We report systematic design and formation of plasmonic perovskite solar cells (PSCs) by integrating Au@TiO2 core–shell nanoparticles (NPs) into porous TiO2 and/or perovskite semiconductor capping layers. The plasmonic effects in the formed PSCs are examined. The most efficient configuration is obtained by incorporating Au@TiO2 NPs into both the porous TiO2 and the perovskite capping layers, which increases the power conversion efficiency (PCE) from 12.59% to 18.24%, demonstrating over 44% enhancement, compared with the reference device without the metal NPs. The PCE enhancement is mainly attributed to short-circuit current improvement. The plasmonic enhancement effects of Au@TiO2 core–shell nanosphere photovoltaic composites are explored based on the combination of UV–vis absorption spectroscopy, external quantum efficiency (EQE), photocurrent properties, and photoluminescence (PL). The addition of Au@TiO2 nanospheres increased the rate of exciton generation and the probability of exciton dissociation, enhancing charge separation/transfer, reducing the recombination rate, and facilitating carrier transport in the device. This study contributes to understanding of plasmonic effects in perovskite solar cells and also provides a promising approach for simultaneous photon energy and electron management.Keywords: Au nanoparticles; exciton dissociation; exciton generation; near-field; perovskite solar cells; plasmon enhancement;

In this work, enhanced photovoltaic performance and light stability of perovskite solar cells (PSCs) was achieved by applying down conversion (DC) CeO2:Eu3+ nanophosphor—TiO2 composite electrodes and the related mechanism are reported. High-yield CeO2:Eu3+ nanocrystals were synthesized by a simple hydrothermal method with combinational use of trisodium phosphate dodecahydrate and sodium hydroxide. Uniform and efficient CeO2:Eu3+ nanophosphors were prepared at an optimized reaction time. The optimal CeO2:Eu3+ nanophosphors were 70 nm in size, with octahedral and mirrorlike facets that provided excellent DC luminescence. The CeO2:Eu3+ nanophosphors grown at the optimal conditions were incorporated into mesoporous TiO2 layers of PSC devices. The PSC device with the CeO2:Eu3+—TiO2 composite electrode exhibited an energy conversion efficiency of 10.8%, which improved efficiency by 35% relative to the referenced one with undoped CeO2 nanocrystals. PSC devices added with undoped and doped CeO2 nanocrystals exhibited significantly better stability toward UV light compared to the bare TiO2 based PSC cell. The fundamental optics behind light propagation and absorption in perovskite solar cell and concept of using DC nanophosphors to improve the device performance has been explored. In this study, an attempt was made to elucidate the multi-roles of DC nanoconverters in mesoporous TiO2 based PSCs.

The morphology of electron transport layers has a significant impact on the device architecture and electronic processes of mesoscopic perovskite solar cells (PSCs). In this study, ultrathin MgO is coated on the surface of compact TiO2 (c-TiO2). The MgO-coated c-TiO2 is first used as seeds to hydrothermally grow one-dimensional (1D) TiO2 nanorod (NR) arrays for PSC devices. Rutile nanorod arrays are fabricated via a facile solvothermal method using tetrabutyl titanate (TBT) as the Ti precursor. The microstructures and morphologies, including nanorod diameter, length, and areal density, of the TiO2 NR arrays are varied by controlling the concentration of TBT from 0.3 M to 0.7 M. Furthermore, the profound effects of the MgO modification and titania nanorod morphology on the pore-filling of perovskite CH3NH3PbI3, charge separation and recombination at the perovskite/titania nanorod interface are investigated. Our results reveal that the Ti precursor concentration strongly affects the open-circuit voltage (VOC), short-circuit current density (JSC), and fill factor (FF) of the 1D TiO2 NR array-based device. Under optimized conditions with MgO coating and at 0.4 M TBT, our champion cell with 1D TiO2 NRs demonstrates a power conversion efficiency (PCE) of 17.03% with JSC = 22.01 mA cm−2, VOC = 1.06 V, and FF = 0.73. Under the same fabrication conditions, MgO modification enhances the average PCE to 16.24% for the PSCs with the MgO coating from 13.38% for the PSCs without the MgO coating. The devices show an approximately 18% improvement in performance, which mainly results from the open-circuit voltage and fill factor enhancements. Moreover, advantageously, the MgO modification is found to reduce the current density–voltage (J–V) hysteresis with respect to the scan direction and improve the UV stability of the non-encapsulated cells. Therefore, this study presents a promising approach to fabricate efficient and stable one-dimensional TiO2 nanorod array-based perovskite solar cells.

