Organic Electronics 15 (2014) 1849–1855

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The enhancement of electrical and optical properties of PEDOT:PSS using one-step dynamic etching for flexible application Kyounga Lim a, Sunghoon Jung a, Seunghun Lee a, Jinhee Heo b, Juyun Park c, Jae-Wook Kang d, Yong-Cheol Kang c,⇑, Do-Geun Kim a,⇑ a

Plasma Coating Research Group, Korea Institute of Materials Science (KIMS), 797, Changwondaero, Changwon, Gyeongnam 641-831, Republic of Korea Advanced Characterization & Analysis Research Group, Korea Institute of Materials Science (KIMS), 797, Changwondaero, Changwon, Gyeongnam 641-831, Republic of Korea c Department of Chemistry, Pukyong National University, 45, Yongso-ro, Nam-Gu, Busan 608-737, Republic of Korea d Department of Flexible and Printable Electronics, Chonbuk National University, 567, Baekje-Daero, Deokjin-Gu, Jeonju 561-756, Republic of Korea b

a r t i c l e

i n f o

Article history: Received 5 November 2013 Received in revised form 30 March 2014 Accepted 9 April 2014 Available online 10 May 2014 Keywords: Dynamic etching Conductivity enhancement PEDOT:PSS Flexible device

a b s t r a c t The conductivity enhancement of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) by dynamic etching process was investigated to introduce the outstanding and simplest method for soft electronics. Four different samples which were pristine PEDOT:PSS, PEDOT:PSS doped with 5 wt.% DMSO, PEDOT:PSS with dipping process, and PEDOT:PSS with dynamic etching process were prepared to compare the properties such as conductivity, morphology, relative atomic percentage, and topography. All samples were characterized by four point probe, current atomic force microscopy (C-AFM), X-ray photoelectron spectroscopy (XPS), and UV–visible spectroscopy. The conductivity of the sample with dynamic etching process showed the highest value as 1299 S/cm among four samples. We proved that the dynamic etching process is superior to remove PSS phase from PEDOT:PSS film, to flow strong current through entire surface of PEDOT:PSS, and to show the smoothest surface (RMS 2.28 nm). XPS analysis was conducted for accurate chemical and structural surface environments of four samples and the relative atomic percentage of PEDOT in the sample with dynamic etching was the highest as 29.5%. The device performance of the sample with the dynamic etching process was outstanding as 10.31 mA/cm2 of Jsc, 0.75 eV of Voc, 0.46 of FF, and 3.53% of PCE. All properties and the device performance for PEDOT:PSS film by dynamic etching process were the most excellent among the samples. Ó 2014 Elsevier B.V. All rights reserved.

1. Introduction In the late 20th century, performances of organic optoelectronic devices have rapidly progressed thereby the ⇑ Corresponding authors. Tel.: +82 51 629 5585; fax: +82 51 629 5584 (Y.C. Kang). Tel.: +82 55 280 3507; fax: +82 55 280 3570 (D.-G. Kim). E-mail addresses: [email protected] (Y.-C. Kang), dogeunkim@kims. re.kr (D.-G. Kim). http://dx.doi.org/10.1016/j.orgel.2014.04.014 1566-1199/Ó 2014 Elsevier B.V. All rights reserved.

demand for flexible devices has intensively been on the rise these days. Indium tin oxide (ITO) is the most popular material as a transparent conductive electrode for optoelectronic devices because ITO has great electrical and optical properties. For flexible devices, ITO, however, has a crucial weak point in the aspect of mechanical property because ITO is easily cracked under internal and external force [1–4]. Therefore many scientists have proposed lots of materials to overcome ITO’s disadvantage such as

