Scholarly article on topic 'Preparation and Characterization of Thin Conductive Polymer Films on the base of PEDOT:PSS by Ink-Jet Printing'

Preparation and Characterization of Thin Conductive Polymer Films on the base of PEDOT:PSS by Ink-Jet Printing Academic research paper on "Materials engineering"

CC BY-NC-ND
0
0
Share paper
Academic journal
Physics Procedia
OECD Field of science
Keywords
{"Thin film" / "Ink-jet printing" / PEDOT:PSS / "Conductive polymer" / "Transparent electrodes" / "Flexible substrate"}

Abstract of research paper on Materials engineering, author of scientific article — Nikola Perinka, Chang Hyun Kim, Marie Kaplanova, Yvan Bonnassieux

Abstract Owing to its high application potential, the printed functional layers and devices on flexible substrates attract attention of many scientists, in the last few years. Very promising area is represented by so called printed conductive polymers (polyaniline, polythiophene or polypyrroles, etc.). Currently, the most widespread conductive polymer is so called PEDOT:PSS [poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate)]. A widely used technique for the deposition of this conductive polymer is spin-coating. Since the spin-coating technique is not capable of the fine structure pattering (e.g. electrode systems for organic devices), in some cases, different techniques are strongly required (e.g. ink-jet printing). This work shows the development of the testing structure system to assess and to characterize the fine patterns of PEDOT:PSS. The testing structures were deposited on various substrates; the transparent flexible polymer foils (polyethylenterephtalate and polyethylenenaphtalene) and also on the glass substrate. The influence of the change of printing parameters, substrate and its treatment and are discussed.

Academic research paper on topic "Preparation and Characterization of Thin Conductive Polymer Films on the base of PEDOT:PSS by Ink-Jet Printing"

Available online at www.sciencedirect.com

SciVerse ScienceDirect

Physics Procedia 44 (2013) 120 - 129

10th International Conference on Solid State Chemistry, Pardubice, Czech Republic

Preparation and characterization of thin conductive polymer films on the base of PEDOT:PSS by ink-jet printing

Nikola Perinkaa*, Chang Hyun Kimb, Marie Kaplanovaa, Yvan Bonnassieuxb

aDepartment of Graphic Arts and Photophysics, Faculty of Chemical Technology, University of Pardubice, Studentska 95,

Pardubice 53210, Czech Republic bLPICM, Ecole Polytechnique, CNRS, 91128 Palaiseau, France

Abstract

Owing to its high application potential, the printed functional layers and devices on flexible substrates attract attention of many scientists, in the last few years. Very promising area is represented by so called printed conductive polymers (polyaniline, polythiophene or polypyrroles, etc.). Currently, the most widespread conductive polymer is so called PEDOT:PSS [poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate)]. A widely used technique for the deposition of this conductive polymer is spin-coating. Since the spin-coating technique is not capable of the fine structure pattering (e.g. electrode systems for organic devices), in some cases, different techniques are strongly required (e.g. ink-jet printing). This work shows the development of the testing structure system to assess and to characterize the fine patterns of PEDOT:PSS. The testing structures were deposited on various substrates; the transparent flexible polymer foils (polyethylenterephtalate and polyethylenenaphtalene) and also on the glass substrate. The influence of the change of printing parameters, substrate and its treatment and are discussed.

© 2013 The Authors. Published by Elsevier B.V.

Selection and/or peer-review under responsibility of the Organisation of the 10th International Conference on Solid State Chemistry. Keywords: thin film, ink-jet printing, PEDOT:PSS, conductive polymer, transparent electrodes, flexible substrate

1. Introduction

Nowadays, the conductive polymers on the base of polythiophene are supposed to be applied for manufacturing of flexible organic or hybrid electronic devices (e.g. transistors, displays, photovoltaic

* Corresponding author. Tel.:+420-73-127-0431 ; fax: +420-46-603-8031 . E-mail address: nikola.perinka@hotmail.com

1875-3892 © 2013 The Authors. Published by Elsevier B.V.