Achieving high open-circuit voltage and high short-circuit current density simultaneously is a big challenge in the development of highly efficient perovskite solar cells, due to the complex excitonic nature of hybrid organic–inorganic semiconductors. Herein, we developed a facile and effective method to fabricate efficient plasmonic PSC devices. The solar cells were prepared by incorporating Au nanoparticles (NPs) into mesoporous TiO2 films and depositing a MgO passivation film on the Au NP-modified mesoporous titania via wet spinning and pyrolysis of magnesium salt. The PSCs obtained by combining Au NPs and MgO demonstrated a high power conversion efficiency of 16.1%, with both a high open-circuit voltage of 1.09 V and a high short-circuit current density of 21.76 mA cm−2. The device achieved a 34.2% improvement in the power conversion efficiency compared with a device based on pure TiO2. Moreover, a significant improvement of the UV stability in the perovskite solar cell was achieved due to the combined use of Au NPs and insulating MgO. The fundamental optics and physics behind the regulation of energy flow in the perovskite solar cell and the concept of using Au NPs and MgO to improve the device performance were explored. The results indicate that the combined use of Au NPs and a MgO passivation film is an effective way to design high performance and high stability organic–inorganic perovskite photovoltaic materials.

A solvent-assisted methodology has been developed to synthesize CH3NH3PbI3 perovskite absorber layers. It involved the use of a mixed solvent of CH3NH3I, PbI2, γ-butyrolactone, and dimethyl sulfoxide (DMSO) followed by the addition of chlorobenzene (CB). The method produced ultra-flat and dense perovskite capping layers atop mesoporous TiO2 films, enabling a remarkable improvement in the performance of free hole transport material (HTM) carbon electrode-based perovskite solar cells (PSCs). Toluene (TO) was also studied as an additional solvent for comparison. At the annealing temperature of 100 °C, the fabricated HTM-free PSCs based on drop-casting CB demonstrated power conversion efficiency (PCE) of 9.73 %, which is 36 and 71 % higher than those fabricated from the perovskite films using TO or without adding an extra solvent, respectively. The interaction between the PbI2–DMSO–CH3NH3I intermediate phase and the additional solvent was discussed. Furthermore, the influence of the annealing temperature on the absorber film formation, morphology, and crystalline structure was investigated and correlated with the photovoltaic performance. Highly efficient, simple, and stable HTM-free solar cells with a PCE of 11.44 % were prepared utilizing the optimum perovskite absorbers annealed at 120 °C.

We report efficient mixed halide perovskite solar cells using thermally evaporated Ag or AgAl alloy layers as back electrodes. The properties of AgAl alloy and Ag films deposited on a hole-transport material layer for use in CH3NH3PbI3−xClx solar cells were investigated. The influence of the distance between the metal source and the sample on the performance of the solar cells was determined. The cell with an Ag layer deposited at a distance of 20 cm displayed a power conversion efficiency (PCE) of 5.49%. When the Ag layer was deposited at a distance of 30 cm, the resulting device achieved a 46.8% enhancement in PCE compared to the cell with the Ag prepared at 20 cm. Furthermore, the AgAl alloy based perovskite solar cell accomplished a 37.3% enhancement in PCE compared to the optimized Ag electrode. The fabricated AgAl alloy perovskite cells show a fill factor of 59.6%, open-circuit voltage of 0.88 V, short-circuit current density of 21.11 mA cm−2, yielding an overall efficiency of 11.07%. The AgAl alloy layer exhibited high optical reflectivity and good adhesion on the hole-transport material layer compared to a layer of Ag. The PCE enhancement mechanisms are discussed. Our work has demonstrated that AgAl is a promising back electrode material for high-efficiency perovskite solar cells.

