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Crystals
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Advances in Thin Film Materials and Devices
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Advances in Thin Film Materials and Devices

A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Inorganic Crystalline Materials".

Deadline for manuscript submissions: closed (20 July 2020) | Viewed by 52188

Special Issue Editor

Prof. Dr. Sungsik Lee

E-Mail Website
Guest Editor
Department of Electronics, Pusan National University, Busan, Republic of Korea
Interests: organic and inorganic thin-film materials, electronic devices, device physics

Special Issue Information

Dear Colleagues,

Since thin-film materials and devices began to be used for display applications, they have been adapted for other applications, including wearable devices. Thin-film transistors with inorganic materials, for example, are used not only for displays, but also in low-cost wearable circuits and systems. Recently, among inorganic materials, conducting oxides and perovskite have been adapted for various emerging applications, including wearable devices and solar cells. Additionally, following a dramatic improvement in electrical properties, organic material-based transistors are currently feasible for high-performance uses, such as in wide dynamic range solar cells and wearable devices.

To achieve these advancements, intensive research on such materials and devices has been conducted. Materials have been synthesized and made at a fundamental level in multi-scale studies through modeling, fabrications, and experiments to obtain relevant and optimum compositions and phases. Additionally, higher level device technologies capable of sophisticated, macroscopic performances have been developed for such device operations via research utilizing advanced characterizations and modeling. Moreover, many other research breakthroughs have been required to make such advancements.

Here, we invite researchers to submit papers related to thin-film materials and devices to discuss recent advances in fields relating to any thin-film inorganic and organic materials and/or devices.

Prof. Dr. Sungsik Lee
Guest Editor

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Crystals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2100 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Organic materials
  • Inorganic materials
  • Thin-film transistors
  • Thin-film solar cells
  • Material synthesis and deposition
  • Device fabrication
  • Measurements and characterizations
  • Material and device modeling

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Published Papers (11 papers)

