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Light-Emitting Devices Based on Direct Band Gap Semiconductor Nanoparticles
Published in Claudia Altavilla, Enrico Ciliberto, Inorganic Nanoparticles: Synthesis, Applications, and Perspectives, 2017
Ekaterina Neshataeva, Tilmar Kümmell, Gerd Bacher
The typical structure of the NP-LEDs operated under DC was adopted from the OLED technology. Usually, a transparent conductive oxide (TCO)-coated glass is used as a substrate and as a transparent electrode. The most frequently used TCO is indium-doped tin oxide (ITO), utilized in touch screens and liquid crystal displays as a standard. An alternative is flourine-doped tin oxide (FTO), frequently used in solar-energy conversion applications (Bach et al. 1998) because of its stable mechanical and chemical properties (Vossen 1977; Chopra et al. 1983). Recent developments show new substitutes for ITO like aluminum- and gallium-doped zinc oxides (Raniero et al. 2006; Minami 2008a,b) and many others. The other electrode typically consists of metals with a low work function. When using barium (Ba), magnesium (Mg), or calcium (Ca), an additional layer of aluminum (Al) or silver (Ag) on top is needed to passivate the reactive electrode and to protect it from oxidation. Because of its easy handling, Al electrodes are most frequently implemented. The active light-emitting layer consisting of either pure nanoparticles or organic/nanoparticle compounds is sandwiched between both the electrodes. While biased in forward direction, holes are supposed to be injected into the active layer from the TCO and electrons from the top metallic electrode, subsequently recombine and emit light. This is the reason why usually a TCO with a high work function and a cathode metal with a low work function value are preferred to lower the energy barriers for hole and electron injection, respectively.
Transparent Electrode for OLEDs
Published in Zhigang Rick Li, Organic Light-Emitting Materials and Devices, 2017
The thin films of transparent conducting oxides (TCOs) have widespread applications owing to their unique properties of good electric conductivity and high optical transparency in the visible spectrum range. There has been a great deal of activities in the development of TCOs for a variety of applications. In general, properly doped oxide materials, e.g., ZnO, SnO2, and In2O3, are used individually or in separate layers, or as mixtures such as indium–tin oxide (ITO) and indium–zinc oxide (IZO) for making TCO thin films. ITO, aluminum-doped ZnO (AZO), and fluorine-doped SnO2 (FTO) are commonly used TCO materials for different applications. The distinctive characteristics of these TCOs have been widely used in antistatic coatings, heat mirrors, solar cells [1,2], flat-panel displays [3], sensors [4], and organic light-emitting diodes (OLEDs) [5–7]. The properties of TCO films are often optimized accordingly to meet the requirements in the various applications that involve TCO. A light-scattering effect due to the use of textured TCO substrates helps enhance light absorbance in thin-film amorphous silicon solar cells [8,9]. However, a rough TCO surface is detrimental for OLED applications. The localized high electric fields induced by the rough TCO surface can cause a nonuniform current flow, leading to dark spot formation or a short device operation lifetime.
Photovoltaics
Published in Sheila Devasahayam, Kim Dowling, Manoj K. Mahapatra, Sustainability in the Mineral and Energy Sectors, 2016
Venkata Manthina, Alexander Agrios, Shahzada Ahmad
The first TCO thin film was deposited over 108 years ago by Badeker (Bädeker, 1907; Philipps, 2015), who deposited CdO with a vapor deposition system. The most commonly used TCOs in solar cells today are based on tin oxide or zinc oxide. They include indium tin oxide (ITO), aluminum-doped zinc oxide (AZO), boron-doped zinc oxide (ZnO:B or BZO) and fluorinated tin oxide (FTO). Critical criteria for TCO materials are electrical conductivity, optical transparency, stability, and cost. There is a trade-off between the first two criteria as more free carriers conduct current better but tend to absorb some visible light. Many TCO materials have good stability over time, but they differ in the processing temperatures they can withstand before conductivity is degraded. ITO offers the best combination of transparency and conductivity and is therefore the most widely used TCO, despite its relatively high cost due to the indium content (Table 24.1).
