Abstract
The present invention discloses a highly conducting polyethylenedioxythiphene (PEDOT) flexible paper with a very low sheet resistance and high conductivity and process for preparation thereof, by inducing the polymerization at the interface of two immiscible liquids on a cellulose paper to trigger PEDOT growth along the fibers of the cellulose paper. The present invention discloses the use of the said conducting paper for the preparation of flexible supercapacitor and for the preparation of counter electrode in Dye Sensitized Solar Cell (DSSC).
Claims
1. A conducting polyethylenedioxythiphene (PEDOT) coated flexible cellulose paper obtainable by inducing polymerization at the interface of two immiscible liquids on a cellulose paper to trigger PEDOT growth along the fibers of the cellulose paper, wherein the PEDOT coated flexible cellulose paper has a conductivity in the range of 375-400 S/cm.
2. The conducting paper as claimed in claim 1, wherein said paper is useful for the preparation of flexible supercapacitor and counter electrode in Dye Sensitized Solar Cell (DSSC).
3. A process for the preparation of highly conducting polyethylenedioxythiphene (PEDOT) coated flexible cellulose paper comprising the steps of: a) roll coating a paper with FeClO.sub.4 in water to obtain a coated paper; b) interfacial polymerization of the coated paper as obtained in step (a) by roll coating with 3,4-ethylenedioxythiophene (EDOT) in an organic solvent to obtain a single coated conducting paper; c) repeating steps (a) and (b) 5-8 times to obtain multicoated conducting paper.
4. The process as claimed in claim 3, wherein the interfacial polymerization is carried out at temperature in the range of 25-30 C.
5. The process as claimed in claim 3, wherein the interfacial polymerization is carried out for a time period in the range of 1 to 3 hrs.
6. The process as claimed in claim 3, wherein the organic solvent used in step (b) is n-butanol.
7. The process as claimed in claim 3, wherein sheet resistance of the single coated conducting paper as obtained in step (b) is in the range of 20-26 /m.
8. The process as claimed in claim 3, wherein sheet resistance of the multiple coated conducting paper as obtained in step (c) in the range of 2 to 4 /m.
9. The process as claimed in claim 3, wherein the paper that is used is a cellulose paper.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) FIG. 1 depicts a) Schematic representation of the synthetic strategy adopted for the PEDOT-paper preparation, b) larger area PEDOT-paper (40 cm25 cm) made from the present strategy, c) image showing the surface of the clean scotch tape after peeling it from PEDOT-paper surface, d) image of a thin all-solid-state flexible capacitor made from the PEDOT-paper having a thickness of 0.17 mm and e) image of 3.6 V inter-digit supercapacitor made from a single layer PEDOT-paper which glows an LED under flexible conditions.
(2) FIG. 2 depicts a) Variations in the sheet resistance with respect to the number of layers of PEDOT on the paper, b) a plot representing the change in sheet resistance w.r. to time, while keeping the PEDOT paper under ambient conditions (inset shows the contact angle of water on the PEDOT paper), and c) conductivity variations under various flexible conditions.
(3) FIG. 3 depicts SEM images of a) and b) PEDOT-paper formed by interfacial polymerization, c) PEDOT-p-bulk formed when complete reaction happened in pure n-butanol, d) bare cellulose paper. e) and f) TEM images of PEDOT formed through interfacial polymerization.
(4) FIG. 4 depicts a) XRD spectra and b) UV-visible spectra of various samples. S2p XPS spectra of c) PEDOT-p and d) PEDOT-bulk.
(5) FIG. 5 depicts a) Cyclic voltamograms recorded at 50 mV/s, b) charge-discharge (CD) profiles of PEDOT-p taken at a current density of 0.4 mA/cm.sup.2 with different layers of the PEDOT coating, c) enlarged view of the CD profiles given in b indicating the differences in the IR drop, d) areal capacitance measured for the various PEDOT-p, e) CD profiles of PEDOT-p-5 taken at various current densities and f) graphical representation of the capacitance changes of PEDOT-p-5 with respect to the varying current density values.