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10 pages, 5823 KiB  
Communication
All-Inkjet Printed Organic Thin-Film Transistors with and without Photo-Sensitivity to Visible Lights
by Chen Jiang
Crystals 2020, 10(9), 727; https://doi.org/10.3390/cryst10090727 - 20 Aug 2020
Cited by 12 | Viewed by 3625
Abstract
Printable organic thin-film transistors have enabled flexible low-cost electronics, which has the potential for a lot of emerging electronic applications. Despite the excellent dark performance of advanced all-inkjet printed organic thin-film transistors, their photoresponse is less explored and needs to be investigated, especially [...] Read more.
Printable organic thin-film transistors have enabled flexible low-cost electronics, which has the potential for a lot of emerging electronic applications. Despite the excellent dark performance of advanced all-inkjet printed organic thin-film transistors, their photoresponse is less explored and needs to be investigated, especially photoresponse to visible lights that human beings can see and are most familiar with. Importantly, for electronics integration, both devices with and without photo-sensitivity to visible light are important, for photo-detecting and signal processing, respectively. In this study, two organic semiconductor materials are used in all-inkjet printed organic thin-film transistors, namely 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT), 6,13-bis (triisopropylsilylethynyl) pentacene (TIPS-pentacene). By characterizing devices under optical exposure with wavelengths from 400 to 800 nm, photocurrents and threshold voltage shifts of the devices are extracted. The fabricated C8-BTBT organic thin-film transistors do not exhibit noticeable photo-sensitivity to visible light, whereas the TIPS-pentacene devices demonstrate significant photoresponse to visible lights, with photocurrents in nano- to micro-ampere levels and threshold voltage shifts of hundreds of millivolts to several volts depending on the photon energy of lights under the same intensity. The TIPS-pentacene devices demonstrated reproducible characteristics before and after light exposure. In addition, the responsivity and sensitivity of the devices were characterized with a decent responsivity of 55.9 mA/W. The photoresponse mechanisms are explained with ultraviolet–visible (UV–vis) adsorption spectroscopy measurements and extracted optical bandgaps of the two semiconductors. This study shows both printed organic transistors with and without photo-sensitivity can be fabricated with the same device structure and fabrication process at low cost, which opens the new possibility of using printed organic thin-film transistors for integrated optoelectronic applications. Full article
(This article belongs to the Special Issue Advances in Thin Film Materials and Devices)
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22 pages, 8323 KiB  
Article
Investigation of Structure, Optical, and Electrical Properties of CuS Thin Films by CBD Technique
by Khozik Ahmed Mohammed, Sabah M. Ahmed and Raghad Y. Mohammed
Crystals 2020, 10(8), 684; https://doi.org/10.3390/cryst10080684 - 7 Aug 2020
Cited by 26 | Viewed by 5328
Abstract
Copper Sulfide (CuS) thin films were deposited onto a glass substrate using the Chemical Bath Deposition (CBD) technique. The chemical bath Precursors were made up of CuSO4, SC(NH2)2, and C4H6O6. Different [...] Read more.
Copper Sulfide (CuS) thin films were deposited onto a glass substrate using the Chemical Bath Deposition (CBD) technique. The chemical bath Precursors were made up of CuSO4, SC(NH2)2, and C4H6O6. Different parameters have been considered to specify the optimum conditions for fabricating CuS thin films, such as solution temperature, deposition time, pH level, and different precursor concentrations. It has been found that the optimum deposition time is 20 min at temperature 80 °C and pH = 11. The optimum precursor concentrations were 0.15 M, 0.2 M, and 0.1 M of CuSO4, SC(NH2)2, and C4H6O6, respectively. The structural properties of the thin film were studied using X-ray diffraction (XRD), and a single peak was observed for the thin film made at optimum conditions, while all other cases were amorphous. It is obvious from the optical characterization that the transmission spectra show a red-shift for the cases of increasing deposition time, bath temperature, C4H6O6 concentration, and pH. For the case of increasing CuSO4, blue shifts in the transmission spectra were observed. The energy band gap, resistivity, and activation energy of CuS thin films under optimum conditions are 2.35 eV, 0.7 Ω·cm, and 0.0152 eV, respectively. Full article
