Thin films of molecular organic materials

CuInS2 (CIS) thin films are prepared by the successive ionic layer adsorption and reaction method (SILAR) by single cationic route under two different conditions (without stirring and with stirring). The effect of stirring on the structural, optical, compositional and morphological properties of the prepared Cu-rich CuInS2 thin films has been studied and reported in this paper. Full Text: PDF References M.Krunks, A.Mere, A.Katerski, V.Mikli and J.Krustok, "Characterization of sprayed CuInS2 films annealed in hydrogen sulfide atmosphere", Thin Solid Films 511-512, 434 (2006).CrossRef S.K.Kim, W.J.Jeong, G.C.Park, Y.G.Back, Y.G.Jeong and Y.T.Yoo, "Heat-treatment effect of chalcopyrite copper indium disulphide thin film growth", Synthetic Metals 71, 1747 (1995).CrossRef Roland Scheer, Progress in photovoltaics: Research and Applications, "Open questions after 20 years of CuInS2 research", (2012).CrossRef M.Krunks, O.Kijatkina, H.Renace, I.Oja, V.Mikli and A.Mere, "Composition of CuInS2 thin films prepared by spray pyrolysis", Thin Solid Films 403-404, 71 (2002).CrossRef Y.B.He, T.Kramer, I.Osterreicher, A.polity, R.Gregor, W. Krieg seis, D.Hasselkamp and B.K.Meyer, "Highly (112)-Oriented CuInS2 Thin Films Deposited by a One-Stage RF Reactive Sputtering Process", Jpn.J.Appl.Phys. 41, L484 (2002).CrossRef J.Qiu, Z.Jin, J.Qian, Y.Shi and W.Wu, "ILGAR CuInS2 films from various preparation conditions", Mater. Lett. 59, 2735 (2005).CrossRef N.Suriyanarayanan and C.Mahendran, "EDAX, SEM, Photoluminescence and Electrical properties of Zn- doped polycrystalline CuInS2 Thin films by spray pyrolysis", Archives of Physics Research 3 (1), 54 (2012).DirectLink Y.Pena, S.Lugo, M.C.Rodriguez, A.Vazquez, I.Gomez and P.Elizo nodo, "CuInS2 thin films obtained through the annealing of chemically deposited In2S3?CuS thin films", Appl.Surf. Sci. 257, 2193 (2011).CrossRef A.B.Mandale, S.D.Sathaye and K.R.Patil, "Preparation of Q-copper indium sulfide thin films by liquid?liquid interface reaction technique (LLIRT)", Mater. Lett. 55, 30 (2002).CrossRef M.Ben Rabeh, N.Chaglabou and M.Kanzari, "Effect of Antimony Incorporation in CuInS2 Thin Films", Chalcogenide Lett. 6 (4),155 (2009).CrossRef Y.B.He, A.Polity, R.Gregor, D.Pfisterer, I.Osterreicher, D.Hasse lkamp and B.K.Meyer, "Characterization of RF reactively sputtered Cu?In?S thin films", Physics B. 308-310, 1074 (2001).CrossRef K.Zeaiter, Y.Llinares and C.Llinares, "Structural and photoluminescence study of the quaternary alloys system CuIn(SxSe1?x)2", Sol. Energy Mater. Sol. Cells 61, 313 (2000).CrossRef A.Antony, A.S.Asha, R.Yoosuf, R.Manoj and M.K.Jayaraj, "Growth of CuInS2 thin films by sulphurisation of Cu?In alloys", Sol. Energy Mater. Sol. Cells 81, 407 (2004)CrossRef Y.Shi, Z.Jin, C.Li, H.An and J.Qiu, "Effect of [Cu]/[In] ratio on properties of CuInS2 thin films prepared by successive ionic layer absorption and reaction method", Appl. Surf. Sci. 252, 3737 (2006).CrossRef S.J.Roh, R.SMane, H.Pathan, O.S.Joo and S.H.Han, "Rapid growth of nanocrystalline CuInS2 thin films in alkaline medium at room temperature", Appl. Surf. Sci. 252, 1981 (2005).CrossRef Gray Hodes, Chemical Solution Deposition of Semiconductor Films (Marcel Dekker, Inc, pp-131).DirectLink R.P.Wijesundera and W.Siripala, "Preparation of CuInS2 thin films by electrodeposition and sulphurisation for applications in solar cells", Sol. Energy Mater. Sol. Cells 81, 147 (2004).CrossRef C.Guillen, J.Herrero, M.T.Gutierrez and F.Briones, "Structure, morphology and optical properties of CuInS2 thin films prepared by modulated flux deposition", Thin solid films 480- 481, 19 (2005). DirectLink P.Guha, S.Gorai, D.Ganguli and S.Chanudhuri, "Ammonia-mediated wet chemical synthesis of CuInS2"Mater. Lett. 57, 1786 (2003).CrossRef Y.B.He. T.Kramer, I.Osterreicher, A.Polity, B.K.Meyer and M.Hardt, "Post-growth treatment effects on properties of CuInS2 thin films deposited by RF reactive sputtering", Semicond. Sci.Technol. 20, 685 (2005).CrossRef S.Aksay and B.Altiokka, "Effect of substrate temperature on some of the optical parameters of CuInS2 films", Physica Status Solidi (c) 4, 585-588, No.2 (2007)CrossRef N.M.Ravindra, Preethi Ganapathy, Jinsoo Choi, "Energy gap?refractive index relations in semiconductors ? An overview", Infrared Physics and Technology, 50, 1 21 (2007)CrossRef