One dimensional (1D) NiS/2D graphene nanocomposites were synthesized via a simple, facile, and low-temperature hydrothermal method and used as cocatalysts for triiodide reduction in dye sensitized solar cell (DSSCs). The influence of the graphene content on the microstructure and morphology of the NiS/graphene hybrid was investigated. Catalytic activities of the composite catalysts for reduction of I3− were characterized by electrochemical impedance spectroscopy and cyclic voltammetry. It was found that the content of graphene played an important role in the structure and the quality of the formed NiS/graphene hybrid counter-electrode (CE) and the photovoltaic performance of the resultant DSSC as well. The mechanisms for the NiS/graphene hybrid formation and electrocatalytic performance improvement are discussed. The NiS/graphene hybrid CE exhibits the best catalytic property when the mass ratio of graphene to NiS is 0.4 %. The DSSC with the optimized NiS/graphene hybrid CE produces an energy conversion efficiency of 8.26 %, which is significantly higher than that of the device with pure graphene or bare NiS CE, and also superior to that (8.12 %) for the DSSC with the Pt CE under the same conditions.

We report a facile and simple approach for growing low-cost and mixed-phase cobalt sulfide counter-electrodes (CEs) for efficient dye sensitized solar cells (DSSCs). The whole process involves growth of cobalt sulfide powders using a solution containing cobalt acetate and sodium sulfide by a chemical precipitation method at room temperature, preparation of cobalt sulfide pastes with ethyl cellulose, formation of cobalt sulfide films by screen-printing method, and treatment of the formed cobalt sulfide layers at 400 °C. Mixed-phase cobalt sulfide was formed on the FTO substrate after annealing. The electronic and ionic processes in platinum and cobalt sulfide based DSSCs are examined, analyzed and compared. Highly efficient DSSCs with mixed-phase cobalt sulfide CEs have been fabricated. The DSSC featuring a mixed-phase cobalt sulfide electrode achieved an energy efficiency as high as 7.2 %. The proposed cobalt sulfide CE manufacturing method is cheap and scalable. It can make large-scale electro-catalytic film fabrication cost competitive for both energy harvesting and storage applications.

We present for the first time the synthesis of Eu3+-doped β-phase sodium gadolinium fluoride (NaGdF4:Eu) nanocrystals (NCs) using a hydrothermal method and the application of down conversion (DC) NaGdF4:Eu NCs to efficient dye-sensitized solar cells (DSSCs). The as-prepared NaGdF4:Eu3+ NCs were characterized by X-ray diffraction, photoluminescence spectrometry, and scanning and transmission electron microscopy. DC layers consisting of poly(methyl methacrylate) (PMMA) doped with luminescent NaGdF4:Eu3+ were prepared and attached onto the back of a prefabricated TiO2 anode to form a more efficient DSSC, compared with a device based on a pure TiO2 electrode. The influences of both doped and undoped NaGdF4 NC layers on the photovoltaic devices were compared and evaluated by the measurement of the device’s incident-photon-to-current efficiency (IPCE). An obvious increase in IPCE was observed when the DC layer was added in the device. As the down-converted photons can be reabsorbed within DSSCs to generate photocurrent, the DSSC with a 100 nm thick NaGdF4:Eu3+ DC-PMMA layer improved photoelectric conversion efficiency by 4.5% relative to the uncoated solar cell. The experiments conclude that NaGdF4:Eu3+ nanocrystals mainly act as luminescent DC centers and light scatterers in the ultraviolet and visible domains, respectively, for enhancing the spectral response of the device in the measured spectral regime.Keywords: down-converting material; dye-sensitized solar cell; lanthanide-doped; NaGdF4; nanocrystal

Cobalt selenide (Co0.85Se) counter electrodes (CEs) were synthesized in situ on plasma-treated fluorine-doped tin oxide (FTO) substrates using a hydrothermal approach. FTO glass substrates were treated using O2/Ar direct current (DC) plasma for 5 min prior to the cobalt selenide growth. It was found that Co0.85Se developed horizontally and vertically oriented, submicron or micron sized, and tremelliform-like structures on the plasma-modified FTO surface. This unique Co0.85Se nanomaterial had a much larger accessible surface area, more active catalytic sites, and better catalytic properties compared to the case without plasma treatment. The electronic and ionic processes in dye sensitized solar cells (DSSCs) based on cobalt selenide CEs with or without plasma treatment as well as the Pt CE were analyzed and compared. The device with the Co0.85Se on the plasma-treated FTO produced an energy conversion efficiency of 8.04%, which is significantly superior to that for the DSSC with the Pt CE (7.66%) and also higher than that (7.88%) for the device with the Co0.85Se CE on the pristine FTO without plasma treatment. Plasma treatment of transparent conducting oxides has been proposed as an effective method for in situ deposition of high-quality inorganic compound CE nanomaterials and improving the electrocatalytic activities of inorganic compound CEs.