(This article belongs to the Special Issue Advances in Thin Film Materials and Devices)
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9 pages, 4806 KiB  
Article
Atomic Layer Deposition of Superconducting CuO Thin Films on Three-Dimensional Substrates
by Aile Tamm, Aivar Tarre, Valeriy Verchenko, Helina Seemen and Raivo Stern
Crystals 2020, 10(8), 650; https://doi.org/10.3390/cryst10080650 - 29 Jul 2020
Cited by 19 | Viewed by 3664
Abstract
In previous decades, investigation of superconductors was aimed either at finding materials with higher critical temperatures or at discovering nontypical superconducting behavior. Here, we present the cupric (CuO) thin films, which were synthesized by atomic layer deposition by using a metal-organic precursor, copper [...] Read more.
In previous decades, investigation of superconductors was aimed either at finding materials with higher critical temperatures or at discovering nontypical superconducting behavior. Here, we present the cupric (CuO) thin films, which were synthesized by atomic layer deposition by using a metal-organic precursor, copper (II)-bis-(-dimethylamino-2-propoxide), and ozone as an oxidizer. The deposition process was optimized by employing a quartz crystal monitoring, and the contact between the deposited films and planar and three-dimensional SiO2/Si substrates was examined by scanning electron microscopy with a focused ion beam module. Phase and elemental composition were analyzed by X-ray diffraction and X-ray fluorescence. Two-probe electrical resistivity measurements revealed a resistivity drop below the critical temperature of 4 K, which may indicate low-temperature superconductivity of the CuO thin films. Full article
(This article belongs to the Special Issue Advances in Thin Film Materials and Devices)
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13 pages, 3793 KiB  
Article
Effects of Thermal Annealing on Optical Properties of Be-Implanted GaN Thin Films by Spectroscopic Ellipsometry
by Wenwang Wei, Jiabin Wang, Yao Liu, Yi Peng, Mudassar Maraj, Biaolin Peng, Yukun Wang and Wenhong Sun
Crystals 2020, 10(6), 439; https://doi.org/10.3390/cryst10060439 - 30 May 2020
Cited by 10 | Viewed by 4224
Abstract
Wide bandgap III-V compounds are the key materials for the fabrication of short-wavelength optical devices and have important applications in optical displays, optical storage devices and optical communication systems. Herein, the variable-angle spectroscopic ellipsometry (SE) measurements are performed to investigate the thickness and [...] Read more.
Wide bandgap III-V compounds are the key materials for the fabrication of short-wavelength optical devices and have important applications in optical displays, optical storage devices and optical communication systems. Herein, the variable-angle spectroscopic ellipsometry (SE) measurements are performed to investigate the thickness and optical properties of beryllium-implanted gallium nitride thin films that have been deposited on (0001) sapphire substrates by using low-pressure metalorganic chemical vapor deposition (LPMOCVD). The film layer details are described by using Parametric Semiconductor oscillators and Gaussian oscillators in the wavelength range of 200–1600 nm. The thickness, refractive indices and extinction coefficients of the Be-implanted films are determined at room temperature. Analysis of the absorption coefficient shows that the optical absorption edge of Be-implanted films changes from 3.328 eV to 3.083 eV in the temperature range of 300–850 K. With the variable temperature, Eg is demonstrated to follow the formula of Varshni. A dual-beam ultraviolet–visible spectrophotometer (UV–VIS) is used to study the crystal quality of samples, indicating that the quality of rapid thermal annealing (RTA) sample is better than that unannealed sample. By transport of ions in matter (TRIM) simulation and SE fitting the depths of Be implanted gallium nitride (GaN) films are estimated and in good agreement. The surface and cross-section morphologies are characterized by atomic force microscopy (AFM) and scanning electron microscope (SEM), respectively. The surface morphologies and thickness measurements of the samples show that RTA can improve crystal quality, while increasing the thickness of the surface roughness layer due to partial surface decomposition in the process of thermal annealing. Full article
(This article belongs to the Special Issue Advances in Thin Film Materials and Devices)
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17 pages, 1706 KiB  
Article
Structural, Optoelectrical, Linear, and Nonlinear Optical Characterizations of Dip-Synthesized Undoped ZnO and Group III Elements (B, Al, Ga, and In)-Doped ZnO Thin Films