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graphenes [5], carbon nanotubes [6], metal nanowires [7–10], and conductive polymers [11–13]. There, however, have the points at issues in those materials. The process to obtain graphenes with a good quality is very complicated [14], carbon nanotubes have relatively high resistance [15], and metal nanowires have some problems to control their morphology and interconnection between nanowires [8,16]. Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), one of conductive polymers, is a very attractive candidate for flexible optoelectronic devices because PEDOT:PSS has excellent transparency in the visible region, good conductivity with some treatments, and excellent flexibility. Originally, PEDOT is not soluble in most solvents so poly(styrenesulfonate) (PSS) has to be doped into PEDOT as a counter ion for better solubility. But doped PSS leads to dramatic decrease of conductivity because of its insulating property. In order to improve the conductivity of PEDOT:PSS, there have been a lot of experimental reports [19–31]. In the early stage, the researches for PEDOT:PSS have investigated the structural constituents of PEDOT:PSS [17,18]. Recently, researchers have focused to find new methods to improve PEDOT:PSS conductivity. One of well-known methods is addition of secondary doping solvents such as sorbitol [19–21], (poly)-ethylene glycol, alcohols (with more than two hydroxyl groups) [22–24], dimethyl sulfoxide (DMSO) [25–27], and N,N-dimethylformamide [28]. Another method is called as ‘dipping process’ [29–31]. Kim et al. introduced ‘dipping process’ and they obtained over 1300 S/cm of the conductivity with this method [29]. Na et al. also reported two-step method which is vaporizing process or dropping process followed by dipping process and they obtained over 1400 S/cm of the conductivity for PEDOT:PSS [30,31]. There are two main interpretations for the conductivity enhancement of PEDOT:PSS. The first is the mechanisms by adding additives, which include the theories: (1) conformational changes of PEDOT chains from benzonoid structure to quinoid structure [24,32], (2) a screen effect by inserting additives between PEDOT and PSS [25]. The second is the mechanism by dipping process. This mechanism is dissolving only PSS phase into an additive solvent and removing PSS phase from the surface of PEDOT:PSS film. Among two mechanisms, the latter is much more effective to raise the conductivity of PEDOT:PSS. Even though the dipping process achieves higher conductivity, this process should proceed two steps to improve PEDOT:PSS conductivity. Besides, the surface of PEDOT:PSS film could be easily damaged during dipping treatment. Our research group introduces a new method, dynamic etching process which simplifies two-step dipping process to one-step process and obtains the same effect with dipping process to remove an insulating PSS phase from the surface of PEDOT:PSS film. Basically, the mechanism of the dynamic etching process is the same with dipping process, that is, to remove an insulating PSS phase from PEDOT:PSS film. But the one-step dynamic etching process does not dissolve PSS phase out from PEDOT:PSS film but etches PSS phase off from the surface of PEDOT:PSS film by fast movement of PEDOT:PSS film when etching solvent is added. Even though the effect of the dynamic etching process is

similar to that of dipping process, the dynamic etching process is much easier and simpler. Dipping process spends long time to obtain high conductivity and is conducted in two-step process [19,22]. Meanwhile, the dynamic etching process spends a few seconds for conductivity enhancement and needs only one-step process. Moreover this dynamic etching process is very effective on flexible substrate without any damages thereby the morphology and other properties of PEDOT:PSS are excellent after dynamic etching process. For comparing each process, we prepared four different samples which are pristine PEDOT:PSS, PEDOT:PSS doped with DMSO, PEDOT:PSS with dipping process, and PEDOT:PSS with dynamic etching process to demonstrate the superiority of the dynamic etching process.