The present paper describes a new method for manufacturing large scale, stable, transportable, and designable nanostructured porous TiO2 tapes on various substrates for use in photoelectrochemical cells. The method involves predeposition of TiO2 strips on the fluorine doped tin oxide (FTO) glass by screen-printing method, peeling off TiO2 strips from the substrate by a novel laser-assisted lift-off technique, sintering the formed TiO2 tapes at 500 °C for 15 min, and compressing the sintered TiO2 tapes on different conductive substrates with a low pressure rolling press to form mechanically stable, electrically conducting, porous nanostructured TiO2 electrodes at room temperature. Photoelectrochemical characteristics of the resulted electrodes are presented. Dye-sensitized solar cells (DSSCs) with the as-fabricated TiO2 photoanodes on PET-ITO and FTO glass achieved a conversion efficiency of 4.2% and 6.2%, respectively. The potential use of this new manufacturing method in future DSSC applications is discussed.Keywords: dye-sensitized solar cell; laser-assisted lift-off; layer transfer; low temperature; rolling press; TiO2 tape;

Sn-based quaternary material, Cu2ZnSnS4 (CZTS), was successfully synthesized using an inexpensive and quick wet chemical route. The obtained CZTS nanocrystals were characterized by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM) and selected area electron diffraction (SAED) techniques. XRD and SAED results revealed that kesterite CZTS was formed. The formed CZTS nanocrystals were slightly irregularly faceted particles with diameters between 5 nm and 25 nm. CZTS was studied as an anode material in rechargeable lithium ion battery for the first time. The Cu2ZnSnS4 annealed at 500 °C showed a capacity of about 540 mA h g−1 at the initial stage. The first cycle of the CZTS electrode exhibited enormously irreversible capacity. The result indicated that the formation of metallic Sn from the Cu2ZnSnS4 powder was similar to the case in SnO2 or SnS2 electrodes. Cu2ZnSnS4 was demonstrated to be one of the possible candidates of the anode materials for future lithium ion battery.Highlights► Inexpensive and quick wet chemical route was used to synthesize the quaternary kesterite Cu2ZnSnS4. ► Nontoxic octadecylamine system was used as a solvent and a stabilizer in the synthesis process. ► Cu2ZnSnS4 has been studied as an anode material in the lithium ion batteries for the first time.

We investigated the characteristics of TiO2 compact layers grown by RF and pulsed DC magnetron sputtering on F-doped SnO2 (FTO) electrodes from a TiO2 ceramic target. The morphological and microstructural properties of the formed TiO2 layers were characterized by scanning electronic microscopy and X-ray diffraction. The deposition rate of the compact TiO2 layer by pulsed DC sputtering was much higher than that of RF deposition under the same sputter power and deposition pressure. Moreover, it was found that the power conversion efficiency of the dye-sensitized solar cells (DSCs) is strongly dependent on the thickness of both RF and DC sputtered TiO2 layer inserted between FTO electrode and nanoporous TiO2 layer. The thickness of the sputtered TiO2 layer was changed from 0 to 200 nm. The electrochemical impedance spectroscopy (EIS) technique was employed to evaluate the recombination resistance and electron lifetime in DSCs with differently thick TiO2 passivating films. The DSC fabricated on 160 nm thick TiO2 passivating FTO electrode showed the maximum power conversion efficiency of 7.90% due to highly effective prevention of the electron transfer to electrolyte.Highlights► TiO2 compact layers grown by RF and pulsed DC magnetron sputtering. ► Higher deposition rate was obtained by pulsed DC sputtering. ► The performance of DSCs is dependent on the thickness of sputtered TiO2 layer. ► DSC with 160 nm TiO2 compact layer got an efficiency of 7.90% by DC sputtering.