Selection and/or peer-review under responsibility of the Organisation of the 10th International Conference on Solid State Chemistry. doi: 10.1016/j.phpro.2013.04.016

cells, electroluminescent lamps, sensors etc.) [1-7]. Therefore, many research institutes intend to search for suitable techniques for the production of single- and multilayer systems of functional materials (e.g. based on conducting polymers) [8-10]. The main aim is also the production of large area electronics, which involves effortless, reliable, low cost and quick manufacturing technologies. The relationship between the properties of these new mentioned functional polymer materials and their chemical nature and supermolecular structure is of large importance and recently frequently studied [11-15]. For the deposition of thin layers of conducting polymers various techniques can be applied; e.g. coating [15-18], printing [19-23], laser deposition [24], spraying [25], electrospinning [26], nanolithography [27], chemical deposition [28], layer by layer [29], etc. Some of these mentioned processes provide high accuracy but do not have the capability of pattering or large area quick manufacturing. The drawback of the printing is the lower resolution in comparison to the other deposition techniques, though for some applications sufficient yet. The ink-jet printing enables low energy demands, high throughput, possibility of pattering and applicability in roll to roll processes (R2R). The current industrial ink-jet systems reach in R2R the printing speeds up to approximately 4 m/s (e.g. Impika iPress 2400). In this work, various substrates were taken and the possibility of the preparation of the fine pattern structures by means of ink-jet printing was investigated. For these purposes, a special testing structure was developed to be able to evaluate the quality and properties of the ink-jet printed lines and patterns.

2. Experimental

2.1. Testing structure

The main scope of the present work is the preparation of the fine lines for the later fabrication of the conductive transparent electrodes. For the experiments, two testing structures were created to be able to test the resolution and the quality of the prepared printed patterns. The Testing structure is shown in Fig. 1. The testing structure in Fig. 1 was developed to test the quality and the resolution of the print. The substructure number 1 in Fig. 1 (the two squares in the corners of the Testing structure) is related to the testing of the capability of the printer to print the full print areas objects. The width of the thinnest printable line was tested by means of the substructure 2 in both directions and the nominal width was modulated from 20 to 100 ^m (with the step of 20 ^m). The substructure 3 in Fig. 1 was designed to test the achievable space resolution between the two adjacent lines of the nominal width 200 ^m and the length 1000 ^m, which were oriented in the print direction (direction parallel to the movement of the printhead). The spacing between two lines was modulated from 200 to 20 ^m, with the step of 20 ^m (10 small double line structures, where each had different spacing between the two lines; this substructure was repeated twice in the testing structure layout to assess the repeatability of the print within the Testing structure). The same system of the structure was used in the case of the substructure 4, with the difference that both lines were orientated in the perpendicular direction to print. To be able to test the electrical parameters of the PEDOT:PSS prints, in the middle of the Testing structure in the Fig. 1, one line with the nominal width of 200 ^m and length 7 mm was positioned (substructure 5). After the print, the substrate with the printed structure was supposed to be obtained by gold (or aluminum) 4-point probe contacts, to test the conductivity of the PEDOT:PSS prints (shadow substructure 6 in the Fig 1).

Fig. 1. Testing structure for inkjet-printed PEDOT:PSS films in this study

2.2. Materials

The PEDOT:PSS (1.3 to 1.7% by weight in water) was applied in a form of the conductive dispersion Clevios™ P VP AI 4083 (from the producer Heraeus). This dispersion is used especially in organic photovoltaics for the fabrication of transparent buffer layer and it is usually applied by means of spin coating technique. The printing was carried out on three different kinds of plastic polymer substrates; Melinex® ST 504 (polyethylenterephtalate, i.e. PET), Teonex® Q83 (polyethylenenaphtalene, i.e. PEN), Indium tin oxide (ITO) coated PET foil (Sigma Aldrich, (639303-5EA), 60 Q/sq) and glass substrates. Before the printing, the polymer foils were cleaned in ultrasonic bath of isopropyl alcohol (IPA) solution for 15 min. To improve the wetting of the polymer foils, some of them were later also additionally treated by means in an UV/O3 chamber on Novascan PSD Series Digital Ozone System for 15 min. The influence of the treatment will be discussed in the next section.

