Demonstration of the monolithic interconnection on CIS solar cells by picosecond laser structuring on 30 by 30 cm2 modules

In this paper, we present the selective structuring of all three patterns (P1, P2 and P3) of a monolithic interconnection of CIS (Cu(In,Ga)(S,Se)₂) thin film solar cells by picosecond laser pulses at a wavelength of 1064 nm. We show results for single pulse ablation threshold values and line scribing of molybdenum films on glass (P1), CIS on molybdenum (P2) and zinc oxide on CIS (P3). The purposes of these processes are the p‐type isolation (P1), cell interconnect (P2) and n‐type isolation (P3), which are required for complete cell architecture. The half micron thick molybdenum back electrode can be structured with a process speed of more than 15 m/s at about 15 W average power without detectable residues and damage by direct induced laser ablation from the back side (P1). The CIS layer can be structured selectively down to the molybdenum at process speeds up to 1 m/s at about 15 W average power, due to the precision of direct laser ablation in the ultrashort pulse regime (P2). The ZnO front electrode layer is separated by clean trenches with straight side walls at process speeds of up to 15 m/s at about 10 W average power, as a result of indirect induced laser ablation (P3). A validation of functionality of all processes is demonstrated on CIS solar cell modules (30 × 30 cm²). By replacing one state‐of‐the‐art process by a picosecond laser process at a time, solar efficiencies could be increased for P1 and P2 and stayed on a similar level for P3. After an optimization of the patterning processes in the R&D pilot line of AVANCIS, we achieved a new record efficiency for an all‐laser‐patterned CIS solar module: 14.7% as best value for the aperture area efficiency of a 30 × 30 cm² sized CIS module was reached. Copyright © 2014 John Wiley & Sons, Ltd.     

Phase‐Separation‐Induced Micropatterned Polymer Surfaces and Their Applications

We report a route to fabricate micropatterned polymer films with micro‐ or nanometer‐scale surface concavities by spreading polymer solutions on a non‐solvent surface. The route is simple, versatile, highly efficient, low‐cost, and easily accessible. The concavity density of the patterned films is tuned from 10⁶ to 10⁹ features cm^–2, and the concavity size is controlled in the range from several micrometers to less than 100 nm, by changing the film‐forming parameters including the polymer concentration, the temperature of the non‐solvent and the interactions between polymer, solvent, and non‐solvent. We further demonstrate that these concavity‐patterned films have significantly enhanced hydrophobicity, owing to the existence of the surface concavities, and their hydrophobicity could be controlled by the concavity density. These films have been used as templates to successfully fabricate convex‐patterned polymer films, inorganic TiO₂ microparticles, and NaCl nanocrystals. Their other potential applications are also discussed.     

Calcination‐ and Etching‐Free Photolithography of Inorganic Phosphor Films Consisting of Rare Earth Ion Doped Nanoparticles on Plastic Sheets

It is demonstrated that patterned inorganic phosphor films consisting of rare earth ion doped nanoparticles (RE‐NPs) can be fabricated on plastic sheets using calcination‐ and etching‐free photolithography. Green up‐conversion luminescence and near‐infrared (NIR) fluorescence appears from the RE‐NPs that are prepared from Y₂O₃ doped with 1 mol% Er³⁺ and 0.85 mol% Yb³⁺. The diameter of the RE‐NPs is estimated to be about 300 nm using dynamic light scattering. Visible transmittance of the RE‐NP film fabricated by dip‐coating is more than 90%. Patterned RE‐NP films are obtained by dip‐coating the RE‐NPs on patterned photoresist films fabricated by UV exposure through a photomask, followed by selective removal of the photoresist. Optical, fluorescence, scanning electron, atomic force, and Kelvin probe force microscopies are used for the characterization of the patterned RE‐NP films. The present methodology enables fabrication of patterned RE‐NP films, not only on inorganic substrates but also on plastic sheets, with low cost and material consumption.     