2. Experimental The oxygen plasma pre-treatment was performed on a glass substrate for a good wettability with PEDOT:PSS film. We used oxygen gas at 10 sccm of flow rate and oxygen plasma treatment was kept for 10 min at 400 W of rf power. The spin coating technique was used on the glass substrates to form PEDOT:PSS films. The speed of spin coater and time are optimized for PEDOT:PSS film. PH1000, one of PEDOT:PSS series, was obtained from Aldrich and used for the formation of PEDOT:PSS film. Four different samples were prepared as pristine PH1000 (denoted as Sample A), PH1000 doped with DMSO solvent (denoted as Sample B), PH1000 with dipping process using DMSO solvent (denoted as Sample C), and PH1000 with dynamic etching process using DMSO solvent (denoted as Sample D). For the Sample A, pristine PH1000 was spin coated on a glass substrate at 2000 rpm of spin speed for 40 s and then post-annealed at 180 °C for 10 min. For the Sample B, 5 wt.% of DMSO was added in pristine PH1000 solution followed by spin coated and post-annealed as the same condition for Sample A. For the Sample C, spin coated PH1000 was dipped into DMSO solvent for 30 min and post-annealed at 180 °C for 10 min. For the Sample D, 1 ml of DMSO solvent was dropped consecutively onto the surface of Sample A during spinning with 2000 rpm of spin speed for etching PSS from the PH1000 surface. After dynamic etching process, Sample D was postannealed at 180 °C for 10 min as well. The thickness of PH1000 film for each sample was measured by a surface profiler (Tenco-11). For electrical and optical property, four point probe method (MCP-T600) and UV–visible spectrophotometer (Cary 5000) were used, respectively. X-ray photoelectron spectroscopy (XPS, Thermo VG, MultiLab 2000) was performed for investigation of the chemical environment of each sample. Current atomic force microscopy (C-AFM, Seiko E-Sweep) was conducted in order to evaluate the surface current flowing and morphology of the four samples. Four different devices based on four samples used as the anodes were fabricated to compare the device performances. PBDTTT-C:PCBM (poly[(4,8-bis-(2-ethylhexyloxy) -benzo[1,2-b:4,5-b0 ]dithiophene)-2,6-diyl-alt-(4-(2-ethylhexanoyl)-thieno[3,4-b]thiophene)-2,6-diyl] (PBDTTT):

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30 -phenyl-30 H-cycloprop-[1,9](C60-In)[5,6]fullerene-30 -butanoic acid methylester (PC60BM) was coated onto each anode as an active layer. 120 nm-thick Al was deposited on the active layer by thermal evaporation as a top electrode. To evaluate the performance of each device, a Keithley SMU 2400 source meter under AM 1.5 simulated illumination with an intensity of 100 mW/cm2 (PEC-L11) was used. 3. Results and discussion Table.1 shows sheet resistances, thicknesses, and conductivities for pristine PH1000 (Sample A), PH1000 doped with 5 wt.% DMSO (Sample B), PH1000 with dipping process (Sample C), and PH1000 with dynamic etching method (Sample D). In Table.1, the sheet resistances decrease in the order of Sample A, B, C, and D. Sample A has the highest sheet resistance (Rsheet) among the four samples. Pristine PH1000 contains two constituents which are conductive PEDOT and insulating PSS and the conductive PEDOT domains are surrounded by the insulating PSS domains thereby the PSS domains block current flowing. The sheet resistance of Sample B tremendously decreases by adding DMSO [25–27]. It is well-known that materials with high boiling point such as DMSO interact with PSS and PEDOT therefore the path of current opens and charges move along opened PEDOT domains. The conductivity of Sample B increases up to three orders in magnitude compared with the conductivity of Sample A. Meanwhile the sheet resistances of Sample C and D are 159 and 116 X/ sq., respectively. These are lower than that of Sample B (191 X/sq.). Comparing the thicknesses of Sample A–D, the thicknesses of Sample C and D are thinner than those of Sample A and B. This is resulted from the volume difference of PSS removed by dipping or dynamic etching process. The thickness difference between Sample C and D could be explained that PSS existed both inside PEDOT:PSS film and on the surface of PEDOT:PSS film is dissolved out by dipping process for Sample C while only PSS existed on the surface of the PEDOT:PSS film is wiped away by dynamic etching process for Sample D. Therefore the thickness of Sample C is thinner than that of Sample D. Even though the thickness of Sample D is thicker than that of Sample C, the conductivity of Sample D is as high as 1299 S/cm because the sheet resistance of Sample D is lower than that of Sample C. Fig. 1 shows phase and current images of four samples by C-AFM. The color of the surface is changed from the dark brown to light yellow in the phase images of Sample Table 1 The sheet resistance, thickness, and conductivity are described for Sample A through D. Sample A for pristine PEDOT:PSS, Sample B for pristine PEDOT:PSS with 5 wt.% DMSO, Sample C for pristine PEDOT:PSS with dipping process, Sample D for pristine PEDOT:PSS with dynamic etching method. Rsheet (X/sq.) Sample Sample Sample Sample