2.3. Printing

For the printing, the laboratory ink-jet device Dimatix DMP-2831 was applied. The printing settings were first optimized according to the tests and producer's specifications. The drop spacing was set to the value of 20 ^m and no heating for printhead (i.e. the ink) was applied (28 °C). The used printheads dispose of 16 nozzles. However, it should be noted that due to the clogging effects, during the realization of the experiment, some of the nozzles stopped to work, which results in different speed of the printing. During the printing process, we systematically controlled three main parameters:

• Printhead volume (1 pl and 10 pl printheads)

• Temperature of the substrate (25, 40 and 60 °C)

• Firing voltage (20, 30 and 40 V)

Before the printing, the conductive dispersion inks were filtered using the 0.45 ^m filter. After the printing, the samples were dried under ambient atmosphere without any additional heat treatment. The quality of the printed lines was investigated also in the interdependence on the orientation of the printed objects. Two orientations were distinguished during the printing experiments; the print direction (parallel to the movement of the printhead) and the perpendicular direction (perpendicular to the movement of the printhead).

2.4. Printed layer characterization

The influence of the named parameters was studied by means of the optical microscopy (optical microscope Leica DM4000 M and camera system Leica DFC295) and the four point probe camera vision system. The thickness and morphology of the prepared PEDOT:PSS layers was studied by means of the mechanical stylus profiler Veeco Dektak 150. The electrical characterization was realized by means of the two-point and four-point probe measuring bridge. The electrical measurements were carried out by means of the contacting of high vacuum evaporated Gold contacts (see shadow line substructure 6 in Fig. 1).

3. Results and discussion

3.1. Printing conditions and parameters

First, the influence of the printhead volume was investigated. During the printing experiments, it was found out that the printhead with the volume of 1 pl provides the lines with of higher quality, in comparison to 10 pl head, in terms of resolution and edge sharpness. However, using the 1 pl printhead, some defects were observed (e.g. "stacked coins" [30]), which can be seen substructure 2 (see Fig. 1) in Fig. 2. The 10 pl printhead, on the other side provides the structures of higher thickness of the printed layer. To increase the layer thickness during the utilization of 1 pl printheads, more layers were deposited on each other. In this case, problems with the accurate registration of the individual layers were noted.

Fig. 2. Formation of the "stacked coins" (horizontal lines in the micrograph) on the line in the perpendicular direction (upper scale of micrographs 500 ^m; substrate Melinex® ST 504; firing voltage 40 V; substrate temperature 25 °C)

The temperature of the substrate showed a significant influence on the resulting morphology of the prepared layers. When higher temperatures are applied on the substrate, the PEDOT:PSS layers tend to form bubbles in its structure and also to burst (Fig. 3), which was observed in substructure 1 (see Fig. 1). The resulting homogeneity the printed layer is therefore also very low. Another observed effect is the fact due to the higher evaporation rate by increased temperature, the deposited layer of PEDOT:PSS gets dried very quickly and therefore sometimes the new fired droplets already fall on the layer of the dried material, which prevents the mutual flow connection of the two droplets.

Fig. 3. Micrographs illustrating the comparison of the layer morphology of two layers printed at two different temperatures (upper scale of micrographs 300 ^m; substrate Melinex® ST 504; firing voltage 30 V): (a) t = 25 °C; (b) t = 60 °C

When changing the firing voltage applied in the printhead, the quantity of the deposited material could be controlled. Higher firing voltage leads to the formation of stronger acoustic pulses in the printhead and finally also to the deposition of more polymer and formation of higher thickness of the printed layer. Also lower spreading of the wet deposited material occurs when lower firing voltage is applied.

During the printing experiments, it became obvious that the orientation of the printed patterns has a significant impact on the resulting quality as well (morphology and the shape and sharpness of the edges of the printed lines of substructure 2, see Fig. 4).

Fig.4. Micrographs illustrating the comparison of the layer morphology and edge sharpness in the interdependence of the direction of the printing (upper scale of micrographs 300 ^m): (a) print direction; (b) perpendicular direction

3.2. Substrate conditions

The substrate treatment prior to the printing process had a substantial impact on the wettability of the ink on the substrate. After the treatment of the substrate by means of the UV/O3 irradiation chamber system, significant improvement of the ink spreading on the substrate was observed on lines in the substructure 5 of the Testing structure, see Fig. 5. The reason lies in the increasing of the roughness of the substrate of the polymer [31]. Before the UV/O3 treatment, the deposited ink tends to form on the substrate rather discrete drops, whereas after the treatment continuous structures were formed.