Patterned Transparent Conductive Au Films through Direct Reduction of Gold Thiocyanate

Construction of structurally defined, patterned metal films is a fundamental objective in the emerging and active field of bottom‐up nanotechnology. A new strategy for constructing macroscopically organized Au nanostructured films is presented. The approach is based upon a novel phenomenon in which incubation of water‐soluble Au(SCN)₄^1? complex with amine‐displaying surfaces gives rise to spontaneous crystallization and concurrent reduction, resulting in the formation of patterned metallic gold films. The Au films exhibit unique nanoribbon morphology, likely corresponding to aurophilic interactions between the complex moieties anchored to the amine groups through electrostatic attraction. Critically, no external reducing agents are needed to initiate or promote formation of the metallic Au films. In essence, the thiocyanate ligands provide the means for surface targeting of the complex, guide the Au crystallization process and, importantly, donate the reducing electrons. It is shown that the Au films exhibit electrical conductivity and high transparency over a wide spectral range, lending the new approach to possible applications in optoelectronics, catalysis, and sensing. In a broader context, a new gold chemistry route is presented in which ligand‐enabled crystallization/reduction could open the way to a wealth of innovative reaction pathways and applications.     

Heteroepitaxial Patterned Growth of Vertically Aligned and Periodically Distributed ZnO Nanowires on GaN Using Laser Interference Ablation

A simple two‐step method of fabricating vertically aligned and periodically distributed ZnO nanowires on gallium nitride (GaN) substrates is described. The method combines laser interference ablation (LIA) and low temperature hydrothermal decomposition. The ZnO nanowires grow heteroepitaxially on unablated regions of GaN over areas spanning 1 cm², with a high degree of control over size, orientation, uniformity, and periodicity. High resolution transmission electron microscopy and scanning electron microscopy are utilized to study the structural characteristics of the LIA‐patterned GaN substrate in detail. These studies reveal the possible mechanism for the preferential, site‐selective growth of the ZnO nanowires. The method demonstrates high application potential for wafer‐scale integration into sensor arrays, piezoelectric devices, and optoelectronic devices.     

Sub‐3 V ZnO Electrolyte‐Gated Transistors and Circuits with Screen‐Printed and Photo‐Crosslinked Ion Gel Gate Dielectrics: New Routes to Improved Performance

A facile, high‐resolution patterning process is introduced for fabrication of electrolyte‐gated transistors (EGTs) and circuits using a photo‐crosslinkable ion gel and stencil‐based screen printing. The photo‐crosslinkable gel is based on a triblock copolymer incorporating UV‐sensitive terminal azide functionality and a common ionic liquid. Using this material in conjunction with conventional photolithography and stenciling techniques, well‐defined 0.5–1 μm thick ion gel films are patterned on semiconductor channels as narrow as 10 μm. The resulting n‐type ZnO EGTs display high electron mobility (>2 cm² Vs^?1) and on/off current ratios (>10⁵). Further, EGT‐based inverters exhibit static gains >23 at supply voltages below 3 V, and five‐stage EGT ring oscillator circuits display dynamic propagation delays of 50 μs per stage. In general, the screen printing and photo‐crosslinking strategy provides a clean room‐compatible method to fabricate EGT circuits with improved sensitivity (gain) and computational power (gain × oscillating frequency). Detailed device analysis indicates that significantly shorter delay times, of order 1 μs, can be obtained by improving the ion gel conductance.     

4D Biofabrication: 3D Cell Patterning Using Shape‐Changing Films

A novel approach for fabrication of 3D cellular structures using new thermosensitive shape‐changing polymer films with photolithographically patterned surface—4D biofabrication is reported. The surface of shape‐changing polymer films is patterned to selectively adsorb cells in specific regions. The 2D cell pattern is converted to the 3D cell structure after temperature‐induced folding of the polymer films. This approach has a great potential in the field of tissue engineering and bioscaffolds fabrication.     