A B C D

6.3  10 191.0 159.4 116.1

5

Thickness (nm)

Conductivity (S/cm)

71.1 78.1 56.5 66.3

0.2 670.5 1100.4 1299.1

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A to D. In Fig. 1(a), few1 yellow dots are sparsely distributed on the surface and most of other regions are covered with very dark brown phase therefore phase distinction is not observed in Sample A. Sample B shows that elongated ellipsoidal grains start to reveal toward the surface region and dark brown color is covered slightly over those grains. To confirm the path which the charge current flows, the current image is overlapped over the phase image. The inset image of Fig. 1(d) indicates that the charge flows along with yellow region which is grain site. From the observation, the light yellow grains represent PEDOT phase and the dark brown region over grains represents PSS phase, that is, the darker brown region exists, the more PSS phase exists on the surface of PEDOT:PSS film. Accordingly, it is possible to explain the reason that Sample A shows the highest sheet resistance because insulating PSS phase is covered thoroughly over the surface of PEDOT:PSS film. The grains in Sample B rise up to the surface of PEDOT:PSS film as PSS phase shrinks inside PEDOT:PSS film by adding DMSO in PEDOT:PSS thereby the sheet resistance sharply decreases because conductive PEDOT sufficiently exists on the surface. In the phase image of Sample C, there are a lot of yellow grains on the surface of PEDOT while the existence of PSS phase is not verified on the surface. It demonstrates that PSS on the surface of PEDOT:PSS film dissolves into DMSO solvent thus PEDOT phase is exposed on the surface by dipping PEDOT:PSS film into DMSO solvent and the size of PEDOT grain increases because of interaction between PEDOT and DMSO dipping solvent. Meanwhile the phase image of Sample D reveals the lightest yellow region on the surface. It implies that PEDOT phase is dominantly covered all over the surface of PEDOT:PSS, in the other words, PSS on the surface region is effectively removed. The residue of PSS by the dynamic etching process is rarely found on the surface of Sample D thus the sheet resistance of Sample D is lowest among the four samples. It regards that there is no interaction between PEDOT and etching solvent (DMSO) because the grain shape of Sample D is almost the same as that of Sample B. The current image of each sample was monitored for evaluation of the surface current for each sample by C-AFM to find out how PSS phase is affected to a charge current on the surface. The contact mode and tips with Pt/Ir were chosen and 0.3 V of bias was applied to each sample for the current images. Fig. 1(e) through (h) shows the current images of samples. The bright color represents that charge currents are flowing fluently along the surface of PEDOT:PSS film, while the dark color represents that a current flow is impeded because of a high resistance of the surface. As shown in the current images, a current flowing is active in the order of Sample B, C, and D, on the other hand, there is deactivation of the charge current on Sample A. The current flowing is closely related with the conductivity therefore Sample A with the least current flow shows the least conductivity in Table 1. Combined with the results of phase and current images, the more PSS phase exists on the surface, the less charge current flows along the surface. It implies that remained PSS phase blocks the current flow along the surface therefore