Fig.5. Micrographs illustrating the influence of the substrate treatment by means of UV/O3 irradiation (upper scale of micrographs 300 ^m; substrate Melinex® ST 504): (a) no treatment; (b) with the treatment

When various kinds of substrate were applied (polymer, metal oxide and glass), differences in the formation of the conductive layer and the final morphology were observed, as shown in Fig. 6 (patterns in the substructure 3 of the Testing structure in Fig. 1). The thin-film interference on PEDOT:PSS layer in Fig. 6 indicates the changes in the thickness within the printed patterns. The smoothest layer morphology was observed on the glass substrate, nevertheless with the lowest layer thickness. On the PET foil, the homogeneity of the layers was lower compared to the glass substrate sample. Also the differences in the edge sharpness can be observed. When printed on the PEN foil, the ink tends to spread too much on the substrate, which then subsequently leads to the interconnection of the printed patterns. In the case of ITO/PET foil, the PEDOT:PSS did not spread completely on the area of the ITO surface. The differences in the ink spreading behavior on the different substrates could be attributed to different surface roughness and surface energy of each examined substrate.

a) Ml b) "(mS/KKl

- SORB

Fig. 6. Micrographs illustrating the comparison of layer morphology of the PEDOT:PSS on different substrates (upper scale of micrographs 300 ^m for (a) to (c) and 200 ^m for (d)): (a) ITO/PET; (b) PEN; (c) PET; (d) glass substrate

3.3. Printing resolution

The achieved width of the thinnest printable line of PEDOT:PSS was approximately 40 |m. The smallest printable distance between two lines was resolved up to 50 |m, which corresponds to the distance of 100 |m (in the nominal value) in the Testing structure (substructure 3, Fig. 1). The maximal printing resolution depends also on the orientation of the printed patterns on the Testing structure and the change of the pattern dimensions due to the ink spreading on the substrate. The change of the printed line width in comparison to the Testing structure (nominal line width) is indicated in Fig. 7. In general, better quality of the printed lines and higher printing resolution was revealed in the print direction.

j! 200 v !=

>5 50 0

0 50 100

Nominal line width [|im]

O Print direction

□ Perpendicular O

direction ^

Fig. 7. Change of the width of printed line of PEDOT:PSS in comparison to the nominal line width on Testing structure

3.4. Thickness of the printed layers

Based on the measurements carried out by means of the profiler, the thickness of the layers ranged approximately from 80 nm to 750 nm. The thickness of the layers prepared by means of 1 pl and 10 pl printheads was significantly different. By applying the 10 pl printhead, the thicknesses in the range from 400 to 750 nm were observed, whereas by using the 1 pl printhead the thicknesses ranged only from 80 to 200 nm. When using the 1 pl printheads, in order to achieve the same thicknesses as in the case of 10 pl printheads, two or three layers needed to be deposited on each other. The measured profiles of the printed lines (substructure 5 of Testing structure in Fig. 1) are compared in Fig. 8.

1000 200

800 - 0 150

/ S 100

400 - \ <D Jâ

200 \ o JS 50

1 \ E-

0 •fin. 1 , , , \ . 0

400 x [|m] (a)

350 x [|m] (b)

Fig. 8. Comparison of the printed lines cross-sectional profiles for two different printhead volumes (substrate Melinex® ST 504): (a) 10 pl printhead; (b) 1 pl printhead

3.5. Electrical characterization

The electrical measurements on the printed line of PEDOT:PSS showed the resistance of 200 Mfi (two-point probe) and 600 Mfi (four-point probe). The resistance estimated by means of the four-point probe corresponds to the conductivity of 1.1 mS/cm (by the average thickness of 600 nm, the line width 250 ^m and the contact distance 1000 ^m), which is in good agreement with the producer's specifications.