(6) FIG. 6 depicts a) Nyquist plot of the flexible device made from PEDOT-p-5 with the enlarged high frequency region along with the circuit diagram is given in the inset, b) CD profile of the PEDOT-p at a various bending and flexible conditions and c)-d) represent the long-term cycle stability data.
(7) FIG. 7 depicts a) CD profiles of the inter-digital supercapacitor in a voltage window of 3.6 V at various bending and flexible conditions and b) Ragone plot; inset image shows the thickness of the sandwiched device.
(8) FIG. 8 depicts a) CV profiles recorded at a scan rate of 10 mV/s and b) Tafel polarization plots in the asymmetrical dummy cell.
(9) FIG. 9 depicts I-V polarization curve of a solar cell using the PEDOT paper as the counter electrode in comparison with Pt/FTO.
(10) FIG. 10 depicts a) PEDOT polymerization on cellulose paper through various solvent combinations. B) Optical images of the corresponding PEDOT paper.
(11) FIG. 11 depicts CV profile at 10 mV/s of PEDOT-bulk and coated on a solid current collector.
DETAILED DESCRIPTION OF THE INVENTION
(12) The present invention provides an efficient and scalable method to prepare highly conducting PEDOT flexible paper which possesses a very low sheet resistance, wherein said method comprises inducing the polymerization at the interface of two immiscible liquids on a cellulose paper to trigger PEDOT growth along the fibers of the cellulose paper.
(13) This type of substrate assisted alignment is found to have a key impact on the conductivity as well as the electrochemical activity of the PEDOT films. The prepared PEDOT film possess highly ordered polymer chains and increased doping level, which help the paper to display excellent conductivity even at flexible conditions. The prepared film adheres strongly to the substrate and retains the flexible nature of the cellulose paper and maintains long-term stability on the conductivity.
(14) The present invention provides a process for preparation of highly conducting polyethylenedioxythiphene (PEDOT) flexible paper, wherein said process comprising the steps of: a) Roll coating the paper with FeClO.sub.4 in water; b) Roll coating the paper of step (a) with EDOT in suitable organic solvent; c) Allowing a process of interfacial polymerization to occur to afford highly conducting paper,
(15) Characterized in that, conductivity of the said paper is up to 400 Siemens/cm.
(16) The steps (a) and (b) are repeated to afford multilayer conducting paper. The interfacial polymerization is carried out at temperature in the range of 25-30 deg C. The said interfacial polymerization is carried out for a period in the range of 1 to 3 hrs.
(17) The organic solvent in step (b) selected from n-butanol. The conductivity of said conducting paper is 375 Siemens/cm. The sheet resistance of said conducting paper is in the range of 3 to 26 /cm. The said conducting paper is cellulose paper
(18) The conducting paper is used for the preparation of flexible supercapacitor. The conducting paper is also used for the preparation of counter electrode in Dye Sensitized Solar Cell (DSSC).
(19) Due to the hydrophilic nature of FeClO.sub.4, there will be always a thin layer of water associated with it and this creates an interface which is immiscible with EDOT/n-butanol. Thus, formation of this interface controls the growth kinetics of PEDOT and ensures an aligned and thin coating the fibers of the paper by the polymer. Schematic representation of the synthetic procedure adopted in the present invention is shown in FIG. 1a. One of the key highlights of the synthetic strategy adopted here in the invention is its scalability compared to other methods. PEDOT film impregnated flexible paper (hereinafter called PEDOT-p) may be prepared in a scalable way by bar coating. Photograph of a prepared PEDOT-p having an area of 40 cm25 cm is shown in FIG. 1b. The PEDOT layer attains strong adhesion with the substrate as revealed from the scotch tape experiment (FIG. 1c).
