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Tremendous progress has been made in power conversion efficiency (PCE) of thin-film photovoltaics over the past few years, yet most current high-efficient photoactive layer usually contains rare or toxic elements accompanied by expensive and complicated vacuum processes, which increases the cost and limits the scope of the applications in the long run. Here we present a synergistic effect of quantum effect of an earth-abundant and low toxic ultrafine Cu2ZnSnS4 (CZTS) quantum dots (QDs) and low charge recombination in one dimensional TiO2 nanotube arrays for optoelectronic devices. By ligands exchange, the as-obtained ultrafine CZTS QDs have been robustly anchored to a highly ordered TiO2 nanotube arrays (TNAs) to be served as a function layer in a simple QDs sensitized solar cells. Such ultrafine CZTS QDs based solar cells exhibit significant enhancement up to 457% in PCE compared to that of CZTS QDs with larger size. The CZTS QDs functionalized TNAs has also shown excellent charge transport capability with lower recombination rate than QDs sensitized TiO2 nanoparticles and it is expected to be used as a low-cost environment-friendly function layer for various potential optoelectronic applications.

Broadband emission of 1400–2100 nm is achieved in Er–Tm codoped ZnO (ETZO) films at an excitation of photon energies higher than the band gap of ZnO. Room temperature (RT) and temperature-dependent...

An amorphous silica layer containing Mo component (a-SiOx(Mo) ∼ 3.5–4.0 nm) is naturally formed in the process of evaporating MoO3 power onto n-type silicon, which plays a significant role on the non-equilibrium carriers’ transport of MoOx/n-Si heterojunction photovoltaic device. The electronic structure and the charge transition levels of the amorphous silicon oxide doped with Mo are derived from density functional theory. The density of states show that the five local states are existed in the band gap of amorphous silicon oxide, caused by the hybridization of Mo 4d orbital and O 2p orbital. The charge transition level of e(+1/0) is located at 3.59 eV above the valance band maximum of a-SiO2, which could be a passageway of holes produced in the opto-electric conversion. Defects level-assisted quantum transport mechanism is put forwarded to explain hole transport phenomenon in the MoOx/SiOx(Mo)/n-Si PV device.

There is no doubt that silicon-based solar cells provide continuous power to space vehicles, but exposure to high-energy particle irradiation and large temperature differences are two challenges. In this report, the temperature effects of the crystalline silicon-based solar cells are experimentally evaluated by the short-circuit current and open-circuit voltage at a scope of 10-300K. The test PV device is named as semiconductor – quasi – insulator - semiconductor (SQIS), which is fabricated by a direct sputtering deposition of ITO film on crystal Si substrate clad with reactive grown a-SiOx(In), an indium-contained hybrid oxide layer.

A black phase CsPbI2Br film was prepared by mesophase transformation strategy in air atmosphere, and a methylamine acetate vapor-assisted annealing method was applied. The CsPbI2Br film exhibits a ...

Molybdenum oxide (MoO

In this report, a numerical simulation for ITO/n-Si based hetero-junction (ISHJ) photovoltaic device has been carried out by using AFORS-HET software and a proper model, in which the naturally derived interface layer with a ternary-like hybrid of a-SiOx(In) is assumed to be a double stacks of 1.2 nm quasi p type semiconductor and 0.2 nm insulator as buffer layer. The negative charge centers, in the range of >1 × 1017 cm−3, associated with oxygen vacancies and indium-ion correlative ternary hybrid in the intermediate region play multi-roles, including field effect passivation, inducing inversion layer and acting selective contacts to a certain extent. The simulation results manifest that the intermediate region behaviors as a semiconductor material with a wide band gap of 2.06 eV, which is suitable for the transport of hole and an induced quasi p-n junction. Additionally, the simulated J-V curve arisen from the key opto-electric parameters of the device by the simulation agrees with the experimental one with a high fill factor of 74.2% well.

The promising n-Si-based solar cell is constructed for the purpose of realizing hole- and electron-selective passivating contact, using a textured front indium tin oxide/MoO x structure and a planar rear a-SiO x/poly(Si(n+)) structure severally. The simple MoO x/n-Si heterojunction device obtains an efficiency of 16.7%. It is found that the accompanying ternary hybrid SiO x(Mo) interlayer (3.5-4.0 nm) is formed at the MoO x/n-Si boundary zone without preoxidation and is of amorphous structure, which is determined by a high-resolution transmission electron microscope with energy-dispersive X-ray spectroscopy mapping. The creation of lower-oxidation states in MoO x film indicates that the gradient distribution of SiO x with Mo element occurs within the interlayer, acting as a passivation of silicon substrate, which is revealed by X-ray photoelectron spectroscopy with depth etching. Specifically, calculations by density functional theory manifest that there are two half-filled levels (localized states) and three unoccupied levels (extended states) relating to Mo component in the ternary hybrid a-SiO x(Mo) interlayer, which play the roles of defect-assisted tunneling and direct tunneling for photogenerated holes, respectively. The transport process of photogenerated holes in the MoO x/n-Si heterojunction device is well-described by the tunnel-recombination model. Meanwhile, the a-SiO x/poly(Si(n+)) has been assembled on the rear of the device for direct tunneling of photoinduced electrons and blocking photoinduced holes.

