Improvement of organic solar cells by flexible substrate and ITO surface treatments

In this paper, surface treatments on polyethylene terephthalate with polymeric hard coating (PET-HC) substrates are described. The effect of the contact angle on the treatment is first investigated. It has been observed that detergent is quite effective in removing organic contamination on the flexible PET-HC substrates. Next, using a DC-reactive magnetron sputter, indium tin oxide (ITO) thin films of 90 nm are grown on a substrate treated by detergent. Then, various ITO surface treatments are made for improving the performance of the finally developed organic solar cells with structure Al/P3HT:PCBM/PEDOT:PSS/ITO/PET. It is found that the parameters of the ITO including resistivity, carrier concentration, transmittance, surface morphology, and work function depended on the surface treatments and significantly influence the solar cell performance. With the optimal conditions for detergent treatment on flexible PET substrates, the ITO film with a resistivity of 5.6 × 10⁻⁴ Ω cm and average optical transmittance of 84.1% in the visible region are obtained. The optimal ITO surface treated by detergent for 5 min and then by UV ozone for 20 min exhibits the best WF value of 5.22 eV. This improves about 8.30% in the WF compared with that of the untreated ITO film. In the case of optimal treatment with the organic photovoltaic device, meanwhile, 36.6% enhancement in short circuit current density (J_sc) and 92.7% enhancement in conversion efficiency (η) over the untreated solar cell are obtained.     

ITO: Zr bi-layers deposited by reactive O2 and Ar plasma with high work function for silicon heterojunction solar cells

We report the influence of reactive oxygen (O₂) and argon (Ar) plasma based ITO:Zr bi-layers for silicon heterojunction (SHJ) solar cells. The purpose of reactive O₂ sputtered ITO:Zr was to improve the Hall mobility and work function while the Ar based ITO:Zr films play an important role to maintain good electrical characteristics. The thickness of reactive O₂ based ITO:Zr films was fixed at 15 nm while Ar based films was varied from 65 to 125 nm, respectively. ITO:Zr bi-layers with the thickness of 15/105 nm deposited by O₂ and Ar plasma, respectively, showed lowest resistivity of 2.358 × 10⁻⁴ Ω cm and high Hall mobility of 39.3 cm²/V · s. All ITO:Zr bi-layers showed an average transmittance of above 80% in the visible wavelength (380–800 nm) region. Work function of ITO:Zr bi-layers was calculated from the X-ray photoelectron spectroscopic (XPS) data. The ITO:Zr work function was enhanced from 5.3 eV to 5.16 eV with the variation of ITO:Zr bi-layers from 15/65 to 15/125 nm, respectively. Front barrier height in SHJ solar cells can be modified by using TCO films with high work function. The SHJ solar cells were fabricated by employing the ITO:Zr bi-layer as front anti-reflection coating. The SHJ solar cells fabricated on ITO:Zr bi-layer with the thickness of 15/105 nm showed the best photo-voltage parameters as; V_oc = 739 mV, J_sc = 39.12 mA/cm², FF = 75.97%, η = 21.96%.     

ITO材料在减反射膜设计中的应用

改变ITO材料通常作为透明导电膜单独使用的状况,将其作为减反射膜系中的一层,能够在很大程度上增加ITO透明导电膜在可见光部分的透过率.通过使用将ITO材料置于膜系的内层和最外层两类不同的设计思想,可以使ITO透明导电膜达到相当优良的应用效果.使用低压反应离子镀方法制备了设计的两类减反射膜系,实验证明,膜层在可见光部分的透过率显著提高,剩余反射率明显下降,并得到了平均透过率为95.83%,最高透过率达到97.26%,方块电阻为13.2～24.6Ω/□的试验结果.     