4. Conclusion

In this work, we showed that the PEDOT:PSS based dispersion for spin-coating can be successfully applied to the ink-jet printing technique and therefore patterned as well. Furthermore, the system of testing and characterizing of the ink-jet printed layers was demonstrated. The thickness and morphology of the printed PEDOT:PSS layers can be controlled by means of the printhead volume, firing voltage and temperature of the substrate. The deposition of the layers can be realized on various flexible substrates, such as PET or PEN foils. The morphology of the layers was substantially influenced by the substrate material characteristics. The thickness of the prepared layers ranged from 80 to 750 nm. The lines of the width up to 40 ^m could were observed. It was noticed that the treatment by means of UV/O3 irradiation of the substrate improves the wetting and the printability of the ink distinctively. Further printing experiments and detailed characterization of printing conditions are planned.

Acknowledgements

The authors thank to grant project CZ.1.07/2.3.00/09.0104 "Education and Development of Research Team for Centre of Material Science Pardubice" realized by European Structural Funds and Ministry of Education, Youth and Sports of The Czech Republic within The Education for Competitiveness Operational Programme (ECOP). Other thanks belong to the Chemnitz University of Technology for the cooperation during the evaluation of the experiments. C. H. Kim thanks to the Vice Presidency for External Relations (DRE) in Ecole Polytechnique for the Ph.D. fellowship.

References

[1] Elschner A. 2011; PEDOT: Principles and applications of an intrinsically conductive polymer. Boca Raton, FL: CRC Press.

[2] Kirchmeyer S, Reuter K. Scientific importance, properties and growing applications of poly(3,4-ethylenedioxythiophene). J. Mater. Chem. 2005;15:2077-2088.

[3] Lim JA, Cho JH, Park YD, Kim DH, Hwang M, Cho K. Solvent effect of inkjet printed source/drain electrodes on electrical properties of polymer thin-film transistors. Appl. Phys. Lett. 2006;88:082102.

[4] Mannerbro R, Ranlöf M, Robinson N, Forchheimer R. Inkjet printed electrochemical organic electronics, Synth. Met. 2008;158:556-560.

[5] Aernouts T, Vanlaeke P, Geens W, Poortmans J, Heremans P, Borghs S, Mertens R, Andriessen R, Leenders L. Printable anodes for flexible organic solar cell modules. Thin Solid Films 2004;451-452:22-25.

[6] Kim JY, Lee K, Coates NE, Moses D, Nguyen TQ, Dante M, Heeger AJ. Efficient tandem polymer solar cells fabricated by all-solution processing. Science 2007;317:222-225.

[7] Tarver J, Yoo JE, Loo YL. 4.14 - Organic Electronic Devices with Water-Dispersible Conducting Polymers. Comprehensive

Nanoscience and Technology 2011;4:413-446.

[8] Jayaraman S, Rajarathnam D, Srinivasan MP, Formation of polythiophene multilayers on solid surfaces by covalent molecular assembly. Materials Science and Engineering: B 2010;168:45-54.

[9] Aradilla D, Estrany F, Oliver R, Alemán R, Properties of nanometric and micrometric multilayered films made of three conducting polymers. European Polymer Journal 2010;46: 2222-2228.

[10] Jarkov A, Bereznev S, Laes K, Volobujeva O, Traksmaa R, Opik A, Mellikov E, Conductive polymer PEDOT:PSS back contact for CdTe solar cell. Thin Solid Films 2011;519: 7449-7452.

[11] Bailo D, Generosi A, Albertini RV, Caminiti R, De Bettignies R, Paci B. Time-resolved morphological study of 'PEDOT:PSS' hole transporting layer for polymer solar cells. Synthetic Metals 2012;162:808-812.

[12] Wilson P, Lekakou C, Watts JF. A comparative assessment of surface microstructure and electrical conductivity dependence on co-solvent addition in spin coated and inkjet printed poly(3,4-ethylenedioxythiophene):polystyrene sulphonate (PEDOT:PSS). Organic Electronics 2012;13:409-418.

[13] Friedel B, Brenner TJK, McNeill CR, Steiner U, Greenham NC. Influence of solution heating on the properties of PEDOT:PSS colloidal solutions and impact on the device performance of polymer solar cells. Organic Electronics 2011;12:1736-

[14] King ZA, Shaw CM, Spanninga SA, Martin DC. Structural, chemical and electrochemical characterization of poly(3,4-Ethylenedioxythiophene) (PEDOT) prepared with various counter-ions and heat treatments. Polymer 2011;52:1302-1308.