We explore a simple and eco-friendly approach for preparing CZTS powders and a screen-printing process for Cu2ZnSn(S,Se)4 (CZTSSe) counter electrodes (CEs) in dye-sensitized solar cells (DSCs). Cu2ZnSnS4 (CZTS) nanoparticles have been synthesized via a hydrazine-free solvothermal approach without the assistance of organic ligands. CZTS has been prepared by directly drop-casting the CZTS ink on the cleaned FTO glass, while CZTSSe CEs have been fabricated by screen-printing CZTS pastes, followed by post selenization using Se vapor obtained from elemental Se pellets. The crystal structure, composition and morphology of the as-deposited CZTS nanoparticles and CZTSSe electrodes are characterized by X-ray diffractometer, energy dispersive spectrometer, field emission scanning electron microscopy and transmission electron microscopy. The electrochemical properties of CZTS, CZTSSe and Pt CE based DSCs are examined and analyzed by electrochemical impedance spectroscopy. The prepared CZTS and CZTSSe CEs exhibit a cellular structure with high porosity. DSCs fabricated with CZTSSe CEs achieve a power conversion efficiency of 5.75% under AM 1.5 G illumination with an intensity of 100 mW/cm2, which is higher than that (3.22%) of the cell using the CZTS CE. The results demonstrate that the CZTSSe CE possesses good electrocatalytic activity for the reduction of charge carriers in electrolyte. The comprehensive CZTSSe CE process is cheap and scalable. It can make large-scale electro-catalytic film fabrication cost competitive for both energy harvesting and storage applications.

Graphene nanosheets (GNs) were synthesized and used as a substitute for platinum as counter-electrode materials for dye-sensitized solar cells (DSSCs). The as-synthesized GNs were dispersed in a mixture of terpineol and ethyl cellulose. GN films were screen-printed on fluorine-doped tin oxide (FTO) slides using the formed GN dispersions. GN counter-electrodes were produced by annealing the GN films at different temperatures. The annealed GN films revealed an unusual 3D network structure. Structural and electrochemical properties of the formed GN counter-electrodes were examined by field emission scanning electron microscopy, Raman spectroscopy and electrochemical impedance spectroscopy. It was found that the annealing temperature of GN materials played an important role in the quality of the GN counter-electrode and the photovoltaic performance of the resultant DSSC. The grown DSSCs with graphene-based counter-electrodes exhibited a conversion efficiency high up to 6.81%.

In based mixture Inx(OH,S)y buffer layers deposited by chemical bath deposition technique are a viable alternative to the traditional cadmium sulfide buffer layer in thin film solar cells. We report on the results of manipulating the absorber/buffer interface between the chalcopyrite Cu(In,Ga)Se2 (CIGS) absorber and CdS or ZnS buffer by addition of a thin In based mixture layer. It is shown that the presence of thin Inx(OH,S)y at the CIGS absorber/CdS or ZnS buffer interfaces greatly improve the solar cell performances. The performances of CIGS cells using dual buffer layers composed of Inx(OH,S)y/CdS or Inx(OH,S)y/ZnS increased by 22.4% and 51.6%, as compared to the single and standard CdS or ZnS buffered cells, respectively.

A flexible counter electrode (CE) for dye-sensitized solar cells (DSCs) has been fabricated using a micro-porous polyvinylidene fluoride membrane as support media and sputtered Pt as the catalytic material. Non-conventional structure DSCs have been developed by the fabricated CEs. The Pt metal was sputtered onto one surface of the membrane as the catalytic material. DSCs were assembled by attaching the TiO2 electrode to the membrane surface without Pt coating. The membrane was with cylindrical pore geometry. It served not only as a substrate for the CE but also as a spacer for the DSC. The fabricated DSC with the flexible membrane CE showed higher photocurrent density than the conventional sandwich devices based on chemically deposited Pt/FTO glass, achieving a photovoltaic conversion efficiency of 4.43%. The results provides useful information in investigation and development of stable, low-cost, simple-design, flexible and lightweight DSCs.