The influences of the front work function and intrinsic bilayer (i1, i2) on p-i-n based amorphous silicon solar cell’s performances: A numerical study
Published in Cogent Engineering, 2022
Dadan Hamdani, Soni Prayogi, Yoyok Cahyono, Gatut Yudoyono, Darminto Darminto
The energy band offset between semiconductor and TCO ought to be minimized, in order to improve ohmic contact. Therefore, inserted transparent conductive oxides (for instance, Indium Tin Oxide, ITO) with high conductivity (σ > 103 S/cm), good transparency in the visible range (T > 90 %), and higher work function values are required for the higher possibility to carrier injection into TCO/(p)a-Si:H interface. For thin film solar cells, a work function of TCO associated with carrier injection into TCO/(p)-window interface which influences plays a dominant role in the device parameters such as VOC and FF (Oh et al., 2012; Rached & Mostefaoui, 2008). The deposition of ITO films on Corning 1737 substrate, using RF-Magnetron Sputtering method improved ITO work function from 4.67 to 5.66 eV, by the O2 plasma treatment and an almost stable resistivity (J. Park et al., 2013). Meanwhile, the electrical and optical characteristics of the ITO films are improved by doping the films with high permittivity materials (Zr, ZrO2), and this results in high mobility and work functions due to the excellent surface (Hussain et al., 2014; Khokhar et al., 2020; Zhang, 2010). Furthermore, optical losses in TCO were reduced without compromising with Rs and recombination loss, using ITO/SiOx stacks, to produce the short circuit current density (JSC) > 41.3 mA/cm2, with a 100 Ω sheet resistance, while ITO/SiNx/SiOx produced a 42 mA/cm2JSC, with a 300 Ω sheet resistance (Herasimenka et al., 2016). Cruz et al., also reported the effect of various TCO (ITO, ZnO:Al, IO:H) as rear-junction of the silicon heterojunction solar cells, through experiments and simulation (Cruz et al., 2019).
Liquid crystal aligning capabilities on surface-reformed indium-doped zinc oxide films via ion-beam exposure
Published in Liquid Crystals, 2018
Ju Hwan Lee, Eun-Mi Kim, Gi-Seok Heo, Hae-Chang Jeong, Dong Hyun Kim, Dong Wook Lee, Jeong-Min Han, Tae Wan Kim, Dae-Shik Seo
A deposition method is required in order to use TCO materials as a thin film. In:ZnO film can be deposited by various ways, such as sputtering [14,15], chemical vapour deposition [16], and atomic layer deposition [17]. However, these techniques need complicated facilities and are associated with high costs. In contrast, using solution processing as a deposition method has various ad vantages, such as cost-effectiveness, simple facilities, easy-to-control molality, and high reliability and stability [18,19].
Environmental assessment of transparent conductive oxide-free efficient flexible organo-lead halide perovskite solar cell
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2021
Huseyin Sarialtin, Roland Geyer, Ceylan Zafer
Major features of a transparent conducting oxide (TCO) layer deposited on a glass substrate are a metal-like transmission capability, appropriate work function, and the ability to transmit photons into a cell with a wide range of wavelengths (Minami 2005). Two commonly used TCO materials are Indium Tin Oxide (ITO) and Fluorine Tin Oxide (FTO) (Xie et al. 2017; Zhao et al. 2017). Researches have shown that ITO has several advantages in respect of ohmic behavior and conductivity (Chander et al. 2017; Purohit et al. 2017). On the other side, FTO is generally preferred in thin film solar cell fabrication because of crystallinity and electrical conductivity performances (Chander and Dhaka 2017a, 2017b), price advantage (Michael 2012) and avoidance of the critical metal Indium, which is commonly used in thin film applications (Department of Energy 2018). On the other hand, it is shown that TCO substrates can cause transmission loss in PSC device (Hu et al. 2017). Previous life cycle assessment studies also have shown that TCO coated glass has the highest portion of electricity consumption in the perovskite solar cell manufacturing process (Espinosa et al. 2015; Sarialtin, Geyer, and Zafer 2020; Serrano-Lujan et al. 2015). Considering that the amount of electricity required for manufacturing PSCs is the largest factor in determining their environmental profile (Espinosa et al. 2015), it is important to investigate device architectures with the elimination of this layer. Flexible substrate applications such as Polyethylene terephthalate (PET) are suitable for PSCs because it allows the device to be more lightweight and bendable compared to glass or other rigid substrates (Dou et al. 2017; Popoola, Gondal, and Qahtan 2018). It was shown that the production temperatures of organic-inorganic CH3NH3PbI3 perovskite technologies can be controlled to be in the range of 100–150°C (Heo et al. 2013) and the flexibility (Poisson’s ratio) of the perovskite material is suitable for flexible production (Feng 2014).