(20) The sheet resistance and conductivity is measured using the four-probe method. The sheet resistance obtained for PEDOT-p-1 is 24 /m (FIG. 2a), which could be further reduced up to 3 /m (PEDOT-p-5) by multiple coatings. For comparison, the inventors have prepared PEDOT by dissolving both EDOT and FeClO.sub.4 in pure n-butanol on the cellulose paper (PEDOT-p-bulk) using the same protocol. Due to the poor control on the polymerization process in this case, the sheet resistance has been shoot up to 10 M/m, compared to 24 /m for PEDOT-1. The measured conductivity of PEDOT-p-5 is 37525 S/cm, considering the thickness of the PEDOT film as 81 m. For comparative studies, inventors prepared PEDOT powder from pure n-butanol by normal solution method, which hereafter is termed as PEDOT-bulk. Compared PEDOT-p (37525 S/cm), the conductivity of PEDOT-bulk is only 30 S/cm. The observed low sheet resistance of PEDOT-p-5 is stable even up to 90 days under ambient conditions (FIG. 2b). This conductivity retention is far better than a previous report and the PEDOT prepared using a wet chemistry method. High hydrophobic nature of the PEDOT paper, which repels the water moisture from entering its matrix, helps for displaying the stability at the ambient conditions. Contact angle measurement shows its hydrophobic nature with a water contact angle of 131, which is much higher than that displayed by PEDOT-bulk (55) and samples listed in the previous few reports (inset of FIG. 2b). Further, inventors carried out the I-V (current-voltage) measurement of the PEDOT paper at various bending and twisting conditions and it is found to be very stable, even with twisted and bending conditions where superimposed IV-plots are obtained (FIG. 2c). The minimum sheet resistance obtained in the present case is 3 /m, which is much lower than the sheet resistance displayed by the present ITO and FTO coated glass (7-14 /m) and Au sputtered substrates (5 /m for a 30-35 nm thick Au).
(21) The scanning electron microscope (SEM) images of FIG. 3a shows the surface morphology of the bare cellulose paper, where the surface of the paper is found to have micron sized cellulose fibers. After the PEDOT coating, the surface morphology does not have any visible changes at low resolution (FIG. 3b). This is due to the uniform coating of PEDOT along the cellulose fibres rather than at the vacant spaces. This may be explained from the hydrophilic interaction between the OH groups in the cellulose with FeClO.sub.4. This eventually helps the PEDOT for polymerization only on the fiber surface. Due to the same reason, the formed PEDOT displays strong adhesion to the substrate in such a way that the polymer layer could withstand while trying to peel it out with the help of a scotch tape (FIG. 1c). This type of strong interaction is not observed in most of the PEDOT films formed by the conventional ways due to the lack any interaction between the substrates and the PEDOT films. At higher magnification (FIG. 3c), the image clearly indicates that the PEDOT layer possesses mostly a fiber type growth pattern having an average thickness of 200-300 nm and length of several micrometers. FIG. 3d shows the SEM surface images corresponding to the PEDOT-p-bulk. It is clearly visible in this case that the PEDOT is not formed uniformly, rather it has short and orderless bulk PEDOT structure with relatively low yield.
(22) The Transmission electron microscopy (TEM) images of the instant PEDOT as shown in FIGS. 3e & 3f reveals that PEDOT formed during interfacial polymerization according to the invention possesses 3-D porous structures.
(23) The XRD spectra (FIG. 4a) shows two strong peaks at 15.7 (110) and 22.5 (002) for the cellulose paper, which are the characteristic peaks of cellulose Apart from the above peaks, characteristic peaks of PEDOT at 6.7 and 26.3, corresponding to the (100) and (002) planes, respectively, are visible in the PEDOT paper and PEDOT-bulk. The (100) spacing is in relation with the inter--conjugated chain distance of the stacked PEDOT polymer. Interestingly, the relative intensity of the (100) to (020) planes is high (3.5) in the PEDOT paper compared to that in the bulk PEDOT (1.1). This serves as an indirect evidence for the existence of more ordered PEDOT chains, which helps for the better inter-chain interaction and, thereby, efficient charge-hopping between the chains compared to PEDOT-bulk.
(24) More conclusive evidence about the level of doping has been obtained from the sulphur XPS spectra of PEDOT-bulk and PEDOT-paper presented in FIGS. 4c and d, respectively. The deconvoluted peaks appeared at 162.3 and 163.6 eV correspond to the S2p3/2 and S2p1/2 states, which shows a ratio of 2:1 for the area under the peak and a B.E difference of 1.3 eV. The third peak (166.3 eV) correspond to the partially oxidised sulphur (S.sup.+),which is balanced by the doped counter ion either ClO.sup.4 or Cl.sup.. Remarkable difference is found in the relative intensity of S.sup.+ with neutral S in PEDOT-paper, indicating the pronounced doped counter ion. Quantification of doping level is done by taking the ratio of area under the peak of Cl 2p to S 2p, which is found to be 0.32 in case of PEDOT-p and 0.23 for PEDOT-bulk (Table 1 and 2).