Sputtered transparent electrodes for optoelectronic devices: Induced damage and mitigation strategies

Currently, the flexible organic light emitting devices (OLEDs) are investigated. They are very vulnerable to moisture, and thus have been found to show some problems. Thus, an effective barrier layer is needed to protect from moisture in air. We deposited thin films with magnesium oxide (MgO) and silicon oxide (SiO2) compounds mixed at various mixture ratios on flexible polyether sulfone (PES) substrates by an electron‐beam evaporator to investigate their applizability for transparent barrier applications. In this study, we found that as the MgO fraction increased, thin films comprised of MgO and SiO2 compounds became more amorphous and their surface morphologies become smoother and denser. In addition, zirconium oxide (ZrO2) was added to the above‐mentioned compound mixtures. ZrO2 made thin mixture films more amorphous and made the surface morphology denser and more uniform. The water vapor transmission rates (WVTRs) of the whole films decreased rapidly. The best WVTR was obtained by depositing thin films of Mg‐Si‐Zr‐O compound among the whole thin films. As the thin mixture films became more amorphous, and the surface morphology become denser and more uniform, the WVTRs decreased. Therefore, the thin mixture films became more suitable for flexible OLED applications as transparent passivation layers against moisture in air.

Organisation, structure and morphology of organic thin films via electron microscopy

The aim of the research was to modify the surface of construction textiles by means of the use of thin silver oxide films, investigate the structure and optical and mechanical properties, and determine the structure, optical and mechanical properties of the aged composites. Thin films of silver oxide (Ag2O) were synthesized on a flexible PET/PVC construction textile (CT); the structural, optical, and physical properties, as well as the effect of artificial aging on these properties, were investigated. The SILAR method (successive ionic layer adsorption and reaction) was used to synthesize thin Ag2O films on the CT surface. Before the thin films were deposited, the CT surface was mechanically roughened and pretreated with acidic and alkaline solutions at an elevated temperature. XRD analysis showed that the deposited films were a polycrystalline mixed phase material consisting of Ag2O, AgO, and metallic Ag. Diffuse reflectance spectra in the ultraviolet and visible ranges (UV-Vis) were used to study the optical properties of the deposited thin films. The synthesized Ag2O/CT composites were direct-gap semiconductors (the optical band gap (Eg) was 0.89 ± 0.02 eV). Eg and refractive indices (n) increased as the aging tests were carried out. Higher Eg and n meant that the composites were a good material for optoelectronic applications. The results showed that, after modification, the structural properties and tear strength of the PET/PVC fabric remained the same while the tensile strength decreased. The same tendencies remained after artificial aging.