The large area and high-quality two-dimensional molybdenum disulfide (2D-MoS2) film has been synthesized by a modified single-zone chemical vapor deposition technique. The influence of gas environment, reaction temperature and gap distance (between MoO3 precursor and substrate) on 2D-MoS2 growth were systematically investigated. A stable gas environment was prerequisite for the formation of 2D-MoS2, and it can be achieved by adjusting the pressure and flow rate of N2 in the furnace tube, which was numerical estimated via Antoine equation. The thickness, quality (uniformity and crystallinity), roughness, and chemical composition of the MoS2 nano-film were characterized by the optical microscopy, scanning electron microscope, Raman spectroscopy, Atomic force microscope, and X-ray photoelectron spectroscopy, respectively. The results showed that the quality of MoS2 nano-film was greatly influenced by the nucleation density on the substrate, which could be controlled by modulating the reaction temperature and gap distance. Moreover, a “frustum-like” model was established to match the practical reaction situation and clarify the internal relationship among reaction temperature, gap distance and the nucleation density of MoS2 film. Finally, a high-quality monolayer MoS2 nano-film, at 800 °C with a gap distance of 3.5 mm, was obtained and verified by experimental and numerical analyses.

The tin-doped indium oxide (ITO) and the intermediate nanometer-scale SiO x layers were synthesized directly on n-type crystalline silicon (n-Si) substrate by radio-frequency magnetron sputtering deposition. During the ITO-sputtering deposition, the effect of shallow implantation intermixing led to forming an ultra-thin SiO x layer, which could successfully lessen the interface states and promote the transportation of carriers. The photovoltaic properties of devices showed the open-circuit voltage ( V oc ) strongly correlated to the carrier concentration of ITO ( n ITO ), indicating a hole-selective contact of ITO. An equivalent “p-type Fermi level” (hole as majority carriers) was reasonably employed to interpret the decrease of V oc with the increase of n ITO . The impact of the work function difference between ITO and n-Si on V oc of ITO/SiO x /n-Si heterojunction cells was tentatively equivalent to the difference of the defined quasi-Fermi levels. Through the modification of surface-reflectance and rear contact, the heterojunction structure solar cells achieved efficiency of 11.50 ± 0.17%. Furthermore, the stability of the devices in conversion efficiency was excellent over a whole year. The temperature coefficient of −0.34%/°C was obtained, which was better than −0.45%/°C of a typical diffused-junction silicon solar cell.

On the basis of a photon-assisted high frequency capacitance–voltage ( C – V ) method (1 MHz C – V ), an effective approach is developed to evaluate the average interface state density ( D it ) of an ITO–SiO x /n-Si heterojunction structure. Tin-doped indium oxide (ITO) films with different thicknesses were directly deposited on (100) n-type crystalline silicon by magnetron sputtering to fabricate semiconductor–insulator–semiconductor (SIS) hetero-interface regions where an ultra-thin SiO x passivation layer was naturally created. The morphology of the SiO x layer was confirmed by X-ray photoelectron spectroscopy depth profiling and transmission electron microscope analysis. The thinness of this SiO x layer was the main reason for the SIS interface state density being more difficult to detect than that of a typical metal–oxide–semiconductor structure. A light was used for photon injection while measuring the C – V of the device, thus enabling the photon-assisted C – V measurement of the D it . By quantifying decreases of the light-induced-voltage as a variation of the capacitance caused by parasitic charge at interface states the passivation quality within the interface of ITO–SiO x /n-Si could be reasonably evaluated. The average interface state density of these SIS devices was measured as 1.2–1.7 × 10 11 eV −1 cm −2 and declined as the passivation layer was made thicker. The lifetime of the minority carriers, dark leakage current, and the other photovoltaic parameters of the devices were also used to determine the passivation.