Hierarchically Ordered Arrays of Noncircular Silicon Nanowires Featured by Holographic Lithography Toward a High‐Fidelity Sensing Platform

A novel, highly uniform and tunable hybrid plasmonic array is created via ion‐milling, catalytic wet‐etching and electron‐beam evaporation, using a holographically featured structure as a milling mask. A simple and low‐cost prism holographic lithography (HL) technique is applied to create an unprecedentedly coordinated array of elliptic gold (Au) holes, which act as the silicon (Si) etching catalyst in the reaction solution used to fabricate an elliptic silicon nanowire (SiNW) array; here, the SiNWs are arrayed hierarchically in such a way that three SiNWs are triangularly coordinated, and the triangles are arranged hexagonally. After removing the polymeric mask and metal thin film, the highly anisotropic thick Au film is deposited on the SiNW arrays. This hybrid substrate shows tunable optical properties in the near‐infrared (NIR) region from 875 nm to 1030 nm and surface‐enhanced Raman scattering (SERS) activities; these characteristics depend on the catalytic wet etching time, which changes the size of the vertical gap between the Au thick films deposited separately on the SiNWs. In addition, lateral interparticle coupling induces highly intensified SERS signals with good homogeneity. Finally, the Au‐capped elliptical SiNW arrays can be hierarchically patterned by combining prism HL and conventional photolithography, and the highly enhanced fluorescence intensity associated with both the structural effects and the plasmon resonances is investigated.     

Flash‐Assisted Processing of Highly Conductive Zinc Oxide Electrodes from Water

Fabricating high‐quality transparent conductors using inexpensive and industrially viable techniques is a major challenge toward developing low cost optoelectronic devices such as solar cells, light emitting diodes, and touch panel displays. In this work, highly transparent and conductive ZnO thin films are prepared from a low‐temperature, aqueous deposition method through the careful control of the reaction chemistry. A robotic synthetic platform is used to explore the wide parameter space of a chemical bath system that uses only cheap and earth abundant chemicals for thin film deposition. As‐deposited films are found to be highly resistive, however, through exposure to several millisecond pulses of high‐intensity, broadband light, intrinsically doped ZnO films with sheet resistances as low as 40 Ω □^?1 can be readily prepared. Such values are comparable with state‐of‐the‐art‐doped transparent conducting oxides. The mild processing conditions (<150 °C) of the ZnO electrodes also enable their deposition on temperature sensitive substrates such as PET, paving the way for their use in various flexible optoelectronic devices. Proof‐of‐concept light emitting devices employing ZnO as a transparent electrode are presented.     

Structural and Electrical Characterization of ZnO Films Grown by Spray Pyrolysis and Their Application in Thin‐Film Transistors

The role of the substrate temperature on the structural, optical, and electronic properties of ZnO thin films deposited by spray pyrolysis using a zinc acetate precursor solution is reported. Analysis of the precursor compound using thermogravimentry and differential scanning calorimetry indicates complete decomposition of the precursor at around 350 °C. Film characterization using Fourier Transform Infrared Spectroscopy (FTIR), photoluminescence spectroscopy (PL), and ultraviolet–visible (UV–Vis) optical transmission spectroscopy suggests the onset of ZnO growth at temperatures as low as 100 °C as well as the transformation to a polycrystalline phase at deposition temperatures >200 °C. Atomic force microscopy (AFM) and X‐ray diffraction (XRD) reveal that as‐deposited films exhibit low surface roughness (rms ≈ 2.9 nm at 500 °C) and a crystal size that is monotonously increasing from 8 to 32 nm for deposition temperatures in the range of 200–500 °C. The latter appears to have a direct impact on the field‐effect electron mobility, which is found to increase with increasing ZnO crystal size. The maximum mobility and current on/off ratio is obtained from thin‐film transistors fabricated using ZnO films deposited at >400 °C yielding values on the order of 25 cm² V^?1s^?1 and 10⁶, respectively.     