Titanium dioxide nanotubes (TiNTs) were fabricated from commercial P25 TiO2 powders via alkali hydrothermal transformation. Dye-sensitized solar cells (DSCs) were constructed by application of TiNTs and P25 nanoparticles with various weight percentages. The influence of the TiNT concentration on the performance of DSCs was investigated systematically. The electrochemical impedance spectroscopy (EIS) technique was employed to quantify the recombination resistance, electron lifetime and time constant in DSCs both under illumination and in the dark. The DSC based on TiNT/P25 hybrids showed a better photovoltaic performance than the cell purely made of TiO2 nanoparticles. The open-voltage (Voc), fill factor (FF) and efficiency (η) continuously increased with the TiO2 nanotube concentration from 0 to 50 wt%, which was correlated with the suppression of the electron recombination as found out from EIS studies. Respectable photovoltaic performance of ca. 7.41% under the light intensity of 100 mW cm−2 (AM 1.5G) was achieved for DSCs using 90 wt% TiO2 nanotubes incorporated in TiO2 electrodes.

Aluminum-doped ZnO (AZO) transparent conducting films were deposited on glass substrates with and without intrinsic ZnO (i-ZnO) buffer layers by a home made and low cost radio-frequency (RF) magnetron sputtering system at room temperature in pure argon ambient and under a low vacuum level. The films were examined and characterized for electrical, optical, and structural properties for the application of CIGS solar cells. The influence of sputter power, deposition pressure, film thickness and residual pressure on electrical and optical properties of layered films of AZO, i-ZnO and AZO/i-ZnO was investigated. The optimization of coating process parameters (RF power, sputtering pressure, thickness) was carried out. The effects of i-ZnO buffer layer on AZO films were investigated. By inserting thin i-ZnO layers with a thickness not greater than 125 nm under the AZO layers, both the carrier concentration and Hall mobility were increased. The resistivity of these layered films was lower than that of single layered AZO films. The related mechanisms and plasma physics were discussed. Copper indium gallium selenide (CIGS) thin film solar cells were fabricated by incorporating bi-layer ZnO films on CdS/CIGS/Mo/glass substrates. Efficiencies of the order of 7–8% were achieved for the manufactured CIGS solar cells (4–5 cm2 in size) without antireflective films. The results demonstrated that RF sputtered layered AZO/i-ZnO films are suitable for application in low cost CIGS solar cells as transparent conductive electrodes.

Double-walled carbon nanotubes (DWCNTs) have been studied for counter-electrode application in dye-sensitized solar cells (DSCs). Mesoporous TiO2 films are prepared from the commercial TiO2 nanopowders by screen-printing technique on optically transparent-conducting glasses. A metal-free organic dye (indoline dye D102) is used as a sensitizer. DWCNTs are applied to substitute for platinum as counter-electrode materials. Morphological and electrochemical properties of the formed counter electrodes are investigated by scanning electronic microscopy and electrochemical impedance spectroscopy, respectively. The electronic and ionic processes in platinum and DWCNT-based DSCs are analyzed and discussed. The catalytic activity and DSC performance of DWCNTs and Pt are compared. A conversion efficiency of 6.07% has been obtained for DWCNT counter-electrode DSCs. This efficiency is comparable to that of platinum counter-electrode-based devices.

Titanium dioxide nanotubes were directly fabricated from commercial P25 TiO2 via alkali hydrothermal transformation. The prepared titanate nanotubes were successfully used as an electrode material for dye-sensitized solar cells (DSCs). A metal-free organic dye (indoline dye D102) was used as a sensitizer. The used indoline dye D102 is of high purity (⩾98%) and high absorption coefficient (67,500 L mol−1 cm−1 at 501 nm). The TiO2 pastes were prepared with PEG (Mw 20,000) and as-made TiO2 nanotubes or P25 powders. Titania thin films were grown by screen printing method. High conversion efficiencies of light to electricity of around 9.8% and 7.6% under illumination of simulated AM1.5 sunlight (100 mW/cm2) were achieved with P25 and TiO2 nanotube cells, respectively. The fill factor of DSCs based on TiO2 nanotubes increased in comparison with that of DSCs based on TiO2 nanoparticles. The electron transport and dye adsorption properties in both titanate nanotube and P25 electrodes were evaluated in terms of photovoltaic characteristics of the fabricated cells. The related mechanisms were discussed. The study provides a promising method for the development of high-efficiency and low-cost DSCs.

