanoscale Res Lett 7:256–262. doi:10.1186/1556-276X-7-256
Leem DS, Edwards A, Faist M, Nelson J, Bradley DDC, Mello JC (2011) Efficient organic solar cells with solution-processed silver nanowire electrodes. Adv Mater 23:4371–4375. doi:10.1002/adma.201100871
Leterrier Y, Medico L, Demarco F, Manson J, Betz U, Escola M, Olsson M, Atamny F (2004) Mechanical integrity of transparent conductive oxide films for flexible polymer-based displays. Thin Solid Films 460:156–166. doi:10.1016/j.tsf.2004.01.052
Lewis J (2006) Material challenge for flexible organic devices. Mater Today 9:38–45. doi:10.1016/S1369-7021(06)71446-8
Lim K, Jung S, Kim JK, Kang JW, Kim JH, Choa SH, Kim DG (2013) Flexible PEDOT:PSS/ITO hybrid transparent conducting electrode for organic photovoltaics. Sol Energ Mat Sol 115:71–78. doi:10.1016/j.solmat.2013.03.028
Liu XH, Lane MW, Shaw TM, Liniger EG, Rosenberg RR, Edelstein DC (2004) Low-k BEOL mechanical modeling. In: Proceedings of advanced metallization conference, pp 361–367
Liu XH, Lane MW, Shaw TM, Simonyi E (2007) Delamination in patterned films. Int J Solids Struct 44:1706–1718. doi:10.1016/j.ijsolstr.2006.07.023
Medford AJ, Lillieda MR, Jørgensen M, Aarø D, Pakalski H, Fyenbo J, Krebs FC (2010) Grid-connected polymer solar panels: initial considerations of cost, lifetime, and practicality. Opt Express 18:A272–A285. doi:10.1364/OE.18.00A272
Mei H, Pang Y, Huang R (2007) Influence of interfacial delamination on channel cracking of elastic thin films. Int J Fract 148:331–342. doi:10.1007/s10704-008-9205-7
Na SI, Kim SS, Jo J, Kim DY (2008) Efficient and flexible ITO-free organic solar cells using highly conductive polymer anodes. Adv Mater 20:4061–4067. doi:10.1002/adma.200800338
Park SI, Ahn JH, Feng X, Wang S, Huang Y, Rogers JA (2008) Theoretical and experimental studies of bending of inorganic electronic materials on plastic substrates. Adv Funct Mater 18:2673–2684. doi:10.1002/adfm.200800306
Park J, Lee J, Noh YY (2012) Optical and thermal properties of large-area OLED lightings with metallic grids. Org Electron 13:184–194. doi:10.1016/j.orgel.2011.10.024
Peng C, Jia Z, Neilson H, Li T, Lou J (2013) In situ electro-mechanical experiments and mechanics modeling of fracture in indium tin oxide-based multilayer electrodes. Adv Eng Mater 15:250–256. doi:10.1002/adem.201200169
Seo TH, Oh TS, Chae SJ, Park AH, Lee KJ, Lee YH, Suh EK (2011) Enhanced light output power of GaN light-emitting diodes with graphene film as a transparent conducting electrode. Jpn J Appl Phys 50:125103. doi:10.1143/JJAP.50.125103
Sim B, Kim EH, Park J, Lee M (2009) Highly enhanced mechanical stability of indium tin oxide film with a thin Al buffer layer deposited on plastic substrate. Surf Coat Technol 204:309–312. doi:10.1016/j.surfcoat.2009.07.028
Suga T, Elssner E, Schmander S (1988) Composite parameters and mechanical compatibility of material joints. J Comp Mater 22:917–934. doi:10.1177/002199838802201002
Suo Z, Ma EY, Gleskova H, Wagner S (1999) Mechanics of rollable and foldable film-on-foil electronics. Appl Phys Lett 74:1177–1179. doi:10.1063/1.123478
Tang CW (1986) Two layer organic photovoltaic cell. Appl Phys Lett 48:183–185. doi:10.1063/1.96937
Trottier CM, Glatkowski P, Wallis P, Luo J (2005) Properties and characterization of carbon-nanotube-based transparent conductive coating. J Soc Inf Disp 13:759–763. doi:10.1889/1.2080514
Tsui TY, McKerrow AJ, Vlassak JJ (2007) The effect of water diffusion on the adhesion of organosilicate glass film stacks. J Mech Phys Solids 54:887–908. doi:10.1016/j.jmps.2005.12.004
Vlassak JJ (2003) Channel cracking in thin films on substrates of finite thickness. Int J Fract 119:299–323. doi:10.1023/A:1024962825938
Wang SH, Hsiao YJ, Fang TH, Chen SL, Kang SH (2014) Effects of ITO film annealing temperature on hybrid solar cell performance. Microsyst Technol 20:1181–1185. doi:10.1007/s00542-013-1910-0
Wassei JK, Kaner RB (2010) Graphene, a promising transparent conductor. Mater Today 13:52–59. doi:10.1016/S1369-7021(10)70034-1
Wong WS, Salleo A (2009) Flexible electronics: material and application. Springer, New York
Yeh MK, Chang LY, Lu MR, Cheng HC, Wang PH (2014) Bending stress analysis of flexible touch panel. Microsyst Technol 20:1641–1646. doi:10.1007/s00542-014-2200-1
Yip HL, Hau SK, Baek NS, Jen AKY (2008) Self-assembled monolayer modified ZnO/metal bilayer cathodes for polymer/fullerene bulk-heterojunction solar cells. Appl Phys Lett 92:193313-1–193313-3. doi:10.1063/1.2919524
Acknowledgments
This study was supported by a Grant from the R&D Program, “Database for mechanical properties and flexibility of flexible transparent electrode” which are funded by Korea Research Institute of Chemical Technology.
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Jung, H.S., Eun, K., Kim, Y.T. et al. Experimental and numerical investigation of flexibility of ITO electrode for application in flexible electronic devices. Microsyst Technol 23, 1961–1970 (2017). https://doi.org/10.1007/s00542-016-2959-3
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s00542-016-2959-3