低压反应离子镀方法制备ITO透明导电膜

溅射镀膜方法是制备ITO透明导电膜最常用也是实验研究最多的方法。实验使用一种不同于溅射方法的另一种制备工艺—低压反应离子镀方法—制备ITO透明导电膜。实验对不同沉积速率和不同氧气流量对ITO透明导电膜的方块电阻以及光学透过率的影响进行了详细地分析,并综合比较得到了当沉积速率为0.5nm/s,氧气流量为24cm3/min时,在波长为550nm处,方块电阻为20Ω,λ=550nm透过率为90.8%的优质ITO透明导电膜。     

Coulomb Screening and Plasmon Excitation in Graphene at Finite Temperature

By using the random phase approximation (RPA) in many-body perturbation theory, we calculate the polarization function of the electron gas in graphene at finite temperature. Based on this, we calculate the temperature dependent dielectric function ε(q). The thermal effect on ε(q) in various q regions is discussed. The temperature dependence is found to be quadratic. We also investigate the plasmon dispersion relation at finite temperature, with the zero-temperature relation as a special case. The result is in good agreement with recent experimental data.     

ITO的表面处理对有机电致发光器件性能的影响

作为有机电致发光器件(OLEDs)的一个主要部分,ITO的表面形貌以及表面性能对整个器件的性能起着决定性的作用。介绍了对ITO的各种处理方法,包括O2Plasma和UV ozone等。这些方法可以改变ITO的表面化学成分以及结构,可以大幅度地提高器件的亮度、寿命以及稳定性,使OLEDs的实用化成为可能。     

On Superconductivity State in Pure Graphene

We study theoretically the possibility of superconductivity state in pure graphene within the extended attractive Hubbard model. In the absence of disorder, when we use the local attractive interaction potential, U≌5t, where t is hopping term, pure graphene can be in superconductivity state.     

On Superconductivity State in Pure Graphene

We study theoretically the possibility of superconductivity state in pure graphene within the extended attractive Hubbard model. In the absence of disorder, when we use the local attractive interaction potential, U ≌ 5t, where t is hopping term, pure graphene can be in superconductivity state.     

Reduction of guided waves in ITO/glass interface of white organic light emitting diodes (WOLEDs): Layer optimization

In this paper, our main purpose is to reduce Total Internal Reflection (TIR) phenomenon that is happening at Indium Tin Oxide (ITO, n_ito = 1.8 + 0.01i) and Glass (n_glass = 1.51) interface in WOLED to achieve higher output power. In normal WOLED because of higher refractive index contrast between ITO and Glass, guided waves usually limited into ITO layer and approximately 50% of generated light is trapped into ITO layer. Here, we tried to reduce this portion of trapped light by using 12-fold quasi-photonic crystal in mentioned interface. With some gentle changes in 12-folds structure, we could reduce TIR in this interface to less than 9%. Also, far field results before and after adding the structure were studied, which represents success of this idea and will open a new insight to lightning applications.     

Graphene as Gas Sensors

The triatomic and tetratomic gas molecule adsorption effects on the electrical conductivity of graphene are investigated by the tight-binding model, Green's function method, and coherent potential approximation. We find that the electrical conductivity of graphene sheet is sensitive to the adsorption of these gases.     

Reactivity at the oxygen/titania interface and the related charge transfer

The present paper reports the reactivity between TiO₂ and oxygen and the related charge transfer at 298 and 1,073 K. The studies were performed using work function measurements. It was found that oxidation of TiO₂ at 1,073 K and p(O₂) = 75 kPa, initially standardized at 1,173 K and p(O₂) = 10 Pa, results in work function changes that are consistent with the theoretical model of the charge transfer during oxygen chemisorption and oxygen incorporation at the absence of structural transitions. However, oxidation of TiO₂ at 298 K, p(O₂) = 75 kPa, which has been initially standardized at 1,173 K in extremely reducing conditions at p(O₂) = ∼10⁻¹⁰ Pa, results in work function changes that are consistent with low-dimensional structural changes of the surface layer. It is shown that oxidation of strongly reduced TiO₂ at 298 K results in a decrease of work function, which cannot be explained without assuming the structural changes of the outermost surface layer.     