The SIS (semiconductor-insulator-semiconductor) structure heterojunction derived from the MOS (metal-oxide- semiconductor) devices, and inherit the advantages of low cost, simple structure, stable performance and high theoretical efficiency, which drew tons of attention for solar cell and integrated circuit applications researches. SIS device consist of TCO (transparent conduction oxide) layer, ultra-thin oxide layer and silicon substrate, in which the carriers can tunnel through the oxide layer when the thickness of the interface oxide layer is reduced to 1–5 nm. Inside the SIS solar cell, the ultra-thin passivation layer has multiple functions including tunneling contact and buffer the crystalline lattice mismatch. Capacitance reflects a device’s ability to charge and discharge, and the capacitance voltage ( CV ) characteristic is critical in the estimate of the passivation quality no matter in the high-low frequency method or DLTS (deep level transient spectroscopy system) method, and the passivation quality manifest as interface state density ( D it). When examining the high frequency (1 MHz) CV characteristic of the SIS which was fabricated by depositing ITO upon n-type silicon directly by RF magnetron sputtering, it is found that once the applied voltage ( V g) exceeds a certain value V T (tunneling voltage), the differential capacitance value of the device would far beyond the range of the instrument and tends to infinity, which can be summarized as tunnel capacitance overload phenomenon (TCOP). As the description and explanation of this phenomenon have not been found in previous studies, the high-frequency TCOP of the SIS heterojunction with ultra-thin interfacial layers was investigated in details in this paper. The current-voltage characteristics of the SIS devices were obtained from the solar simulator and shown good photovoltaic conversion efficiency. The built-in electric field of the SIS with different ITO thickness was obtained by fitting the CV curves, which was measured by the Keysight E4980A CV system. The XPS depth profiling showed that the composition and percentage content of the interface, including In, Sn, O, Si, and the oxide silicon compound of Si2O, SiO, Si2O3, SiO2 which can be summed as SiO x (1≤ x ≤2). The TEM images showed that the thickness of the SiO x layer increases with the thickness of ITO layer, and the V T in TCOP is apparently linked to the SiO x thickness. When the applied V g exceed V T, a huge amount of electrons would enter the E C of the silicon surface, unlike the MOS with thick and well passivated insulator layer, the ultra-thin SiO x layer can’t hold these mass of electrons at the SIS interface, so the electrons would directly tunnel through the SiO x into the ITO layer and the TCOP appears. Capacitance voltage characteristics are critical for estimating the properties of heterojunction interfaces, and high frequency CV is indispensable for measuring the D it. The existence of the TCOP is the main reason why other methods which based on the CV characteristics are difficult to estimate the interface state. But from another point of view, the TCOP is repeatable in the same device, which implied that the solar cells that fabricated by the directly depositing ITO thin films on n-type silicon is stable.

In this article, using controllable magnetron sputtering of indium tin oxide (ITO) materials on single crystal silicon at 100 °C, the optoelectronic heterojunction frame of ITO/a-SiOx(In)/n-Si is simply fabricated for the purpose of realizing passivation contact and hole tunneling. It is found that the gradation profile of indium (In) element together with silicon oxide (SiOx/In) within the ultrathin boundary zone between ITO and n-Si occurs and is characterized by X-ray photoelectron spectroscopy with the ion milling technique. The atomistic morphology and physical phase of the interfacial layer has been observed with a high-resolution transmission electron microscope. X-ray diffraction, Hall effect measurement, and optical transmittance with Tauc plot have been applied to the microstructure and property analyses of ITO thin films, respectively. The polycrystalline and amorphous phases have been verified for ITO films and SiOx(In) hybrid layer, respectively. For the quantum transport, both direct and def...

A silicon based ternary compound was supposed to be solid synthesized with In, Si and O elements by magnetron sputtering of indium tin oxide target (ITO) onto crystal silicon substrate at 250 °C. To make clear the configuration of the intermediate region, a potential method to obtain the chemical bonding of Si with other existing elements was exploited by X-ray photoelectron spectroscopy (XPS) instrument combined with other assisted techniques. The phase composition and solid structure of the interfacial region between ITO and Si substrate were investigated by X-ray diffraction (XRD) and high resolution cross sectional transmission electron microscope (HR-TEM). A photovoltaic device with structure of Al/Ag/ITO/SiOx/p-Si/Al was assembled by depositing ITO films onto the p-Si substrate by using magnetron sputtering. The new matter has been assumed to be a buffer layer for semiconductor-insulator-semiconductor (SIS) photovoltaic device and plays critical role for the promotion of optoelectronic conversion performance from the view point of device physics.

The temperature dependence of initial transient current-voltage (I-V) characteristic of planar perovskite solar cell by one-step solution process is investigated. An S-shaped I-V characteristic emerges in response to low temperature and the photovoltaic parameters drop dramatically. This is mainly attributed to the increasing amount of negative charges accumulating in the TiO 2 /CH 3 NH 3 PbI 3 interface region and the reduced built-in field separating the photo-generated carriers in the absorber layer. The influence of negative charge accumulation can be represented by two extra diodes that are in series with a conventional solar cell circuit model at low temperature whereas it acts as a resistor with low resistivity above room temperature. These findings help to understand the charge transport mechanism in perovskite solar cells.

Plasma enhanced chemical vapor deposition (PECVD) is one effective method to prepare graphene at low temperature in a short time. However, the low temperature in PECVD could not provide substrate a proper state for large area and few layer graphene preparation. Herein, we propose a two-step method to grow graphene on Cu foils. In the first step, in order to acquire a smooth and oxide-free surface state, methanol was used as a reductant to pretreat Cu. In the second step, graphene films were prepared on Cu foils by PECVD using CH 4 as carbon source with H 2 -free. Few-layer graphene sheets with diameter about 1 μm under low temperature (700 °C) and at a short time (10 min) on well pretreated Cu foils were successfully gotten. The effect of methanol pretreatment on graphene synthesis and the graphene growth mechanism on Cu substrate by PECVD are analyzed comprehensively.