(25) TABLE-US-00001 TABLE NO. 1 Peak parameters of PEDOT-p Peak Position (eV) Area FWHM (eV) 0 (S2p 3/2) 162.325 2983.912 1.791 1 (S2p 1/2) 163.636 1421.953 3.620 2 (S.sup.+) 166.271 2026.226 4.29 Cl 2p 206.558 2702.512 2.842
(26) TABLE-US-00002 TABLE NO. 2 Peak parameters of PEDOT-bulk Peak Position (eV) Area FWHM (eV) 0 (S2p 3/2) 162.316 12945.400 1.954 1 (S2p 1/2) 163.737 6291.283 2.039 2 (S.sup.+) 166.200 5619.563 4.575 Cl 2p 206.234 7880.315 3.271
(27) Further, enhanced doping implies more -conjugation which will lead to red shift in the absorption in the UV-visible spectra. As expected, in the interfacial polymerized PEDOT, a clear red shift has been observed due to higher doping compared to PEDOT-bulk (FIG. 4b). Insufficient doping in PEDOT-bulk could also be confirmed from the less intense peak at around 560 nm, which is a trademark of the -* transition of neutral PEDOT, and will vanish after complete oxidation as occurred in the interfacial polymerized PEDOT sample. Thus the above two critical factors helps for PEDOT-p to achieve a high conductivity of 375 S/cm compared to 31 S/cm obtained for PEDOT-bulk as measured by the DC four-probe method.
(28) FIGS. 5a and 5b show the CV and CD profiles obtained from solid-state devices made from PEDOT-p-1 to PEDOT-p-5. Capacitance properties are found to be improving linearly with increasing the PEDOT layer in the paper due to the increasing amounts of PEDOT as well as due to the progressively reduced sheet resistance. Areal capacitance is found to be increased from 28 mF/cm.sup.2 to 115 mF/cm.sup.2 while the coating is increased from 1 layer to 5 layers (FIG. 5d). The PEDOT amount on the 5 layered PEDOT paper (i.e. PEDOT-p-5) is around 1 mg/cm.sup.2 and the corresponding mass specific capacitance is estimated to be 115 F/g, which is substantially higher than that measured on the system derived from PEDOT-bulk (60 F/g) (tested by coating on a carbon paper, FIG. 11). Considering the highest capacitance registered by the system derived from PEDOT-paper. The detailed investigations are restricted by focusing on this system. The capacitance measured by the device made from PEDOT-p-5 is much higher or even comparable to values reported in the literature on the PEDOT based capacitors using solid current collectors (Table 3). Rather than mass specific capacitance, it is desirable to state the capacitance in volumetric and areal density, as they are the two important parameters for judging the feasibility of the material for practical usage. A volumetric capacitance of 144 F/cm.sup.3 is obtained at a current drag of 0.5 A/cm.sup.3 by considering the thickness of PEDOT as 8 m in PEDOT-paper-5 (FIG. 5f). This value of capacitance is much higher compared to the values available for the recent literatures (a comparative literature data is tabulated in Table 3). Even at a high current drag of 10 A/cm.sup.3, the present system retains up to 90 F/cm.sup.3 (details are given in FIGS. 5e and 5f), indicating the superior power rate of the device. Apart from the high conductivity of PEDOT (>375 S/cm), the porous structure as found in TEM also helps for maintaining the high capacitance by achieving high electrode-electrolyte interface during the intercalation of the polymer gel electrolyte.