Layer optimization in wight organic light emitting diodes (WOLEDs) to reduce the portion of guided waves in ITO/Glass interface

In this paper, our main attempt was to reduce Total Internal Reflection (TIR) happening at Indium Tin Oxide (ITO, n_ito = 1.8 + 0.01i) and Glass (n_glass = 1.51) interface, which is due to ITO's higher index in comparison with Glass's, that makes light guided in ITO layer, 50% of generated light in Wight Organic Light Emitting Diodes (WOLED) are trapped in ITO layer; here we tried to reduce this portion of trapped light by implying 12-fold quasi-photonic crystal to the mentioned interface. With some gentle changes in 12-fold's structure we could reduce TIR in this interface to less than 9%. Also, far field results before and after adding the structure to WOLED were studied, which represents suitability of using this structure for lighting applications.     

Transparent conducting indium-tin-oxide (ITO) film as full front electrode in III-V compound solar cell

The application of transparent conducting indium-tin-oxide (ITO) film as full front electrode replacing the conventional bus-bar metal electrode in III-V compound GaInP solar cell was proposed. A high-quality, non-rectifying contact between ITO and 10 nm N⁺-GaAs contact layer was formed, which is benefiting from a high carrier concentration of the terrilium-doped N⁺-GaAs layer, up to 2×10¹⁹ cm^-3. A good device performance of the GaInP solar cell with the ITO electrode was observed. This result indicates a great potential of transparent conducting films in the future fabrication of larger area flexible III-V solar cell.     

用于彩色滤光片的低阻低应力ITO透明导电膜

探讨了用于彩色滤光片的低电阻和低压应力的ITO透明导电膜工艺。用磁控溅射方法在不同温度的衬底上制备了ITO薄膜。研究了膜形衬底温度与膜结晶化程度的关系,以及膜形衬底温度对膜电阻和压应力的影响。对不同衬底温度下形成的ITO薄膜进行了退火处理,并对退火后的ITO薄膜的电阻和压应力特性进行了分析。结果表明,采用室温沉积非晶态ITO膜,在真空退火下可获得低电阻、低压应力的多晶相ITO膜。     

Characteristic difference between ITO/ZrCu and ITO/Ag bi-layer films as transparent electrodes deposited on PET substrate

The metallic-glass film of ZrCu layer deposited by co-sputtering was utilized as the metallic layer in the bi-layer structure transparent conductive electrode of ITO/ZrCu (IZC) deposited on the PET substrate using magnetron sputtering at room temperature. In addition, the pure Ag metal layer was applied in the same structure of transparent conductive film, ITO/Ag, in comparison with the IZC film. The ZrCu layer could form a continuous and smooth film in thickness lower than 6 nm, compared with the island structure of pure Ag layer of the same thickness. The 30 nm ITO/3 nm ZrCu films could show the optical transmittance of 73% at 550 nm wavelength. The 30 nm ITO/12 nm ZrCu films could show the better sheet resistance of 20 Ω/sq, but it was still worse than that of the ITO/Ag films. It was suggested that an alloy system with lower resistivity and negative mixing heat between atoms might be another way to form a continuous layer in thickness lower than 6 nm for metal film.     

Thin film hexagonal gold grids as transparent conducting electrodes in organic light emitting diodes

Indium Tin Oxide (ITO) coated glass is currently the preferred transparent conducting electrode (TCE) for organic light emitting diodes (OLEDs). However, ITO has its drawbacks, not least the scarcity of Indium, high processing temperatures, and inflexibility. A number of technologies have been put forward as replacements for ITO. In this paper, an OLED based on a gold grid TCE is demonstrated, the light emission through the grid is examined, and luminance and current measurements are reported. The gold grid has a sheet resistance of 15 Ω□⁻¹ and a light transmission of 63% at 550 nm, comparable to ITO, but with advantages in terms of processing conditions and cost. The gold grid OLED has a lower turn‐on voltage (7.7 V versus 9.8 V) and achieves a luminance of 100 cdm⁻² at a lower voltage (10.9 V versus 12.4 V) than the reference ITO OLED. We discuss the lower turn‐on voltage and the uniformity of the light output through the gold grid TCE and examine the conduction mechanisms in the ITO and gold grid TCE OLEDs.     