by A. M. Alsaad, A. A. Ahmad, I. A. Qattan, Qais M. Al-Bataineh and Zaid Albataineh
Crystals 2020, 10(4), 252; https://doi.org/10.3390/cryst10040252 - 27 Mar 2020
Cited by 75 | Viewed by 6568
Abstract
Undoped ZnO and group III (B, Al, Ga, and In)-doped ZnO thin films at 3% doping concentration level are dip-coated on glass substrates using a sol-gel technique. The optical properties of the as-prepared thin films are investigated using UV–Vis spectrophotometer measurements. Transmittance of [...] Read more.
Undoped ZnO and group III (B, Al, Ga, and In)-doped ZnO thin films at 3% doping concentration level are dip-coated on glass substrates using a sol-gel technique. The optical properties of the as-prepared thin films are investigated using UV–Vis spectrophotometer measurements. Transmittance of all investigated thin films is found to attain high values of ≥80% in the visible region. We found that the index of refraction of undoped ZnO films exhibits values ranging between 1.6 and 2.2 and approximately match that of bulk ZnO. Furthermore, we measure and interpret nonlinear optical parameters and the electrical and optical conductivities of the investigated thin films to obtain a deeper insight from fundamental and practical points of view. In addition, the structural properties of all studied thin film samples are investigated using the XRD technique. In particular, undoped ZnO thin film is found to exhibit a hexagonal structure. Due to the large difference in size of boron and indium compared with that of zinc, doping ZnO thin films with these two elements is expected to cause a phase transition. However, Al-doped ZnO and Ga-doped ZnO thin films preserve the hexagonal phase. Moreover, as boron and indium are introduced in ZnO thin films, the grain size increases. On the other hand, grain size is found to decrease upon doping ZnO with aluminum and gallium. The drastic enhancement of optical properties of annealed dip-synthesized undoped ZnO thin films upon doping with group III metals paves the way to tune these properties in a skillful manner, in order to be used as key candidate materials in the fabrication of modern optoelectronic devices. Full article
(This article belongs to the Special Issue Advances in Thin Film Materials and Devices)
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6 pages, 1354 KiB  
Article
Numerical Analysis of Optical Absorption Effect in Nonhalogen Solution-Processed, Inverted Small Molecule Solar Cell
by Ming-Yi Lin and Chun-Yu Lee
Crystals 2020, 10(2), 113; https://doi.org/10.3390/cryst10020113 - 13 Feb 2020
Cited by 1 | Viewed by 3076
Abstract
Inverted solution-processed SMPV1:PC71BM small molecule organic photovoltaic solar cells (SM-OPVs) were fabricated. The power conversion efficiency (PCE) of halogen-free SM-OPVs reached around 5.07%. The absorption spectra at different device thicknesses were simulated by software Fluxim SETFOS 5.0, and compared with the [...] Read more.
Inverted solution-processed SMPV1:PC71BM small molecule organic photovoltaic solar cells (SM-OPVs) were fabricated. The power conversion efficiency (PCE) of halogen-free SM-OPVs reached around 5.07%. The absorption spectra at different device thicknesses were simulated by software Fluxim SETFOS 5.0, and compared with the experimental results. To further enhance the performance of halogen-free SM-OPVs, the interface between the active layer and the electrode of the optimized device was treated with the solvent vapor annealing (SVA) process, improving the PCE of the inverted halogen-free SM-OPV to 7.21%. Full article
(This article belongs to the Special Issue Advances in Thin Film Materials and Devices)
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14 pages, 5151 KiB  
Article
Effect of Ag/rGO on the Optical Properties of Plasmon-Modified SnO2 Composite and Its Application in Self-Powered UV Photodetector
by James Taban Abdalla, Jinzhong Wang and Dongbo Wang
Crystals 2019, 9(12), 648; https://doi.org/10.3390/cryst9120648 - 6 Dec 2019
Cited by 12 | Viewed by 4835
Abstract
A facile hydrothermal method was employed to synthesize silver–reduced graphene oxide (Ag/rGO) plasmon-modified SnO2 composite, by incorporating Ag–reduced graphene oxide (Ag/rGO) into SnO2 nanorods as a photoanode for assembling a self-powered ultraviolet photodetector (UVPD). The as-synthesized samples were investigated in detail [...] Read more.