1 For interpretation of color in Fig. 1, the reader is referred to the web version of this article.

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Fig. 1. The phase and current images of PEDOT:PSS with different treatment methods by C-AFM. The phase images of (a) through (d) and the current images of (e) through (h). (a) and (e) for pristine PEDOT:PSS (Sample A), (b) and (f) for pristine PEDOT:PSS with 5 wt.% DMSO (Sample B), (c) and (g) for pristine PEDOT:PSS with dipping process (Sample C), (d) and (h) for pristine PEDOT:PSS with dynamic etching process (Sample D), the inset in (d) shows the phase image overlapped with current image of Sample D.

effective removal of PSS phase from the surface is a very important issue to enhance the conductivity of PEDOT:PSS film. The previous results show that the dynamic etching process is the most effective to take PSS phase away from the surface than any other processes. XPS analysis has been conducted for investigation of chemical environment of the samples. The high resolution XPS spectra of Sample A through D in the S 2p region are shown in Fig. 2. The background was subtracted by using the Shirley model, and the charge accumulation effect was corrected with the adventitious carbon as a reference peak at 284.6 eV [33]. XPS spectra of S 2p in binding energy regions for the four samples are shown in Fig. 2(a). The peak between 162 eV and 167 eV is assigned to PEDOT rich region and the peak between 167 eV and 172 eV is assigned to PSS rich region. The peak intensity of PSS rich region is the highest in Sample A and then the peak intensities of PSS region reduce from Sample B to Sample D. While the peak of PEDOT rich region is contrarily developing. For more accurate analysis, peak deconvolution for each sample is accomplished and shown in Fig. 2(b). After peak deconvolution, three S 2p peaks are assigned as pink peak for S 2p in PEDOT (164.13 ± 0.04 eV), green peak for S 2p in PSS-Na+ (165.59 ± 0.08 eV), and blue peak for S 2p in PSS-H+ (168.24 ± 0.10 eV). The relative atomic percentages of different S species are obtained and shown in Table 2. The relative atomic percentage of PEDOT is the lowest in Sample A then PEDOT portion is developed in the order of Sample B, C and D. The relative atomic percentages of PEDOT in Sample C and D are, however, not distinguishable

in deconvolution peak. Table 2 shows relative atomic percentage of each component for Sample A through D. As shown in Table 2, the relative atomic percentage of S in PEDOT is 19.1% and the total atomic percentage of S in PSS is 80.9% for Sample A, the relative atomic percentage of S in PEDOT is 21.3% and the total atomic percentage of S in PSS is 78.7% for Sample B. As adding DSMO solvent into PEDOT:PSS, the relative atomic percentage of S in PEDOT on the surface is relatively reduced than pristine PEDOT:PSS. In the cases of Sample C and D, the ratios of PEDOT remarkably increase, this is, dipping process and dynamic etching process are effective to remove PSS from the surface of PEDOT:PSS film. Comparing Sample C and D, the relative atomic percentage of S in PEDOT is 28.4% for Sample C and that of PEDOT is 29.5% for Sample D. From the result, dynamic etching process is the most effective to remove PSS phase on the surface than any other samples. To compare each surface condition of Sample A–D, optical property and morphology have been investigated. Fig. 3 shows UV–vis spectra in transmittance of Sample A through D. The UV–vis spectra of Sample A and B are almost identical, which means that adding DMSO is not affected to optical property unless the formation of PEDOT:PSS film is failed. Sample D shows almost similar transmittances of Sample A and B over 450 nm of wavelength, however, the transmittance of Sample D becomes higher than that of Sample A and B below 450 nm of wavelength. Otherwise the transmittance of Sample C shows the lowest value in entire UV–vis region and the transmittance is sharply dropped from 350 nm of wavelength. This

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(a)

(b)

S 2p

Sample C

Sample D

Intensity [a.u.]

PSS-H+ PEDOT PSS-Na+ Sample D

Sample A

Sample B

Sample C

Sample B

Sample A

174

172 170 168 166 164 162 172 170 168 166 164 162

172

170

168

166

164

Binding Energy [eV]

162

Binding Energy [eV] Fig. 2. (a) XPS spectra of S 2p binding energy regions between 162 eV and 172 eV for Sample A, Sample B, Sample C, and Sample D. (b) deconvoluted high resolution XP spectra of S 2p binding energy region of each sample, pink color represents PSS-H+, blue color represents PEDOT, and green color represents PSS-Na+.