Indium tin oxide (ITO) films were grown without external heating in an ambient of pure argon by RF-magnetron sputtering method. The influence of argon ambient pressure on the electro-optical properties of as-deposited ITO films was investigated. The morphology, structural and optical properties of ITO films were examined and characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM) and UV–VIS transmission spectroscopy. The deposited ITO films with a thickness of 300 nm show a high transparency between 80% and 90% in the visible spectrum and 14–120 Ω/□ sheet resistance under different conditions. The ITO films deposited in the optimum argon ambient pressure were used as transparent electrical contacts for thin film Cu(In,Ga)Se2 (CIGS) solar cells. CIGS solar cells with efficiencies of the order of 7.0% were produced without antireflective films. The results have demonstrated that the developed ITO deposition technology has potential applications in thin film solar cells.

InGaN/GaN multi-quantum well (MQW) light-emitting diodes (LEDs) with indium tin oxide (ITO) as widow layers were fabricated. The ITO surface was textured utilizing the natural lithography combined with the inductively coupled plasma (ICP) etching technology by use of polystyrene spheres as the etching mask. The morphologies of the textured ITO surface were characterized by a scanning electron microscope (SEM) and an atomic force microscope (AFM). The electrical and optical properties of surface-textured ITO/GaN LEDs were measured and analyzed. The influence and dependence of ICP etching time on the light output of the fabricated LEDs was investigated. Experimental results indicated that ITO/GaN LEDs with nano-islands with a depth of about 120 nm and a diameter about 320 nm on the surfaces exhibited a ∼60% or more enhancement in the output power. The typical 20 mA driven forward voltage is only 0.2 V higher than that of conventional planar ITO/GaN LED. The fabricated surface-textured GaN LED chips from the whole 2″ wafer presented a quite good conformance in electrical and optical characteristics, and the proposed method demonstrated a good reliability. The results indicate that the surface-textured ITO method utilizing the natural lithography combined with the inductively coupled plasma (ICP) etching technology has high potential in future large-area high-power GaN LED applications.

InGaN/GaN multi-quantum well (MQW) light-emitting diodes (LEDs) with indium tin oxide (ITO) and Ni/Au p-contacts were fabricated. ITO (500 nm) and Ni/Au (2 nm/9 nm) films were deposited onto p-GaN epitaxial layers by an e-beam evaporation system. For the LEDs using in situ annealed ITO and Ni/Au films as p-contacts, the forward voltage at 20 mA was 3.5 and 3.2 V, respectively. Under the same amount of injection current, the LED with in situ annealed ITO p-contact had higher output electroluminescence (EL) intensity and larger light output power. The EL intensities and the light output power of ITO LEDs were enhanced by 85% and 60%, respectively, at 20 mA. As a result, the light output and power conversion efficiency of ITO LEDs on GaN were greatly improved at high injection currents. The fabricated LEDs were subjected to a stress test at 30 mA and 55 °C and showed a very small degradation of optical power (<1% decrease) for 24 h. The light output of MQW LEDs keeps 80% of the original value after 1000 h stressing. Therefore, the fabricated LED devices have demonstrated a good reliability.

We have investigated the phase transformations induced in a Ge1Sb2Te4 system by a femtosecond laser exposure. The system has a multilayer structure of 10 nm ZnS–SiO2/(10–100 nm) Ge1Sb2Te4/80 nm ZnS–SiO2/0.6 mm polycarbonate substrate. The morphology and contrast of marks written in both amorphous and crystalline backgrounds by single fs pulses were characterized using an optical microscope. X-ray diffraction was applied to identify the crystal structures formed by single 108 fs shots. The characteristics and the conditions of crystalline → amorphous or amorphous → crystalline transitions in the multilayer structures with different Ge1Sb2Te4 layer thickness triggered by single shots were investigated. The pulse energy window for the crystallization or amorphization in the Ge1Sb2Te4 systems was established. The mechanism of phase changes triggered by femtosecond laser pulses is discussed.