For the purpose of introducing a high work-function layer to improve the implied voltage in asymmetric silicon-based heterojunction (SHJ) photovoltaic device, molybdenum oxide (MoOx, 0≤x≤3) has been applied to the system. However, besides the role of extracting hole on one side, another singularity behavior presented in the nonequilibrium state, i.e., worsen photovoltaic feature ("S-shape") of current density-voltage (J-V) was revealed with an inappropriate chemical state of the MoOx film. The source of "S-shape" behavior of MoOx/a-Si: H(i)/n-Si heterojunction device was co-analyzed by X-ray photoelectron spectroscopy (XPS) with depth profiling, ultraviolet photoelectron spectroscopy (UPS), current density-voltage representation, minority carrier lifetime survey and AFORS-HET software simulation. It was found that an amorphous SiOx interlayer was spontaneously formed during deposition of MoOx film onto a-Si: H(i)/n-Si substrate, blocking transport of holes. The decreases in work-function of MoOx layer are attributed to oxidation reaction at MoOx/a-Si: H(i) boundary zone, which results in the decline of holes selectivity. A rising O/Si ratio of SiOx interlayer induces an augment of valence band offsets, which could be used to mainly interpret the "S-shape" response because of a barrier that hinders thermionic emission of holes. Meanwhile, the thicker (>4 nm) SiOx layer leads to a lower tunneling probability of holes. The characteristic analysis of the MoOx/a-Si: H(i)/n-Si heterojunction device deepens understanding for hole transport mechanism of the device.

The promising n-Si-based solar cell is constructed for the purpose of realizing hole- and electron-selective passivating contact, using a textured front indium tin oxide/MoO

It is assumed that a ternary indium-doped amorphous silicon oxide layer (In-Si-Ox) has been produced during RF magnetron sputtering growth of indium tin oxide (ITO) film directly on crystalline silicon substrate. Its chemical components and thickness were determined by X-ray photoemission spectroscopy (XPS) in depth profile and cross-section transmission microscope (TEM), respectively. The functional properties of the buffer layer materials have been manifested by its photovoltaic feature, by which an inversion layer near silicon bulk was induced and tunneling path of hole through which a high filled factor is obtained with a better rectified I-V characteristic and photovoltaic (PV) conversion.

During fabrication of TCO/SiO x /n-Si (SIS) photovoltaic devices, deposition of TCO films by sputtering damages the electronic structure of the SiO x /c-Si interface, leading to higher interface recombination rate and lower open circuit voltage of the obtained photovoltaic device. Enhancing the interface recombination rate is equivalent to decreasing the diffusion length in the bulk and reducing the short circuit current. It is obvious that damage to the interface can seriously affect the overall performance of the device. Usually, researchers are only concerned with the effect of passivation before TCO film deposition by sputtering, or with the overall performance of the fabricated device; thus, the damage incurred by sputtering during device fabrication is often overlooked. The damage incurred by sputtering on the efficient silicon-based heterojunction solar cells, especially the SIS devices, is rarely considered. In this letter, we report the investigations of the damage incurred by the energetic particle beams in the plasma (atoms/ions and UV glow) on the atomic bonding and electronic states in both ultra-thin silicon oxides and SiO x (1.5-2.0 nm)/c-Si(150 μm) samples interface. The analysis was performed by using vacuum thermal annealing, effective minority carrier lifetime measurements (by using μ-PCD), and surface X-ray photoemission spectroscopy (XPS). The damage was observed in the process of magnetron sputtering deposition of the ITO thin film. We also investigated the effective passivation function of the ITO thin films silicon surface. The results show that the samples lifetime was reduced by more than 90% (from 105 μs to 5 μs) after the sputtering deposition of the ITO thin film. However, vacuum annealing at 100-400°C for 30 min partially eliminated the damage to the SiO x /c-Si interface and improved the passivation effect of the thin oxide layer on the crystalline silicon. Vacuum annealing at 200°C for 30 min restored the lifetime to nearly 30 μs; this annealing temperature corresponds to the typical temperature for the preparation processes of most efficient crystalline silicon heterojunction photovoltaic devices. However, vacuum annealing at 500-700°C for 30 min yielded a lifetime of about 3 μs. The analysis performed by comparing the results of XPS depth profiling revealed that the gaseous unstable material SiO is generated at the SiO x /c-Si interface under this annealing condition, which damages the SiO x /c-Si interface and augments the unsaturated bond silicon oxide SiO x (0 x

Few layer graphene were synthesized on different substrates by radio frequency plasma enhanced chemical vapor deposition in the absence of any catalyst under 300 °C. Raman spectral characterization verified the bonding form of the films to be mostly sp 2. The principal chemical mechanisms relevant to the growth of graphene from gaseous hydrogen and hydrocarbon species are presented. The kinetic processes during the activation and transport of the gaseous species are described. Furthermore, the effects of substrate treatment in the course of growth are analyzed. We demonstrated that the differences in growth conditions reveal different mechanisms of growth of graphene by chemical vapor deposition. Nevertheless, the overall thermodynamic and dynamics principles are identical. It is reasonable to obtain few layer graphene films by using methane alone without H2 as source gas. Moreover, graphene films of various feature and structures for different purposes can be achieved controllably by modulating the kinetic factors. Also, these graphene films can be used in many photoelectric devices such as solar cells and photodetectors.

