Sheet resistance and transmittance of PDZ-coated graphene samples as a function of the number of PDZ layers. Optical properties of the surface and interface of GL-TE structure. a) Ultraviolet photoelectron spectroscopy of three different types of films. Evaluation of thermal stability and estimated lifetime of the graphene-coated organic films. a) Changes in the skin resistance of as a function of temperature.
Introduction to Transparent Electrodes
- Transparent electrodes
- Graphene
- Conducting polymer
- Other transparent electrodes
To overcome low electrical conductivity, diverse functionalization methods of PEDOT:PSS have been developed. Furthermore, since the wetting properties of PEDOT:PSS solution can be improved by fluorosurfactant, PEDOT:PSS solution treated with facile functionalization can have excellent compatibility with other transparent electrodes. Moreover, its acidic nature of PSS can corrode adjacent layers, including inorganic electrodes, such as ITO, and active layer in optoelectronics.29–31 In the case of ITO/PEDOT:PSS structure, de Voigt et al.
Synthesis of Graphene and functionalization of PEDOT:PSS for high-performance
- Introduction
- Experimental section
- Results and discussion
- Facile functionalization in PEDOT:PSS solution
- Structural and optoelectrical characteristics of PDZ-coated CVD graphene
- Summary and Outlook
Wetting properties of bare PEDOT:PSS and functionalized PEDOT:PSS (PDZ) were measured by analyzing contact angles (Phoenix 300). Contact angles of pristine PEDOT:PSS (contact angle ~ 69°) and functionalized PDZ (contact angle ~ 17°) on CVD-Gr. Raman spectra of PDZ-coated graphene SiO2/Si (black line), PDZ film on SiO2/Si (red line) and as-grown CVD graphene on SiO2/Si (blue line).
Fabrication of graphene/PEDOT:PSS composite on various plastic substrates
Introduction
In this chapter, based on the previous study on facile functionality of PEODT:PSS and PDZ/Gr hybrid TE structures, we developed a new fabrication method for graphene-based hybrid TE structures using a lamination process. The lamination process allows as-grown CVD graphene to be directly transferred to the desired substrate, such as glass, polyethylene terephthalate (PET), urethane, PDMS and so on, uniformly and conformably. Without unnecessary PMMA support layer or other disturbances, a clean interface can be formed in Gr/PDZ films and the contact resistance between graphene and PDZ layers is reduced.
In addition, the optoelectric properties of Gr/PDZ films can be optimized by controlling the PDZ thickness. In addition, for operational stability tests, Gr/PDZ samples were evaluated under adverse environments such as mechanical and thermal loads, high temperature and high humidity.
Experimental section
The calculation of μ = σ|RH|, gave us the estimated Hall mobility, in terms of thickness and sheet resistance of the samples. The transfer length (LT) and RS of the favorable layer can be measured by the well-known CTLM equation, RT = (RS/2π){ln(1 + S/rI) + LT(1/rI + 1/(rI) + S))},42,43 where rI is the inner contact radius, RT is the total resistance between the outer and inner contacts, and S is the contact pad spacing. Ultraviolet Photoelectron Spectroscopy (UPS): UPS analysis was applied to investigate the work functions of the samples.
During both stability tests, the resistance of the samples was measured as a function of time at a constant applied voltage of 1 V (Keithley 2636A). Thermal Stability: We implemented operational stability under thermal stress by evaluating the change in the plate resistances of the samples as a function of temperatures between 25 and 210 °C using the four-probe station with a hot plate function applied by an Agilent source meter B1500A. A plot of the logarithm of the rate of rise versus the reciprocal temperature at a constant level of decomposition provided the activation energy.
In Figure 3.5, the estimated time to failure tf can be calculated from Toop's relation by entering previously obtained parameters of activation energy E, constant b and constant failure temperature Tf. By calculating the estimated time for several failure temperatures, a plot of the estimated lifetime as a function of the corresponding reciprocal temperature for 20 mass% loss was obtained. TGA weight loss curves of GL-TE films at different ramping rates of 1, 2, 5, and 10 °C/min and the transformed logarithm of the heating rate vs.
Calculation of the activation energy (E) from the slope of the lines in the figure x, using the method of Flynn and Wall (repetition method).
Results and discussion
- Structural characteristics of graphene-laminated transparent electrodes
- Electrical and optical characteristics of graphene-laminated transparent electrodes
- The role of graphene in the charge transport of the hybrid structure
- Environmental stability tests of graphene-laminated transparent electrodes
This improvement can affect the morphologies of the GL-TE film, by reducing the number of wrinkles, tears and air voids. Since the estimated charge carrier density was decreased by more than two orders of magnitude, the mobility of GL-TE could be simultaneously improved. We can check that the sheet resistance of the GL-TE samples initially decreased significantly as a result of the bulk resistance.
As a result, the Fermi level of graphene in GL-TE samples will drop significantly from the Dirac point. 18 cm−1 from the position of the G peak in CVD graphene at 1586 cm−1, demonstrating the interfacial p-type doping of graphene in the GL-TE film. As shown in Figure 3b, we can confirm the temperature dependence of the reduced activation energy for the PDZ/PET and GL-TE films.