A facile hydrothermal method was employed to synthesize silver–reduced graphene oxide (Ag/rGO) plasmon-modified SnO2 composite, by incorporating Ag–reduced graphene oxide (Ag/rGO) into SnO2 nanorods as a photoanode for assembling a self-powered ultraviolet photodetector (UVPD). The as-synthesized samples were investigated in detail by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, and UV visible spectrophotometer. The as-prepared Ag/rGO films show enhanced light absorption attributed to the localized surface plasmon resonance (LSPR). The optimized 1.0 wt.% Ag/rGO incorporated into SnO2-based UVPD exhibits a significant photocurrent response due to the enhanced absorption light and effective suppression of charge recombination. This UVPD demonstrates a high performance, with photocurrent density reaching 0.29 mAcm−2 compared to the SnO2-based device with 0.16 mAcm−2. This device also exhibits a high on:off ratio of 195 and fast response time, which are superior to that of the free-modified one. In addition, the UVPD based on plasmon-modified SnO2 photoanode treated with TiCl4-aqueous solution has attained a higher photocurrent with a maximum value reaching 5.4 mAcm−2, making this device favorable in ultraviolet detection. Full article
(This article belongs to the Special Issue Advances in Thin Film Materials and Devices)
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9 pages, 20671 KiB  
Article
Hysteresis Reduction for Organic Thin Film Transistors with Multiple Stacked Functional Zirconia Polymeric Films
by Jin-Hyuk Kwon, Ji-Hoon Choi, Jin-Hyuk Bae and and Jaehoon Park
Crystals 2019, 9(12), 634; https://doi.org/10.3390/cryst9120634 - 28 Nov 2019
Cited by 8 | Viewed by 3964
Abstract
We show that transfer hysteresis for a pentacene thin film transistor (TFT) with a low-temperature solution-processed zirconia (ZrOx) gate insulator can be remarkably reduced by modifying the ZrOx surface with a thin layer of crosslinked poly(4-vinylphenol) (c-PVP). Pentacene TFTs with [...] Read more.
We show that transfer hysteresis for a pentacene thin film transistor (TFT) with a low-temperature solution-processed zirconia (ZrOx) gate insulator can be remarkably reduced by modifying the ZrOx surface with a thin layer of crosslinked poly(4-vinylphenol) (c-PVP). Pentacene TFTs with bare ZrOx and c-PVP stacked ZrOx gate insulators were fabricated, and their hysteresis behaviors compared. The different gate insulators exhibited no significant surface morphology or capacitance differences. The threshold voltage shift magnitude decreased by approximately 71% for the TFT with the c-PVP stacked ZrOx gate insulator compared with the bare ZrOx gate insulator, with 0.75 ± 0.05 and 0.22 ± 0.03 V threshold voltage shifts for the bare ZrOx and c-PVP stacked ZrOx gate insulators, respectively. The hysteresis reduction was attributed to effectively covering hysteresis-inducing charge trapping sites on ZrOx surfaces. Full article
(This article belongs to the Special Issue Advances in Thin Film Materials and Devices)
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13 pages, 4496 KiB  
Article
Ambipolar Transport in Methylammonium Lead Iodide Thin Film Transistors
by Jeoungmin Ji, Farjana Haque, Nhu Thi To Hoang and Mallory Mativenga
Crystals 2019, 9(10), 539; https://doi.org/10.3390/cryst9100539 - 19 Oct 2019
Cited by 13 | Viewed by 5282
Abstract
We report clear room temperature ambipolar transport in ambient-air processed methylammonium lead iodide (MAPbI3) thin-film transistors (TFTs) with aluminum oxide gate-insulators and indium-zinc-oxide source/drain electrodes. The high ionicity of the MAPbI3 leads to p-type and n-type self-doping, and depending on [...] Read more.
We report clear room temperature ambipolar transport in ambient-air processed methylammonium lead iodide (MAPbI3) thin-film transistors (TFTs) with aluminum oxide gate-insulators and indium-zinc-oxide source/drain electrodes. The high ionicity of the MAPbI3 leads to p-type and n-type self-doping, and depending on the applied bias we show that simultaneous or selective transport of electrons and/or holes is possible in a single MAPbI3 TFT. The electron transport (n-type), however, is slightly more pronounced than the hole transport (p-type), and the respective channel resistances range from 5–11 and 44–55 MΩ/μm. Both p-type and n-type TFTs show good on-state characteristics for low driving voltages. It is also shown here that the on-state current of the n-type and p-type TFTs is highest in the slightly PbI2-rich and MAI-rich films, respectively, suggesting controllable n-type or p-type transport by varying precursor ratio. Full article
(This article belongs to the Special Issue Advances in Thin Film Materials and Devices)
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8 pages, 2202 KiB  
Article
Importance of Blade-Coating Temperature for Diketopyrrolopyrrole-based Thin-Film Transistors
by Jun-Ik Park, Hyeon-Seok Jeong, Do-Kyung Kim, Jaewon Jang, In Man Kang, Philippe Lang, Yun-Hi Kim, Hyeok Kim and Jin-Hyuk Bae