Averaged over wavelength range from 500 to 1600 nm at normal incidence, the reflection losses of silicon wafer as master mold are reduced from original 35% to only 0.2% after integrating surface moth-eye structures, and glass slide suppresses the reflection from 7.5% to near 0.4% after incorporating polymer-based moth eyes on double side by replica molding that enables transferring moth eyes from master mold of silicon onto any substrate. An outstanding anti-reflective property out to large incident angles is realized with the average reflection below 0.5% until 50°, below 2.5% at 60° and below 7.5% at 70°, which holds promise for solar cell application.

In this article, using controllable magnetron sputtering of indium tin oxide (ITO) materials on single crystal silicon at 100 °C, the optoelectronic heterojunction frame of ITO/a-SiO

The chlorine-based organometallic halide perovskite (Cl-OHP) film with a (001)-preferred orientation and good crystallization has been synthesized by a hybrid sequential deposition process. The photoluminescence and absorption spectra of the Cl-OHP film in the blue light region have been investigated at operating temperatures ranging from 10 to 350 K. The Cl-OHP film shows a strong exciton-related emission of which the exciton binding energies at low temperature and high temperature are 136 meV and 41 meV, respectively. It is found that the blueshift from excitonic luminescence is initially observed at temperature below 175 K, and then, the redshift occurs from 175 to 350 K. Meanwhile, the bandgap of the Cl-OHP film widens with the increase in operating temperature. The nonmonotonous shifts on the emission peak energy are attributed to the competition between the Stokes effect and bandgap widening. This should contribute to the understanding of photophysical processes in Cl-OHP materials and devices.

In order to methodically investigate the influence of sputtering power on interface states and performance of ITO/a-SiOx/n-Si device, the indium-tin oxide film (ITO) with thickness of 80 nm, was deposited on n-type silicon substrate by radio frequency magnetron sputtering. The device photovoltaic (PV) performance and the interface states of ITO/n-Si system were measured by solar simulator measurement system and the light-assisted high frequency capacitance-voltage (C–V) method, respectively. The experimental results demonstrate that the PV parameters of the ITO/a-SiOx/n-Si device achieve optimal values of PV parameters at 120 W (Voc~0.45 V, Jsc~28.57 mA/cm2, FF~71.20%, η~9.63%). Especially, the average interface state density (Dit) of ITO/n-Si interface drops from (1.29 ± 0.05) to (1.04 ± 0.02) × 1011 cm−2eV−1 when the sputtering power increases to 120 W, but the Dit sharply rises at higher sputtering power, which is negatively correlated with Voc and η. The effective minority carrier lifetime and O/Si ratio within interfacial layer were characterized by μ-PCD instrument and X-ray photoelectron spectroscopy, respectively. It is found that the device is well passivated by a-SiOx at 120 W. Moreover, the device performance is well-associated with the interface states and sputtering power.

Carbon films with the thicknesses varying from 10 to 600 nm in the architecture range of carbonaceous graphene to graphitic bonding were synthesized on Si wafer. The films were prepared by radio frequency plasma enhanced chemical vapor deposition under 300 °C without any catalyst and hydrogen-assistant ambient as well. The films found to be composed of microcrystalline graphene and graphite inclusions with a maximum graphene film size of 2 µm. Raman spectral characterization verified the bonding form of the graphene–graphitic films to be mostly sp2. In this work, the complicated transfer printing process for carbon/silicon (C/Si) devices and the quality degradation of the hybrid films were avoided by the direct deposition of the carbonaceous films on Si substrate. The current–voltage feature of the devices manifested that the devices possess an excellent rectifying behavior in dark and the characteristic of photovoltaic in the illumination (known as solar cells).

In the paper, the effect of rapid thermal annealing on non-optimal double-graded band gap profiles was investigated by using X-ray photoelectron spectroscopy and capacitance–voltage measurement techniques. Experimental results revealed that proper rapid thermal annealing treatment can effectively improve band gap profile to more optimal level. The annealing treatment could not only reduce the values of front band gap and minimum band gap, but also shift the position of the minimum band gap toward front electrode and enter into space charge region. In addition, the thickness of Cu(InGa)Se 2 thin film decreased by 25 nm after rapid thermal annealing treatment. All of these modifications were attributed to the inter-diffusion of atoms during thermal treatment process. Simultaneously, the variation of the band gap profile created an absolute gain in the efficiency by 1.22%, short-circuit current density by 2.16 mA/cm 2 and filled factor by 3.57%.