All‐Solution‐Processed Indium‐Free Transparent Composite Electrodes based on Ag Nanowire and Metal Oxide for Thin‐Film Solar Cells

Fully solution‐processed Al‐doped ZnO/silver nanowire (AgNW)/Al‐doped ZnO/ZnO multi‐stacked composite electrodes are introduced as a transparent, conductive window layer for thin‐film solar cells. Unlike conventional sol–gel synthetic pathways, a newly developed combustion reaction‐based sol–gel chemical approach allows dense and uniform composite electrodes at temperatures as low as 200 °C. The resulting composite layer exhibits high transmittance (93.4% at 550 nm) and low sheet resistance (11.3 Ω sq^‐1), which are far superior to those of other solution‐processed transparent electrodes and are comparable to their sputtered counterparts. Conductive atomic force microscopy reveals that the multi‐stacked metal‐oxide layers embedded with the AgNWs enhance the photocarrier collection efficiency by broadening the lateral conduction range. This as‐developed composite electrode is successfully applied in Cu(In_1‐x,Ga_x)S₂ (CIGS) thin‐film solar cells and exhibits a power conversion efficiency of 11.03%. The fully solution‐processed indium‐free composite films demonstrate not only good performance as transparent electrodes but also the potential for applications in various optoelectronic and photovoltaic devices as a cost‐effective and sustainable alternative electrode.     

图形化氧化锌阵列的制备及其场发射性能研究

为了减小场发射的屏蔽效应,采用图形化技术对氧化锌(ZnO)纳米枝阵列进行调控,并研究图形化ZnO枝阵列的性能。首先采用光刻法在ITO导电玻璃上制备图形化ZnO种子层,再用电沉积法在图形化种子层上生长ZnO纳米枝阵列。利用扫描电子显微镜(SEM)、X射线衍射(XRD)研究所制备的图形化ZnO阵列形貌、结构等,并测试其场发射性能。研究结果表明,制备的图形化ZnO纳米枝是圆阵列,直径为330μm左右,纳米ZnO主干平均直径为400~500nm,发现主干上有一些精细的类似锥状的纳米量级微细枝结构,并且具有良好的场发射性能,开启场强为2.15V/μm,场增强因子为16 109。该图形化生长ZnO阵列阴极的方法是一种能较好改善材料场发射性能的方法,在场发射应用领域表现出较好的前景。     

Growth of Heteroepitaxial ZnO Thin Films on GaN‐Buffered Al2O3 (0001) Substrates by Low‐Temperature Hydrothermal Synthesis at 90 °C

Heteroepitaxial ZnO films are successfully grown on nondoped GaN‐buffered Al₂O₃ (0001) substrates in water at 90 °C using a two‐step process. In the first step, a discontinuous ZnO thin film (ca. 200 nm in thickness) consisting of hexagonal ZnO crystallites is grown in a solution containing Zn(NO₃)·6 H₂O and NH₄NO₃ at ca. pH 7.5 for 24 h. In the second step, a dense and continuous ZnO film (ca. 2.5 μm) is grown on the first ZnO thin film in a solution containing Zn(NO₃)·6 H₂O and sodium citrate at ca. pH 10.9 for 8 h. Scanning electron microscopy, X‐ray diffraction, UV‐vis absorption spectroscopy, photoluminescence spectroscopy, and Hall‐effect measurement are used to investigate the structural, optical, and electrical properties of the ZnO films. X‐ray diffraction analysis shows that ZnO is a monocrystalline wurtzite structure with an epitaxial orientation relationship of (0001)[11 0]_ZnO∥(0001)[11 0]_GaN. Optical transmission spectroscopy of the two‐step grown ZnO film shows a bandgap energy of 3.26 eV at room temperature. A room‐temperature photoluminescence spectrum of the ZnO film reveals only a main peak at ca. 380 nm without any significant defect‐related deep‐level emissions. The electrical property of ZnO film showed n‐type behavior with a carrier concentration of 3.5 × 10¹⁸ cm^–3 and a mobility of 10.3 cm² V^–1 s^–1.     