Crystals 2019, 9(7), 346; https://doi.org/10.3390/cryst9070346 - 5 Jul 2019
Cited by 6 | Viewed by 5178
Abstract
In this work, the effect of blade-coating temperature on the electrical properties of a conjugated donor–acceptor copolymer containing diketopyrrolopyrrole (DPP)-based thin-film transistors (TFTs) was systematically analyzed. The organic semiconductor (OSC) layers were blade-coated at various blade-coating temperatures from room temperature (RT) to 80 [...] Read more.
In this work, the effect of blade-coating temperature on the electrical properties of a conjugated donor–acceptor copolymer containing diketopyrrolopyrrole (DPP)-based thin-film transistors (TFTs) was systematically analyzed. The organic semiconductor (OSC) layers were blade-coated at various blade-coating temperatures from room temperature (RT) to 80 °C. No remarkable changes were observed in the thickness, surface morphology, and roughness of the OSC films as the blade-coating temperature increased. DPP-based TFTs exhibited two noticeable tendencies in the magnitude of field-effect mobility with increasing blade-coating temperatures. As the temperature increased up to 40 °C, the field-effect mobility increased to 148% compared to the RT values. On the contrary, when the temperature was raised to 80 °C, the field-effect mobility significantly reduced to 20.9% of the mobility at 40 °C. These phenomena can be explained by changes in the crystallinity of DPP-based films. Therefore, the appropriate setting of the blade-coating temperature is essential in obtaining superior electrical characteristics for TFTs. A blade-coating temperature of 40 °C was found to be the optimum condition in terms of electrical performance for DPP-based TFTs. Full article
(This article belongs to the Special Issue Advances in Thin Film Materials and Devices)
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7 pages, 1528 KiB  
Commentary
A Fundamental Reason for the Need of Two Different Semiconductor Technologies for Complementary Thin-Film Transistor Operations
by Jiung Jang and Sungsik Lee
Crystals 2019, 9(11), 603; https://doi.org/10.3390/cryst9110603 - 17 Nov 2019
Cited by 6 | Viewed by 5580
Abstract
In this short commentary, we discuss a fundamental reason why two different semiconductor technologies are needed for complementary thin-film transistor (TFT) operations. It is mainly related to an energy-level matching between the band edge of the semiconductor and the work-function energy of the [...] Read more.
In this short commentary, we discuss a fundamental reason why two different semiconductor technologies are needed for complementary thin-film transistor (TFT) operations. It is mainly related to an energy-level matching between the band edge of the semiconductor and the work-function energy of the metal, which is used for the source and drain electrodes. The reference energy level is determined by the energy range of work-functions of typical metals for the source and drain electrodes. With the exception of silicon, both the conduction band edge (EC) and valence band edge (EV) of a single organic or inorganic material are unlikely to match the metal work-function energy whose range is typically from −4 to −6 eV. For example, typical inorganic materials, e.g., Zn–O, have the EC of around −4.5 eV (i.e., electron affinity), so the conduction band edge is within the range of the metal work-function energy, suggesting its suitability for n-channel TFTs. On the other hand, p-type inorganic materials, such as Cu–O, have an EV of around −5.5 eV, so the valence band edge is aligned with metal work-function energy, thus the usage for p-channel TFTs. In the case of p-type and n-type organic materials, their highest occupied molecular orbital (HOMO) and lowest occupied molecular orbital (LUMO) should be aligned with metal work-function energy. For example, p-type organic material, e.g., pentacene, has a HOMO level around −5 eV, which is within the range of the metal work-function energy, implying usage for p-channel TFTs. However, its LUMO level is around −3 eV, not being aligned with the metals’ work-function energy. So it is hard to use pentacene for n-channel TFTs. Along with this, n-type organic materials (e.g., C60) should have HOMO levels within the typical metals’ work-function energy for the usage of n-channel TFT. To support this, we provide a qualitative and comparative study on electronic material properties, such as the electron affinity and band-gap of representative organic and inorganic materials, and the work-function energy of typical metals. Full article
(This article belongs to the Special Issue Advances in Thin Film Materials and Devices)
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