In this paper, the recombination through defects in absorber and CdS/Cu(In,Ga)Se 2 interface states has been investigated by comparing photoluminescence to electroluminescence. The ranges of photoluminescence and electroluminescence collection region are 450 and 90 nm, respectively. Thus, electroluminescence is more sensitive to CdS/CIGS interface recombination than photoluminescence. The devices experienced rapid thermal annealing at the temperature of 300 °C. After annealing, the reduction of In Cu defects in absorber layer increased PL and EL intensities at +0.7 V bias by three times, while the decrease of interface states increased EL intensities from +1.0 to +1.5 V bias by six times. The capacitance–voltage characterization confirmed that the density of interface states fell from 2.8×10 13 to 1.5×10 13 cm −2 .

Highly ordered, vertically aligned TiO 2 nanotube arrays (TNAs) have been prepared by a modified two-step anodic oxidation. The second as-prepared TNAs show smoother surface, fewer cracks and more uniform nanotubes on large scale compared with the first as-grown one. With different content of water in anodizing electrolyte, highly oriented TNAs and arbitrarily oriented TNAs were obtained. The narrow dominant peak of (004) of XRD shows that the TNAs are highly crystallized. Moreover, the interplanar distance of 0.237 nm, the marked angle in fast Fourier transform of 68.3° and the diffraction fringe on the margin of tube wall by high-resolution transmission electron microscopy demonstrate that the highly oriented TNAs are single-crystal-like anatase in nature with highly exposed (001) facets which grow along the [001] direction. The TNAs have been detached and transferred to Fluorine-doped Tin Oxide substrate successfully as transparent photo-anodes for assembling dye-sensitized solar cells. Under front-side illumination, DSSCs based on highly [001] oriented TNAs show a remarkable enhancement of 29% in power conversion efficiency and faster electron transport compared to that of arbitrarily oriented TNAs. The influence of the thickness on the performance of the DSSCs based on highly [001] oriented TNAs is investigated and the best power conversion efficiency of 5.73% is achieved.

In this paper, a series of recombination paths in Al:ZnO/ZnO/CdS/Cu(In,Ga)Se2 (CIGS) solar cell has been carried out through photoluminescence (PL) emission, optoelectronic conversion characteristic and AFORS HET simulation. Proper rapid thermal annealing (RTA) lead to the improvement of CIGS performance by reducing bulk recombination of CIGS layer and interface recombination, which opens the way to explore a useful method to significantly ameliorate the microstructure within the CIGS layer. A maximum value for the conversion efficiency was obtained when the annealing temperature was continuously increased to 400 °C, where the efficiency increased by 43%, and the recombination from the interface states, the bulk defect traps and the tunneling enhancement recombination was reduced to the lowest. The opto-electronic parameters, such as short-circuit current Jsc, open-circuit voltage Voc, reverse saturation current J0 and the series resistance Rs have been correlatively investigated to the nonradiative transition among the various defects and are strongly dependent upon the annealing temperature as well.

The novel ITO/AZO/SiO2/p-Si SIS heterojunction has been fabricated by low temperature thermal oxidation an ultrathin silicon dioxide and RF sputtering deposition ITO/AZO double films on p-Si (1 0 0) polished substrate. The microstructural, optical and electrical properties of the ITO/AZO antireflection films were characterized by XRD, SEM, UV–VIS spectrophotometer, four point probe and Hall effect measurement, respectively. The results show that ITO/AZO films are of good quality. And XPS was carried out on the ultrathin SiO2 film. The heterojunction shows strong rectifying behavior under a dark condition, which reveals that formation of a diode between AZO and p-Si. The ideality factor and the saturation current of this diode is 2.7 and 8.68 × 10−5 A, respectively. High photocurrent is obtained under a reverse bias when the crystalline quality of ITO/AZO double films is good enough to transmit the light into p-Si. We can see that under reverse bias conditions the photocurrent of ITO/AZO/SiO2/p-Si SIS heterojunction is much higher than the photocurrent of AZO/SiO2/p-Si SIS heterojunction. Because the high quality crystallite and the good conductivity of ITO film which prepared by magnetron-sputtering on AZO film lead to a great decrease of the lateral resistance. The photon induced current can easily flow through ITO layer entering the Cu front contact. Thus, high photocurrent is obtained under a reverse bias.

A sort of ITO/SiO2/n+p configuration of solar grade silicon - based SINP device has been successfully fabricated by coupling high quality of indium tin oxide (ITO) thin film and ultra-thin silicon dioxide buffer layer on the p-n junction, which showed a potential to improve the short-circuit current density (JSC) as well as the conversion efficiency. The progress to avoid the use of last two processes with PECVD and high temperature firing in the normal production for the crystal silicon solar cell may be a way toward the low cost and the high efficiency. In addition, the tunneling hypostasis of carriers is present in the device.