Structural Electrochemistry: Conductivities and Ionic Content from Rising Reduced Polypyrrole Films

Free‐standing polypyrrole films are submitted in NaCl aqueous solutions with different potentials corresponding to the swollen, closed, or reduced and rising conformational packed states, defined from the closed coulovoltammetric responses in the potential range between –1.5 and 0.65 V versus Ag/AgCl. Decreasing anion content from rising reduced and conformational packed films is detected by energy‐dispersive X‐ray spectroscopy (EDX) analysis. The cation, Na⁺, is not present in the studied samples. At the closing potential, the film keeps over 30% of the counterions present in a fully oxidized film. The film reduction‐compaction process at high cathodic potentials consumes over 15% of the full redox charge, expelling a similar percentage of counterions. By using free‐standing PPy‐DBS films, the Na⁺ content increases for rising reduced states, but some increase of the chloride content is attained for deep oxidized and packed states. This polypyrrole blend experiences a major exchange of cations for charge balance. Some polypyrrole chains not balanced by DBS require perchlorate exchange at high anodic potentials. The continuous decrease of anion content promotes in polypyrrole films a parallel decrease of the electronic conductivities obtained in nitrogen atmosphere. Ionic content and conductivities in polypyrrole films support that the two structural reduction (shrinking and compaction) processes correspond to the same reaction: the injection of electrons and expulsion of counterions with two different kinetics imposed by two reaction‐induced 3D structures (swollen or closed and rising packed) in the film.     

Highly Customizable All Solution–Processed Polymer Light Emitting Diodes with Inkjet Printed Ag and Transfer Printed Conductive Polymer Electrodes

Inkjet and transfer printing processes are combined to easily form patterned poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) films as top anodes of all solution–processed inverted polymer light emitting diodes (PLEDs) on rigid glass and flexible plastic substrates. An adhesive PEDOT:PSS ink is formulated and fully customizable patterns are obtained using the inkjet printing process. In order to transfer the patterned PEDOT:PSS films, adhesion properties at interfaces during multistep transfer printing processes are carefully adjusted. The transferred PEDOT:PSS film on the plastic substrates shows not only a sheet resistance of 260.6 Ω/□ and a transmittance of 92.1% at 550 nm wavelength but also excellent mechanical flexibility. The PLEDs with spin‐coated functional layers sandwiched between the transferred PEDOT:PSS top anodes and inkjet‐printed Ag bottom cathodes are fabricated. The fabricated PLEDs on the plastic substrates show a high current efficiency of 10.4 cd A^?1 and high mechanical stability. It is noted that because both Ag and PEDOT:PSS electrodes can be patterned with a high degree of freedom via the inkjet printing process, highly customizable PLEDs with various pattern sizes and shapes are demonstrated on the glass and plastic substrates. Finally, with all solution process, a 5 × 7 passive matrix PLED array is demonstrated.     

High rate (~7 nm/s), atmospheric pressure deposition of ZnO front electrode for Cu(In,Ga)Se2 thin‐film solar cells with efficiency beyond 15%

Undoped zinc oxide (ZnO) films have been grown on a moving glass substrate by plasma‐enhanced chemical vapor deposition at atmospheric pressure. High deposition rates of ~7 nm/s are achieved at low temperature (200 °C) for a substrate speed from 20 to 60 mm/min. ZnO films are highly transparent in the visible range (90%). By a short (~minute) post‐deposition exposure to near‐ultraviolet light, a very low resistivity value of 1.6·10⁻³ Ω cm for undoped ZnO is achieved, which is independent on the film thickness in the range from 180 to 1200 nm. The photo‐enhanced conductivity is stable in time at room temperature when ZnO is coated by an Al₂O₃ barrier film, deposited by the industrially scalable spatial atomic layer deposition technique. ZnO and Al₂O₃ films have been used as front electrode and barrier, respectively, in Cu(In,Ga)Se2 (CIGS) solar cells. An average efficiency of 15.4 ± 0.2% (15 cells) is obtained that is similar to the efficiency of CIGS reference cells in which sputtered ZnO:Al is used as electrode. Copyright © 2013 John Wiley & Sons, Ltd.     