Biomolecular DNA, as a marine waste product from salmon processing, has been exploited as biodegradable polymeric material for photonics and electronics. For preparing high optical quality thin films of DNA, a method using DNA with cationic surfactants such as DNA–cetyltrimethylammonium, CTMA has been applied. This process enhances solubility and processing for thin film fabrication. These DNA–CTMA complexes resulted in the formation of self-assembled supramolecular films. Additionally, the molecular weight can be tailored to suit the application through sonication. It revealed that DNA–CTMA complexes were thermostable up to 230∘ C. UV–VIS absorption shows that these thin films have high transparency from 350 to about 1,700 nm. Due to its nature of large band gap and large dielectric constant, thin films of DNA–CTMA has been successfully used in multiple applications such as organic light emitting diodes (OLED), a cladding and host material in nonlinear optical devices, and organic field-effect transistors (OFET). Using this DNA based biopolymers as a gate dielectric layer, OFET devices were fabricated that exhibits current–voltage characteristics with low voltages as compared with using other polymer-based dielectrics. Using a thin film of DNA–CTMA based biopolymer as the gate insulator and pentacene as the organic semiconductor, we have demonstrated a bio-organic FET or BioFET in which the current was modulated over three orders of magnitude using gate voltages less than 10 V. Given the possibility to functionalise the DNA film customised for specific purposes viz. biosensing, DNA–CTMA with its unique structural, optical and electronic properties results in many applications that are extremely interesting.

Organic light-emitting diodes (OLEDs) have reached a huge market as technology for small displays, e.g. in smartphones, and are entering the larger display and solid-state lighting markets as well. In parallel to these commercial successes, the OLED technology is adapted to a multitude of promising new applications, such as in optogenetics and medical therapy. However, it is still challenging to ensure good stability in applications that require high brightness (or high optical power density), in part due to the resulting resistive heating. Increased temperature can lead to a change in morphology of one or several organic layers, e.g. via crystallization of organic molecules, which then reduces electrical and optical performance and likely results in rapid device failure. Aside from an intrinsic resistive heating, heating can also be due to environmental effects during operation or fabrication and encapsulation of devices. For instance, atomic layer deposition (ALD) is a promising technique to form thin, yet highly protective encapsulation layers. However, state-of-the-art ALD processes require relatively high temperature during deposition (< 80 °C). 4,7-diphenyl-1,10-phenanthroline (BPhen) has been widely used as electron transporting layer (ETL) due its high electron mobility, particularly in an organic matrix-dopant system. However, it is well known that thin films of BPhen tend to recrystallize spontaneously. Annealing accelerates crystallization even further due to the relatively low glass transition temperature (Tg) of BPhen (62 °C). A straightforward way to enhance the device thermal stability is to make use of a high Tg material, yet materials have to be carefully adopted to provide appropriate functionality in OLEDs. In this contribution, we report the improvement of the thermal stability of OLEDs with BPhen based electron transport layers (ETLs) by cesium (Cs) doping. To verify the role of the Cs dopant in the BPhen matrix, recrystallization features of Cs-doped BPhen films with different doping concentrations were investigated using optical microscopy and atomic force microscopy. We also examined the photophysical properties of the films, i.e. photoluminescence (PL) and absorption. PL spectra exhibit monotonic red-shifts and broadening as the Cs doping concentration increases. This presumably indicates formation of metal complexes via interaction between the 1,10-phenanthroline group of BPhen molecules and the Cs ions. It was found that Cs plays a critical role, not only in inhibiting undesired recrystallization of BPhen molecules in a thin-film, but also in allowing BPhen layers to be thermally stable beyond the Tg of neat BPhen. Next, the electrical and optical properties of blue and red OLEDs that contain BPhen layers with different Cs-doping concentrations as ETL were characterized after annealing at temperatures between 60 and 100 °C. We find that higher doping concentrations lead to a marked increase in thermal device stability (quantified by current density and luminance at a fixed voltage). Making use of this observation, we successfully encapsulated BPhen based OLEDs with thin-film oxide layers using ALD. The results shown in this work may be transferable to other material systems and can thus provide a useful guideline to enhance the intrinsic thermal durability of organic devices and to render them compatible with processes involving thermal treatment.