Uniform, debris-free, fewer-crack, and highly ordered TiO 2 nanotube arrays are prepared by a two-step anodic oxidation method, and a surfactant-assisted vacuum impregnation approach is developed to control the incorporation of sub-10-nm TiO 2 nanocrystals into the nanotube arrays. By using the double polymer surfactants of polyethylene glycol and Polyvinyl Pyrrolidone as a sacrificed template, nanocrystal over-agglomeration is prohibited, and thin nanocrystal mesoporous layers are formed on both inner and outer nanotube walls. The application of the nanocrystal filled nanotube arrays as the photoanode for dye-sensitized solar cells has been evaluated. The incorporation of the nanocrystals into the nanotube arrays is found to enhance dye absorption and light-harvesting capacities markedly. As a result, the solar cells based on the filled nanotube arrays hold a short-circuit current density 2.06 times and a power-conversion efficiency 1.94 times higher than those based on the unfilled nanotube arrays.

Nano-porous silicon (NP-Si) and nano-inverted-pyramid silicon (NIP-Si) structures have been formed by Ag-catalyzed chemical etching without and with NaOH modification on solar-grade multi-crystalline silicon substrates, respectively. The influence of nano-structured morphology (NSM) and SiNx layer (SL) on effective reflectance (Reff) has been investigated through measurement and simulation. For typical NP-Si and NIP-Si samples, the NSM alone can suppress Reff of NP-Si sample to the lowest degree (5.87%), and the combination of NSM and SL is favorable to gain the lowest optical loss for NIP-Si sample (Reff = 7.31%). Compared with NP-Si solar cell, the fabricated NIP-Si solar cells have hugely improved photovoltaic properties, resulting from reduced reflectance in visible and near-infrared wavelength, enhanced short-wavelength spectral responses and good diode parameters. Finally, an optimum design strategy of NSM and SL has been suggested to gain potentially better properties for nano-structured solar cells.

Amorphous indium-tin-oxide (a-ITO) film was deposited by radio-frequency (RF) magnetron sputtering at 180°C substrate temperature on the texturized p-Si wafer to fabricate a-ITO/p-Si heterojunction solar cell. The microstructural, optical and electrical properties of the a -ITO film were characterized by XRD, SEM, XPS, UV-VIS spectrophotometer, four-point probe and Hall effect measurement, respectively. The electrical properties of heterojunction were investigated by I–V measurement, which reveals that the heterojunction shows strong rectifying behavior under a dark condition. The ideality factor and the saturation current density of this diode are 2.26 and 1.58×10−4 A cm−2, respectively. And the value of IF/IR (IF and IR stand for forward and reverse currents, respectively) at 1 V is found to be as high as 21.5. For the a-ITO/p-Si heterojunction solar cell, the a-ITO thin film acts not only as an emitter layer, but also as an anti-reflected coating film. The conversion efficiency of the fabricated a-ITO/p-Si heterojunction cell is approximately 1.1%, under 100 mW cm−2 illumination (AM1.5 condition). And the open-circuit voltage (Voc), short-circuit current density (JSC), filll factor (FF) are 280 mV, 9.83 mA cm−2 and 39.9%, respectively. Because the ITO film deposited at low temperature is amorphous, it can effectively reduce the interface states between ITO and p-Si. The barrier height and internal electric field, which is near the surface of p-Si, can effectively be enhanced. Thus we can see the great photovoltaic effect.

A novel method was proposed to form porous silicon (PS) antireflection layers and thin SiO2 films at the same time by HF/H2O2 treatment of acid-textured pn+ multicrystalline silicon. Porous silicon structures formed inside the cavities and the porosity became large with an increase of the treated time resulting in a dramatical decrease of reflectance. The reflectance decreased to less than 5% within the wavelength range of 420-970 nm after 5 min HF/H2O2 treatment. Furthermore, the minority-carrier lifetime showed an increase of about 42% for a short treated time because of the formation of a thin silicon oxide layer resulting the reduction of dangling silicon bonds in the interface between PS/Si.

The structural and mechanical factors that control the torsion fracture behavior of cold-drawn eutectoid steel wires are examined. Two types of the fracture are identified; namely, flat- and cleavage-type. Torsion cracks are found to initiate in ferrite and propagate along the ferrite/cementite interface. The shear stress distribution within the wires is affected not only by the applied torque, but also by the residual stress. The maximum shear stress occurs halfway from center to the surface, where the cracks initiated. The growth of torsion cracks is sensitive to the orientation of cementite lamellas in pearlite grains. The influence of thermal history on the occurrence of cleavage fracture is ascertained, with the assistance of atom probe. It shows that the cleavage fracture results from a decrease in dislocation mobility, caused by thermally activated diffusion of carbon atoms into ferrite.

Nanoporous black silicon (nb–Si) structures with/without saw damage removal (SDR) on solar-grade multi-crystalline silicon substrates have been formed by simple Ag-induced chemical etching. The nb–Si shows a unique morphology of nano-scale holes on micron-scale patterns with low reflectance (

Silver nanowires (AgNWs) networks are promising candidates for the replacement of indium tin oxide (ITO). However, the surface roughness of the AgNWs network is still too high for its application in optoelectronic devices. In this work, we have reduced the surface roughness of the AgNWs networks to 6.4 nm, compared to 33.9 nm of the as-deposited AgNWs network through the hot-pressing process, treatment with poly (3,4ethylenedioxythiophene)–poly (styrenesulfanate), and covered with graphene films. Using this method, we are able to produce AgNWs/PEDOT: PSS/SLG composite films with the transmittance and sheet resistance of 88.29% and 30 Ω/□, respectively. The OLEDs based on the AgNWs/PEDOT: PSS/SLG anodes are comparable to those based on ITO anodes.