Table 2 Relative atomic percentages of sulfur in PEDOT, PSS, and DMSO for Sample A–D. Sample Sample Sample Sample Sample

A B C D

S in PEDOT

S in PSS-Na+

S in PSS-H+

19.1 21.3 28.4 29.5

4.2 4.4 7.4 5.8

76.7 74.3 64.2 64.7

Transmittance[%]

100

90

80 Sample A Sample B Sample C Sample D

70

60

300

400

500

600

700

800

Wavelength [nm] Fig. 3. The transmittance of Sample A to D between 200 nm and 800 nm of wavelength. Black hollow square for Sample A, red hollow round for Sample B, blue solid triangle for Sample C, and pink solid line for Sample D. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

phenomenon infers that the surface of Sample C is either damaged during dipping process or blurry because of DMSO dipping solvent residue, which leads to comparably bad transmittance for Sample C. Topography has been examined to confirm precise surface condition of each sample. Fig. 4 represents topography images for Sample A–D. Bright site represents bulged region and dark site rep-

resents valley region. Sample A shows that bright bulged grains are aggregated in a large group. Sample B–D indicate that bright bulged grains are evenly distributed. For formulation of topography, the surface roughness is expressed as root mean square (RMS) value. The surface roughnesses of Sample A, B, C, and D are 6.00, 3.50, 2.55, 2.28 nm, respectively. The morphologies of Sample C and D are smoother than those of Sample A and B. The surface roughness is one of the important factors for organic photovoltaic devices because the morphology condition is influenced to the performance of the devices. The dynamic etching process is effective not only to remove PSS phase but also to form smooth surface from the results of XPS and morphology. (see Fig. 2-4) We have applied four samples as an electrode to organic photovoltaic devices for observing how the characteristics of the electrodes using four samples are affected to the device. Table 3 and Fig. 5 show the performance of organic photovoltaic devices (OPVs) using four samples (A–D) as anodes. The device areas of all samples are 0.36 cm2 with Al top electrode and the control device (reference) is fabricated on commercial ITO glass in the same structure. The performance of OPV device with Sample A is observed on very low efficiency because the sheet resistance of Sample A is extremely high (6.3  105 X/sq.). Therefore the current could not fluently flow through the device with Sample A and the low current density (Jsc) and fill factor (FF) are resulted in 0.60 mA/cm2 and 0.25, respectively. Meanwhile, the sheet resistance of Sample B dramatically decreases to 191.0 X/sq. As the result of the sheet resistance decrease, the performance of the devices with Sample B is considerably progressed. The Jsc leaps up to 10.40 mA/cm2 and FF increases to 0.40 as well. Similarly, due to the reason of reduced sheet resistances of Sample C and D (159.4 and 116.1 X/sq.), Jsc and FF are improved to 9.66 and 10.31 mA/cm2 and 0.44 and 0.46, respectively. The difference of Jsc in Sample B through D is caused by the difference of transmittance in three samples. The Jsc for

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K. Lim et al. / Organic Electronics 15 (2014) 1849–1855

(a)

(b)

(c)

(d)

Fig. 4. The topographies for PEDOT:PSS with different treatment methods by C-AFM. (a) pristine PEDOT:PSS (Sample A) with RMS 6.00 nm, (b) pristine PEDOT:PSS with 5 wt.% DMSO (Sample B) with RMS 3.50 nm, (c) pristine PEDOT:PSS with dipping process (Sample C) with RMS 2.55 nm, (d) pristine PEDOT:PSS with dynamic etching process (Sample D) with RMS 2.28 nm.