On the conductivity of PEDOT:PSS thin films

Room temperature solution processing of highly compact, glass-like thin films of ZnO, SnO2 and Zn-Sn oxide was achieved for the purpose to use them as thin film encapsulation (TFE) for flexible film organic light emitting diodes (OLEDs), by employing photochemical decomposition of metalorganic precursors under vacuum ultraviolet (VUV) irradiation. Care had to be taken to control the amount of water in the coating solution since hydration water in the precursor compound already gave a strong influence to promote granular crystal growth. With anhydrous precursors, highly flat thin films without pinholes and cracks could be obtained. The analysis by FTIR and ellipsometry revealed fast decomposition of organic ligand and polycondensation to metal oxide thin films with high densities within 5 minutes. TEM observation in fact revealed crystallization into ZnO in about 5 nm size, despite the reaction was carried out in the absence of water and under N2. Since the process does not require a high temperature, O2 condition and H2O to harm OLED devices, these metal oxides could be applied to OLEDs as TFEs to extend their lifetime for 3-4 times.

In this work, circular economy was investigated for commercial indium tin oxide (ITO) thin films deposited on glass substrates obtained from degraded organic light-emitting diodes (OLED). These devices were assembled and polarized at laboratory in a previous work. For each substrate, with geometry 2.5 × 2.5 cm, four OLEDs with active area of 3 × 3 mm were set up. These OLED devices were assembled with ITO as the electrode anode and successive depositions of other materials (layer-by-layer), to form the complete structure. To obtain the recovered ITO, all layers were removed from the samples containing the OLEDs previously mounted, remaining only the ITO thin films, that were cleaned with commercial product together with the received ITO/glass samples. Both samples were compared using some techniques, such as: colorimetry, electrical resistance, and Raman spectroscopy. A methodology with light-emitting diode (LED) device polarized emitting light crossing the ITO thin films was used, and the luminance with chromaticity coordinates was obtained, revealing the good transparency of the thin films. Electrical resistance of recovered ITO revealed five higher orders of magnitude in comparison to the one of received ITO. This fact can be tributed to a poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate) (PEDOT:PSS) layer, causing corrosion of the ITO thin films during the assembly of OLEDs or loss of the field lines created during the electrical measurements by probes of four-point probe. Raman spectroscopy did not show satisfactory results in the chemical composition analyses of the samples, but it indicated good cleaning process of the samples before the analyses.

Thin films of amorphous Ga2S3 and rare-earth sulphides

Modeling of bias-induced changes of organic field-effect transistor characteristics

Preparation and properties of thermistor thin-films by metal organic decomposition

Development of a new diindenopyrazine–benzotriazole copolymer for multifunctional application in organic field-effect transistors, polymer solar cells and light-emitting diodes

Pentacene organic thin-film transistors (OTFTs) have demonstrated the highest performance among TFTs with an organic semiconductor channel. High operating voltages (20-100 V), stemming from poor capacitive coupling between gate electrode and channel, are a major limitation, particularly for portable battery-powered device applications. OTFTs fabricated on flexible polymer substrates, often characterized by rough surfaces, benefit from the use of high-K dielectrics given the ability to accommodate thicker films which ensure the pinhole-free and good coverage without need to increase operating voltage. As we demonstrate, pyrochlore structured thin films can provide the requisite high dielectric constant coupled with excellent leakage current characteristics, while remaining compatible with the processing requirements of flexible OTFTs. The introduction of an extremely thin parylene film between the BZN dielectric and the pentacene semiconductor markedly shifts the threshold voltage, making it possible to fabricate both enhancement (E) and depletion (D) TFTs. We report the successful fabrication of low-voltage (<2 V) organic transistors and depletion-load inverter using a 200-nm-thick pyrochlore gate dielectric, Bi/sub 1.5/Zn/sub 1.0/Nb/sub 1.5/O/sub 7/ (BZN), prepared by a room temperature process. The inverters with depletion load were successfully operated under 5 V with excellent noise margin.