(29) TABLE-US-00003 TABLE 3 Comparative literature survey Window Current Electrode Energy density Power Density (V) collector PEDOT-cellulose 1 mW/cm.sup.3 0.05 W/cm.sup.3 1.2 No current paper Current Work* 28 mW/cm.sup.3 1.52 W/cm.sup.3 collector Transparent carbon 47 Wh/cm.sup.3 19 mW/cm.sup.3 1 No current film collector HTiO.sub.2 @MnO.sub.2 0.30 mWh/cm.sup.3 0.23 W/cm.sup.3 1.5 Carbon cloth HTiO.sub.2 @C Core-Shell 59 Wh/kg 45 kW/kg.sup.1 PANI/Au/Paper 10 mWh/cm.sup.3 3 W/cm.sup.3 0.8 Au coated Paper NPG-PPy 19 mWh/cm.sup.3 283 W/cm.sup.3 0.75 Porous Gold 2.8 mWh/cm.sup.3 56.7 W/cm.sup.3 electrode Hetero doped 16.9 mWh/cm.sup.3 4560 W/cm.sup.3 1 Au Current Graphene collector
(30) The inventors have further pushed the devices for stringent stability test at various bending and flexible conditions. Initially, CD profile is measured at various bending and twisted conditions (FIG. 6b) and the data is found to be closely superimposable. Due to the highly flexible nature of the individual components like cellulose, PEDOT and PVA-H.sub.2SO.sub.4 gel, the device appears quite robust to the various flexible conditions. Further, long-term stability test is carried out under normal condition for 2500 cycles by applying continuously a current density of 2 mA/cm.sup.2. The performance of the system is found to be very stable (9% degradation) while maintaining high coulombic efficiency (99%) throughout the cycles. Long-term cycle stability of the devices at various bending and twisted conditions also is monitored and found to be very stable even after 3800 cycles. Small degradation found in capacitance is due to the loss of water from the gel due to the heat generation during the cycles, which wehighlighted in our previous reports as well. The energy density and power density of the device are calculated and the values are tabulated in the form of a Ragone plot in FIG. 7b. A maximum energy density of 28 mWh/cm.sup.3 is obtained for the PEDOT. The above value obtained for the PEDOT is quite higher compared to many of the flexible thin supercapacitors listed in the recent literature (Table 3). The inventors also have calculated the energy density and power density by considering the whole device thickness (0.17 mm, FIG. 8b) and the value is found to be 1 mWh/cm.sup.3 at a power density of 52 mW/cm.sup.3 and the system could retain an energy density of 0.61 mWh/cm.sup.3 even at a higher power drag condition of 1 W/cm.sup.3.
(31) As mentioned in the previous embodiments, large scale production of PEDOT paper is simple and may be improvised into various designs and shapes. It should be noted that the total device thickness is only 0.17 mm which includes electrode, electrolyte and separator in the integrated form. However, that this thickness may be further reduced by reducing the thicknesses of the polymer electrolyte (0.1 mm) and cellulose paper (0.6 mm), which come around 90% of the total thickness in the present device. An inter-digital flexible solid-state-supercapacitor is made from a PEDOT paper with a working potential of 3.6 V (FIGS. 1e and 7a). The device consists of 3 capacitors connected in series in a single PEDOT paper where, the PEDOT phase itself acts as the electric connector between them. The CD profile of the device is shown in FIG. 7a and the image of the glowing LED using the device in the flexible condition is shown in the inset of FIG. 7a. Similar to sandwiched supercapacitor, inter-digital supercapacitor has also been found to be very stable to the flexible conditions, where the CD profiles are superimposable in the bending and twisting conditions. Therefore, the method of preparation of highly conducting PEDOT-p of the instant invention may be further extended to screen printing and may be used to prepare designer flexible supercapacitors.