AlGaInP thin-film LED with omni-directionally reflector and ITO transparent conducting n-type contact

In this paper a novel A1GalnP thin-film light-emitting diode （LED） with omni-directionally reflector （ODR） and transparent conducting indium tin oxide （ITO） n-type contact structure is proposed, and fabrication process is developed. This reflector is realized with the combination of a low-refractive-index dielectric layer and a high reflectivity metal layer. This allows the light emitted or internally reflected downwardly towards the GaAs substrate at any angle of incidence to be reflected towards the top surface of the chip. ITO n-type contact is used for anti-reflection and current spreading layers on the ODR-LED with ITO. The sheet resistance of the ITO films （95 nm） deposited on n- ohmic contact of ODR-LED is of the order 23.5Ω/△ with up to 90% transmittance （above 92% for 590-770 nm） in the visible region of the spectrum. The optical and electrical characteristics of the ODR-LED with ITO are presented and compared to conventional AS-LED and ODR-LED without ITO. It is shown that the light output from the ODR-LED with ITO at forward current 20mA exceeds that of AS-LED and ODR-LED without ITO by about a factor of 1.63 and 0.16, respectively. A favourable luminous intensity of 218.3 mcd from the ODR-LED with ITO （peak wavelength 620 nm） could be obtained under 20 mA injection, which is 2.63 times and 1.21 times higher than that of AS-LED and ODR-LED without ITO, respectively.[第一段]     

Electrodeposition of aligned ZnO sheet array on ITO substrate and their field emission characteristics

ZnO sheet array was fabricated by a simple electrodeposition method on the transparent ITO substrate at a temperature of about 60℃. The field emission properties of the ZnO sheet array were investigated. The fluctuation of the field emission current is less than 5% over several hours. The Fowler Nordheim curves with a roughly linear characteristic were obtained by analysing the current density and the intensity of the electrical field. The results prove that such a simple electrochemical method can potentially meet the demands on the production of cold cathodes for field emission display.[第一段]     

Effects of electron beam irradiation on the friction and work function of the wrinkled graphene

The ability to control the tribological and electrical properties of graphene is critical to the fabrication of micro- and nanoelectromechanical systems (MEMS/NEMS) devices. Due to its high energy, electron beam irradiation has been widely used to adjust the local electrical properties of the graphene, such as inducing local defects or n-type doping. However, whether electron beam irradiation can affect the local tribological properties of wrinkled graphene has not been investigated yet. In this research, we demonstrated that the lateral force signal and the work function of the wrinkled monolayer graphene were affected by the electron beam irradiation.By using Kelvin-probe force microscopy (KPFM) and Raman spectroscopy, we measured the local electrical properties of the wrinkled monolayer graphene and confirmed that the electron-beam exposed area was changed as n-doped graphene. We compared the lateral force signal with surface potential data and concluded that the n-type doping induced by electron beam affected the tribological characteristics. Characterization of the electron-beam exposed wrinkled graphene provides a physical insight that the electrical and tribological characteristics of wrinkled graphene are correlated.     

Analysis of defect mode in a dielectric photonic crystal containing ITO defect

In this work, based on the use of ITO as a defect, we study the infrared defect mode in defective photonic crystal made of SiO₂ and InP. Due to the dispersion in the dielectric function of ITO, it is found that the defect mode is sensitive to the ITO thickness. The defect frequency is shown to be blue-shifted as the thickness of ITO decreases. In the angular dependence of defect mode, it is seen that the defect frequency is also blue-shifted when the angle of incidence increases for both TE and TM polarizations. However, the shifting feature is appeared to be nearly polarization-independent. The shift in the defect frequency enables us to employ ITO as a tunable agent in order to design a tunable photonic crystal filter in the infrared region.