Patterning Liquid Crystalline Organic Semiconductors via Inkjet Printing for High-Performance Transistor Arrays and Circuits

Liquid crystalline (LC) organic semiconductors having long-range-ordered LC phases hold great application potential in organic field-effect transistors (OFETs). However, to meet real device application requirements, it is a prerequisite to precisely pattern the LC film at desired positions. Here, a facile method that combines the technique of inkjet printing and melt processing to fabricate patterned LC film for achieving high-performance organic integrated circuits is demonstrated. Inkjet printing controls the deposition locations of the LC materials, while the melt processing implements phase transition of the LC materials to form high-quality LC films with large grain sizes. This approach enables to achieve patterned growth of high-quality 2,7-dioctyl[1]-benzothieno[3,2-b][1]benzothiophene (C₈-BTBT) LC films. The patterned C₈-BTBT LC film-based 7 × 7 OFET array has 100% die yield and shows high average mobility of 6.31 cm² V⁻¹ s⁻¹, along with maximum mobility up to 9.33 cm² V⁻¹ s⁻¹. As a result, the inverters based on the patterned LC films reach a high gain up to 23.75 as well as an ultrahigh noise margin over 81.3%. Given the good generality of the patterning process and the high quality of the resulting films, the proposed method paves the way for high-performance organic integrated devices.     

ZnO纳米棒的图形化生长及其场发射特性

介绍了用氢离子注入技术和阳极腐蚀方法在硼掺杂p-(100)型硅晶片上制备图形化的纳米硅(SiNC)薄膜工艺，并在这种图形化衬底上成功生长了图形化的ZnO纳米棒. 场发射测试表明制备的ZnO纳米棒具有良好的场发射性能，即具有较低的开启电场和阈值电场，较高的发射点密度.     

Enhanced Quality of Wafer‐Scale MoS2 Films by a Capping Layer Annealing Process

Wafer‐scale, single‐crystalline 2D semiconductors without grain boundaries and defects are needed for developing reliable next‐generation integrated 2D electronics. Unfortunately, few literature reports exist on the growth of 2D semiconductors with single‐crystalline structure at the wafer scale. It is shown that direct sulfurization of as‐deposited epitaxial MoO₂ films (especially, with thicknesses more than ≈5 nm) produces textured MoS₂ films. This texture is inherited from the high density of defects present in the as‐prepared epitaxial MoO₂ film. In order to eliminate the texture of the converted MoS₂ films, a new capping layer annealing process (CLAP) is introduced to improve the crystalline quality of as‐deposited MoO₂ films and minimize its defects. It is demonstrated that sulfurization of the CLAP‐treated MoO₂ films leads to the formation of single‐crystalline MoS₂ films, instead of textured films. It is shown that the single‐crystalline MoS₂ films exhibit field‐effect mobility of 6.3 cm² V^?1 s^?1, which is 15 times higher than that of textured MoS₂. These results can be attributed to the smaller concentration of defects in the single‐crystalline films.     

Room-temperature ferromagnetic ordering in Mn-doped ZnO thin films grown by pulsed laser deposition

The ferromagnetic ordering in Mn-doped ZnO thin films grown by pulsed laser deposition (PLD) as a function of oxygen pressure and substrate temperature has been investigated. Room-temperature ferromagnetic behaviors in the Mn-doped ZnO films grown at 700°C and 800°C under 10⁻¹ torr in oxygen pressure were found, whereas ferromagnetic ordering in the films grown under 10⁻³ torr disappeared at 300 K. The large positive magnetoresistance (MR), ∼10%, was observed at 5 K at low fields and small negative MR was observed at high fields, irrespective of oxygen pressure. In particular, anomalous Hall effect (AHE) in the Mn-doped ZnO film grown at 700°C under 10⁻¹ Torr has been observed up to 210 K. In this work, the observed AHE is believed to be further direct evidence demonstrating that the Mn-doped ZnO thin films are ferromagnetic.