(32) FIG. 8a shows the CV profiles of PEDOT-p-3 to PEDOT-p-5 recorded at a scan rate of 10 mV/s. As indicated in the FIG. 8a, first redox peaks corresponds to the I.sup./I.sub.3.sup. redox couple and second one corresponds to I.sub.3.sup./I.sub.2 couple. Among the various samples, PEDOT-p-4 possesses the highest reduction current as well as the lowest difference between the potential at reduction and oxidation peak current maxima for I.sup./I.sub.3.sup. couple, which are characteristics of the high catalytic activity towards the tri-iodide reduction. Further, square root of the scan rate has a linear relationship with the peak current density in the case of PEDOT-p-4, indicating the involvement of a diffusion limited reaction and absence of any interaction of ions with the substrate. Thus, inventors have selected PEDOT-p-4 as the right candidate for deploying as the counter electrode in real DSSC measurements. Before going to a real cell, inventors further confirmed the activity of PEDOT-p-4 by using Tafel polarisation using symmetric cell at a scan rate of 10 mV/s. It may be seen that PEDOT-p-4 displays similar limiting current as that of the standard Platinum coated FTO (Pt/FTO). However the exchange current density which measured at lower over potential is high for Pt/FTO (2.2 mA/cm.sup.2) than PEDOT-p-4 1.2 mA/cm.sup.2). This deviation arises due to the movement of I.sub.3.sup. and I.sup. inside the PEDOT matrix during the redox reaction, which is hampering the electrical conductivity of PEDOT. A real DSSC cells are fabricated using PEDOT-p-4 as the counter electrode and FTO/TiO.sub.2/Dye as working electrode (details of the cell fabrication is given in experimental section). Cell's I-V polarisation plots are given FIG. 9a. An overall solar conversion efficiency of 6.5% has been obtained for the system derived from PEDOT-p-4 compared to 7% efficiency displayed by the system having Pt/FTO as the counter electrode. Coming to the individual parameters, PEDOT-p-4 based system shows superior fill factor of 66% compared to 62% of the system made from Pt/FTO, indicating the high catalytic activity. However, lower short circuit density (J.sub.sc) of 13 mA/cm.sup.2 in comparison to 15 mA/cm.sup.2 of Pt is deleteriously effect the overall efficiency of the present flexible counter electrode. Lower open circuit potential (OCV) and low J.sub.sc arises as there is no external current collector, rather catalyst should play the dual role of I.sub.3 reduction and charge mobility. However the presented flexible material is still promising due to its comparable catalytic activity with costly Pt coated FTO. Thus, PEDOT-paper-4 shows great potential to replace Pt and TCO from the counter electrode. Different PEDOT paper used cell test data are given in Table 4, in which PEDOT-4 is showing superior activity in accordance with the CV data.
(33) TABLE-US-00004 TABLE 4 IV measurement parameters Sample Voc Fill Factor Jsc mA/cm.sup.2 % Efficiency PEDOT-p-3 0.67 68.36 9.83 4.53 PEDOT-p-4 0.74 66.45 13.06 6.46 PEDOT-p-5 0.66 70.50 11.86 5.55
EXAMPLES
(34) Following examples are given by way of illustration therefore should not be construed to limit the scope of the invention.
Example 1
Preparation PEDOT Paper
(35) In a typical preparation method, a butter paper having an area of 911 cm.sup.2 was placed over a bar coater and 340 mg of FeClO.sub.4 in 0.5 ml water was coated over it using a rod with a groove spacing of 40 m at a speed of 3 meter/minute. The paper was kept for drying at 25 deg C. Further 25 l of EDOT in 0.5 ml n-butanol was bar coated over FeClO4 coated paper with the same speed. The paper was left for drying and polymerization. After 2 h, the paper was washed several times in ethanol until the excess FeClO4 was removed. The paper was dried and smoothened by keeping in a press (Carver) at a pressure of 12 MT for 2 min. For achieving a low sheet resistance, the process is repeated several times. From the second layer onwards, the FeClO4 was coated initially in n-butanol instead of water as the PEDOT layer is hydrophobic. After drying out the n-butanol, the paper was kept under a humidity chamber by maintaining a relative humidity of 70% for 15 min. for allowing FeClO4 to absorb water. Except this step, all the remaining processes are kept same as that of the first coating step.
Example 2
Preparation of PVA-H2SO4 Solutions and Film
(36) 1 g of PVA was dissolved with vigorous stirring at 85 C. for 2 h in 50 ml RB containing 10 ml of de-ionized water. The above solution was left for cooling to room temperature and at this stage, drop-wise addition of 1.0 g H.sub.2SO.sub.4 was carried out under stirring condition. Viscosity of the obtained solution was 0.6105 Pa.Math.s.