The effect of rapid thermal annealing (RTA) on the compositional ratio of atoms and interfacial zone of Cu(In,Ga)Se 2 (CIGS) solar cells was systematically studied using X-ray photoelectron spectroscopy. The RTA treatment induced the diffusion of Al, Zn, and Se atoms, which increased the compositional ratio of these atoms in the corresponding layer. The ratio and characteristics of Cu/(In + Ga) and Ga/(In + Ga) were further modulated to attain higher efficiency in the devices. Furthermore, the width of the interfacial zone decreased at the Mo/CIGS interface because the diffusion depth of the Se atoms contracted from 1300 nm to 1200 nm. After RTA treatment, the absolute efficiency of the CIGS solar cells was enhanced by 1.2%. Our results suggest that RTA treatment reduces series resistance, optimizes the position of the minimum bandgap in the CIGS thin film, and improves the crystallinity of the CIGS thin film, which is responsible for the improvement in conversion efficiency.

We demonstrate that Mn doping in the layered sulfides Bi_4O_4S_3 leads to stable Bi_(4−x)Mn_x O_4S_3 compounds that exhibit both long-range ferromagnetism and enhanced superconductivity for 0.075 ≤ x ≤ 0.15, with a possible record superconducting transition temperature (T_c ) ∼15 K among all BiS_2-based superconductors. We conjecture that the coexistence of superconductivity and ferromagnetism may be attributed to Mn doping in the spacer Bi_2O_2 layers away from the superconducting BiS_2 layers, whereas the enhancement of T_c may be due to excess electron transfer to BiS_2 from the Mn^(4+)/Mn^(3+) substitutions in Bi_2O_2. This notion is empirically corroborated by the increased electron-carrier densities upon Mn doping, and by further studies of the Bi_(4−x)A_xO_4S_3 compounds (A = Co, Ni; x=0.1 , 0.125), where the T_c values remain comparable to that of the undoped Bi_4O_4S_3 system (∼4.5 K) due to lack of 4+ valences in either Co or Ni ions for excess electron transfer to the BiS_2 layers. These findings therefore shed new light on feasible pathways to enhance the T_c values of BiS_2-based superconductors, although complete elucidation of the interplay between superconductivity and ferromagnetism in these anisotropic layered compounds awaits the development of single crystalline materials for further investigation.

The crystal structures of Os2C were extensively investigated using the structure search method from the first-principles calculations. In contrast to the P6 3 /mmc phase previously proposed as the ground state at ambient pressure, an energetically favorable structure with space group P-6m2 was found more stable at ambient condition. The structural stabilities of the new phase are confirmed by the phonon dispersion and elastic constants. Further calculations indicate that the newly predicted P-6m2 phase is ultra-incompressible with a high bulk modulus of 387 GPa and has a larger ideal shear strength than the P6 3 /mmc phase.

Near-infrared photoluminescence (PL) of calcium boroaluminate (CABAL) glasses codoped with Er 2 O 3 and Tm 2 O 3 has been investigated by dual-wavelength pumping at 795 and 476 nm. Spectrum shape of broadband emission could be modulated by controlling the power ratio of two pumping lines (P 476 /P 795 ). The result shows that the full width at half maximum can reach ∼500 nm in the wavelength range from 1.3 to 2.0 μm by controlling P 476 /P 795 = 12. The PL spectra show four characteristic peaks located at 1.46, 1.53, 1.58 and 1.80 μm, corresponding to Tm 3+ : 3 H 4 → 3 F 4 , Er 3+ : 4 I 13/2 → 4 I 15/2 , Tm 3+ : 1 G 4 → 3 F 2 and Tm 3+ : 3 F 4 → 3 H 6 emissions, respectively. The energy transfer (ET) (ET1: Er 3+ : 4 I 13/2 , Tm 3+ : 3 F 4 → Er 3+ : 4 I 15/2 , Tm 3+ : 3 H 4 and ET2: Er 3+ : 4 I 13/2 , Tm 3+ : 3 H 6 → Er 3+ : 4 I 15/2 , Tm 3+ : 3 F 4 ) between Er 3+ and Tm 3+ ions play important roles in the luminescence mechanisms. In addition, a new ET process (ET: Tm 3+ : 1 G 4 , Er 3+ : 4 F 9/2 → Tm 3+ : 3 F 2 , Er 3+ : 4 F 7/2 ) was identified. The flat broadband emission with the bandwidth of ∼500 nm could be realized by changing P 476 /P 795 as a result of the radiative transitions, Tm–Tm cross-relaxation (Tm 3+ : 3 H 4 , 3 H 6 → Tm 3+ : 3 F 4 , 3 F 4 ) and Er–Tm ET processes.