[15] Scott A. Mauger, Lilian Chang, Christopher W. Rochester, Adam J. Moulé, Directional dependence of electron blocking in PEDOT:PSS. Organic Electronics 2012;13:2747-2756.

[16] Ladhe RD, Gurav KV, Pawar SM, Kim JH, Sankapal BR. p-PEDOT:PSS as a heterojunction partner with n-ZnO for detection of LPG at room temperature. Journal of Alloys and Compounds 2012;515:80-85.

[17] Kawahara J, Ersman PA, Engquist I, Berggren M. Improving the color switch contrast in PEDOT:PSS-based electrochromic display. Organic Electronics 2012:13:469-474.

[18] Ely F, Avellaneda CO, Paredez P, Nogueira VC, Santos TEA, Mammana VP, Molina C, Brug J, Gibson G, Zhao L. Patterning quality control of inkjet printed PEDOT:PSS films by wetting properties. Synthetic Metals 2011;161:2129-2134.

[19] Youn H, Jeon K, Shin S, Yang M, All-solution blade-slit coated polymer light-emitting diodes. Organic Electronics 2012;13:1470-1478.

[20] Xiong Z, Liu C. Optimization of inkjet printed PEDOT:PSS thin films through annealing processes. Organic Electronics 2012;13:1532-1540.

[21] Schrodner M, Sensfuss S, Schache H, Schultheis K, Welzel T, Heinemann K, Milker R, Marten J, Blankenburg L, Reel-to-reel wet coating by variation of solvents and compounds of photoactive inks for polymer solar cell production. Solar Energy Materials and Solar Cells 2012;107:283-291.

[22] Basiricô L, Cosseddu P, Fraboni B, Bonfiglio A. Inkjet printing of transparent, flexible, organic transistors. Thin Solid Films 2011;520:1291-1294.

[23] Cho C-K, Hwang W-J, Eun K, Choa S-H, Na S-I, Kim H-K. Mechanical flexibility of transparent PEDOT:PSS electrodes prepared by gravure printing for flexible organic solar cells. Solar Energy Materials and Solar Cells 2011;95: 3269-3275.

[24] Johnson SL, Park HK, Haglund Jr RF, Properties of conductive polymer films deposited by infrared laser ablation. Applied Surface Science 2007;253: 6430-6434.

[25] Kim Y, Lee J, Kang H, Kim G, Kim N, Lee K. Controlled electro-spray deposition of highly conductive PEDOT:PSS films. Solar Energy Materials and Solar Cells 2012;98:39-45.

[26] Carrasquillo KV, Pinto NJ. Tunable Schottky diodes fabricated from crossed electrospun SnO2/PEDOT-PSSA nanoribbons. Materials Science and Engineering: B 2012;177: 805-809.

[27] Lu H-H, Lin C-Y, Hsiao T-C, Fang Y-Y, Ho K-C, Yang D, Lee C-K, Hsu S-M, Lin C-W. Electrical properties of single and multiple poly(3,4-ethylenedioxythiophene) nanowires for sensing nitric oxide gas. Analytica Chimica Acta 2009;640:68-74.

[28] Ladhe RD, Gurav KV, Pawar SM, Kim JH, Sankapal BR. p-PEDOT:PSS as a heterojunction partner with n-ZnO for detection of LPG at room temperature. Journal of Alloys and Compounds 2012;515:80-85.

[29] Wakizaka D, Fushimi T, Ohkita H, Ito S. Hole transport in conducting ultrathin films of PEDOT/PSS prepared by layer-by-layer deposition technique. Polymer 2004;45: 8561-8565.

[30] Soltman D, Subramanian V. Inkjet-Printed Line Morphologies and Temperature Control of the Coffee Ring Effect. Langmuir 2008;24:2224-2231.

[31] Jang J, Jeong Y. Nano roughening of PET and PTT fabrics via continuous UV/O3 irradiation. Dyes and Pigments 2006;69:137-143.