Current Density [mA/cm2]

5

Sample A Sample B Sample C Sample D

Table 3 Summary of performances for organic photovoltaic devices using Sample A, B, D, and D as anodes.

0

Reference Sample A Sample B Sample C Sample D

-5

Jsc (mA/cm2)

Voc (V)

FF

PCE (%)

11.10 0.60 10.40 9.66 10.31

0.76 0.74 0.74 0.76 0.75

0.57 0.25 0.40 0.44 0.46

4.76 0.11 3.07 3.23 3.53

-10

-0.5

0.0

0.5

1.0

Bias[V] Fig. 5. Current density–voltage characteristics of organic photovoltaic devices with using Sample A, B, C, and D as an anode under AM 1.5 illumination condition (100 mW/cm2) with 0.36 cm2 of cell area.

Sample B and C are almost equal to 10.40 and 10.31 mA/ cm2 because the transmittances of Sample B and D are

identical between 400 and 600 nm of wavelength. Whereas Jsc of Sample C shows 9.66 mA/cm2 because the transmittance of Sample C is lower than that of Sample B and D. The FF is intimately related with sheet resistance thereby FF is inversely proportional to sheet resistance for each sample. It is also inferred that a delicate difference of FF occurs due to morphology in Sample B through D decreasing in [34,35]. The surface roughness of Sample B, C, and D decrease as 3.50, 2.55, 2.28 nm thus

K. Lim et al. / Organic Electronics 15 (2014) 1849–1855

FF of three samples are somewhat influenced by roughness diminution. 4. Conclusion We prepared four samples by different processes such as pristine PEDOT:PSS (Sample A), PEDOT:PSS doped with 5 wt.% of DMSO (Sample B), PEDOT:PSS with dipping process (Sample C), and PEDOT:PSS with dynamic etching method (Sample D). The sheet resistances of samples decreased in the order of Sample A, B, C, and D. The conductivity of Sample D was 1299 S/cm which is higher than that of Sample C (1100 S/cm) because the sheet resistance of Sample D was lower as 116.1 X/sq. than Sample C (159.4 X/sq.) even though the thicknesses of Sample C and D were different. As shown in C-AFM result, an insulating PSS phase was effectively removed from the surface of PEDOT:PSS film in Sample D thereby the charge current strongly flew along the surface. Besides, the surface condition of Sample D was excellent because the transmittance of Sample D is the highest between 200 and 800 nm, which implies undamaged surface and the morphology of Sample D was the smoothest (RMS 2.28 nm) among four samples. The relative atomic percentage of PEDOT:PSS for Sample D showed the highest value as 29.5% on the surface, which PEDOT phase was exposed the most on the surface of Sample D. According to the results of morphology and charge current, the device performance of Sample D was superior as 10.31 mA/cm2 of Jsc, 0.75 eV of Voc, 0.46 of FF, and 3.53% of PCE. Even though the device performance of the sample doped with DMSO and the sample with dipping process were greatly enhanced, we concluded that dynamic etching method was not only the most contributed to improve the performance of PEDOT:PSS but also very simple and undamaged process in one step for soft electronics. In the future work, we will apply the dynamic etching method for large area electronics and mass production. Reference [1] B. Cotterell, W. Wang, Z. Chen, Eng. Fract. Mech. 69 (2002) 597. [2] Y. Leterrier, L. Me´dico, F. Demarco, J.-A.E. Manson, U. Betz, M.F. Escola‘, M. Kharrazi Olsson, F. Atamny, Thin Solid Films 460 (2004) 156. [3] D.R. Cairns, R.P. Witte II, D.K. Sparacin, S.M. Sachsman, D.C. Paine, G.P. Crawford, Appl. Phys. Lett. 76 (2000) 1425.

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The enhancement of electrical and optical properties of ...

May 10, 2014 - All samples were ... 1566-1199/Ó 2014 Elsevier B.V. All rights reserved. .... dominantly covered all over the surface of PEDOT:PSS, in the.

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