The effect of mechanical bending on our GL-TE films was evaluated using 5000 consecutive bending cycles as shown in figure 3.11a, which shows the change in the resistance of the GL-TE films as a function of the number bending cycles. In figure 3.11, our results showed that graphene barrier can protect the GL-TE samples from the exposure of the samples to UV light (λ = 254 nm). As the PET substrate with a low glass transition temperature is thermally degraded above 150 °C,54 there was a sudden increase in the sheet resistance of the GL-TE film.
In other words, the introduction of a graphene layer in the organic TE films contributes to the higher overall stability in the GL-TE film due to the outstanding thermal dissipation of the graphene layer.6,59.
Summary and Outlook
Fabrication of Graphene/Acid-Treated PEDOT:PSS Anode through Colorless
Introduction
In addition, due to the synergistic effect of the three-layer geometry, the TCPI/Gr/MSA-PDZ-based PLED at the anode showed excellent current and power efficiency higher than that of the ITO-based PLED. In addition, the TCPI/Gr/MSA-PDZ anode-based PLED can withstand more than 500 cycles of bending tests at a bending radius of 5 mm. The three-layer graphene-based composite has shown great potential for practical use in large-area flexible optoelectronics and is a promising candidate for next-generation flexible optoelectronic devices due to its excellent optoelectric performance and operational stability.
Experimental section
Methanesulfonic acid (MSA) with a pKa ~ -1.9 was used to further functionalize the PDZ films, followed by heating at 160 °C for 3 min. The structural features of the TCPI/Gr/MSA-PDZ, TCPI/Gr and CVD graphene samples were analyzed by tapping AFM. The conventional four-point probe method was evaluated for measuring sheet resistances (Rs) of thin films using a Hall effect system (Lakeshore Model 642).
In order to evaluate the gas barrier effect of graphene, water vapor transmission rate (WVTR) analysis was performed using a PERMATRAN-W 3/33 MG PLUS (MOCON) equipment at 38 °C and 100 RH% with a detection limit of 0.005 g m. -2 per day. UPS measurements were performed to investigate the work functions of the samples on an Axis-NOVA (Kratos. Inc.) (base pressure 10−7 Pa) with a pass energy of 1.0 eV at 0.05 eV per step, using the non-monochromatic He I to use. radiation (21.2 eV). An atomically clean Au helps to measure the energy calibration and ensures accurate values for Fermi edge before measurement, while -15 V bias is applied for improvement in the secondary photoelectron cutoff.
UPS measurements were implemented to measure the work function of samples, which can be measured from ϕυ = hυ − |Ecutoff − EFE|, where hυ. As an electron injection layer and cathode material, a LiF (1 nm)/Al (100 nm) cathode was deposited by thermal evaporation processes in high vacuum (~10−7 torr), with deposition rates of 0.1 and 1.0 Å s−1. , respectively. The J−V−L characteristics of the flexible PLEDs were analyzed using a Keithley 2400 source measurement unit and a Konica Minolta CS-2000 spectroradiometer, before and after cyclic bending.
At least 10 devices were measured for average PLED performance for accuracy.
Results and discussion
- Structural characteristics of TCPI
- Structural characteristics of TCPI/Gr/acid-treated PDZ
- Optoelectrical characteristics of TCPI/Gr/acid-treated PDZ
- Environmental stability of TCPI/Gr/acid-treated PDZ
- Application of TCPI/Gr/acid-treated PDZ in PLED
In Figure 4.8a, for the TCPI/Gr/MSA-PDZ film, the resistance only increases by ~8 Ω/sq, after 10,000 cycles of bending stress, showing no significant visible cracks or tears. In other words, due to excellent structural properties, the TCPI/Gr/ MSA-PDZ films showed excellent endurance under mechanical bending stress. After the temperature approached 260 °C, the resistance of the TCPI/Gr/MSA-PDZ film began to increase gradually.
As a result, the TCPI/Gr/MSA-PDZ sample can endure 47.3 and two times slower than the barrier-free bare PDZ film and graphene-free TCPI/MSA-PDZ, respectively. -manufactured) TCPI/Gr/MSA-PDZ(2L) After 7 days thermal stability test After 15 hours humidity stability test After 5 cycles of long term stability test. a-b). Through the previous studies, we can demonstrate that TCPI/Gr/MSA-PDZ films have a potential viability for practical flexible optoelectronics.
Through UPS analysis, we can check that the TCPI/Gr/MSA-PDZ anode has adequate work function of 5.04 eV for efficient hole injection (Figure 4.15 and Table 4.1). Due to the low surface roughness and clean interface, there is no large leakage current in TCPI/Gr/MSA-PDZ-based PLEDs, which is the same as glass/ITO-based PLED devices (Figure 4.16b). Furthermore, we can successfully fabricate flexible PLED devices based on TCPI/Gr/MSA-PDZ anodes, as shown in Figure 4.16e, showing uniform illumination without noticeable degradation at a bending radius of ∼2.3 mm.
In other words, the TCPI/Gr/MSA-PDZ film showed great potential for commercial viability in flexible optoelectronics, due to excellent optoelectric properties, great operational stability, and the simple large-area fabrication method.
Summary and Outlook
Conclusion
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