Example 3
Prototype Flexible Supercapacitor Fabrication
(37) The above prepared PEDOT paper was laminated using a PVA film (2 m) by hot pressing at 120 C. for 2 min on the non-conducting side. The laminated PEDOT paper was then cut into pieces having specific areas (here 2.5 cm2) and is coated with a PVA-H2SO4 solution using a bar coater. Small region was left vacant for giving electrical contacts. The space kept for the electrical contact in the butter paper was coated with Ag paste. For making inter-digital supercapacitor, PEDOT paper was cut into specific dimensions and sealed in a PVA films. 3-cell was made in a single paper in series with total size of 14 cm3.8 cm which includes the free space between the electrodes.
Example 4
Characterization of Electrode and Cellulose Substrate
(38) Structure and morphology of the materials was analysed by Quanta Scanning Electron Microscope and Nova Nano SEM 450. High-resolution transmission electron microscope (HR-TEM) was carried out in Tecnai-T 30 at an accelerated voltage of 300 kV. Philips X'pert pro powder X-ray diffractometer (Cu K radiation, Ni filter) was used for X-ray Diffraction (XRD). X-ray Photo electron Spectroscopic (XPS) measurements were carried out on a VG Micro Tech ESCA 300 instrument at a pressure of >110-9 Torr (pass energy of 50 eV, electron take off angle of 60 and the overall resolution of 0.1 eV) Horiba JobinYvon Inverted Lab RAM HR800 VIS-NIR using 532 nm solid state diode laser beams was used for Raman analysis. All the electrochemical studies were carried out in a BioLogic VMP3 multichannel Potentio-Galvanostat. The CV measurements were taken at different scan rates from 10 to 100 mV/s by maintaining a potential window of 1.2 V for single devices. The charge-discharge measurement was done at different current densities (0.5 to 10 mA) in the potential range of 0-1.2 V. Cycling stability was done by chrono charge-discharge method at a current density of 5 mA for 2500 continuous cycles and followed by 3800 cycles including bending and twisted modes. Electrochemical impedance (EIS) analysis was carried in an a.c frequency range of 106-0.01 Hz in the open circuit potential with a sinus amplitude of 10 mV (Vrms=7.07 mV). All the EIS data were analysed and fitted using an EC-Lab Software V10.19. Inter-digital flexible capacitor is tested by charge discharge method at current density of 0.5 mA in a voltage window of 3.6 V in bended, flexible and folded modes. Four-probe conductivity meter having a probe spacing of 0.2 mm were used for electrical conductivity measurements. Conductivity changes in flexible conditions were measured by 2 probe method using linear sweep voltametry (LSV).
Example 5
Counter Electrode Characterization
(39) The CV measurements were carried out in distilled acetonitrile containing 0.1 M LiClO4, 5 mMLiI and 0.5 mM 12 under N2 atmosphere. A 3-electrode setup was used for the CV measurement in which the prepared counter electrode for DSSC was used as the working electrode and Pt wire which was internally calibrated using ferrocene/ferrocenium (Fc/Fc+) couple was used as the reference electrode. 0.64 cm2 area of PEDOT-p working electrode was exposed to electrolyte by masking and remaining portion with adhesive tape. Pt foil was used as the counter electrode. Tafel measurements were done in symmetrical cell in which potential was polarised from 1 to +1 V at a scan rate of 10 mV/s.
Example 6
Dye Sensitized Solar Cell (DSSC) Fabrication
(40) A previous reported method was used for making Standard P25 paste. FTO working electrode, were washed by ultra-sonication in soap solution, deionized water and absolute ethanol. The P25 paste was doctor bladed on the washed FTO until 12-13 microns was achieved by multiple coatings followed by annealing for 1 h. Following a previous method, TiCl4 treatment was done over the working electrodes and flowed by heating at 450 C. for 30 min. The working electrodes were socked in 0.5 mM N719 dye solution for overnight. DSSCs were assembled using a sandwich assembly of the working electrode and flexible PEDOT counter electrode. The electrolyte used was a mixture of 1 M DMPII, 0.05 M LiI, 0.05 M I2 and 0.5 M tert-butyl pyridine. I-V (current vs. voltage) measurements were done under Newport Solar Simulator attached to Keithley 2420 source meter.
ADVANTAGES OF THE INVENTION
(41) 1. Easy to scale up
(42) 2. Variety of application possible
