Nondestructive interface construction for CdS-buffered ZnO nanorod/Cu<Subscript>2</Subscript>O composite structure solar cells

In this work, ZnO nanorod/Cu₂O composite nanostructure solar cells were prepared using hydrothermal growth and electrodeposition. The CdS layer was added between ZnO and Cu₂O to suppress carrier reverse recombination. Nondestructive interface deposition methods were employed to prepare CdS and Cu₂O functional layers. The CdS layers were unconventionally deposited in non-alkaline solution, which can inhibit etching on the ZnO surface, and Cu₂O layers were electrodeposited in ZnO-buffered alkaline solution which can also inhibit etching on the ZnO surface. Finally, the performance of solar cells was improved by adding a highly resistive CdS intermediate layer between ZnO and Cu₂O layers. This work demonstrated the nondestructive interface approach of chemical solution deposition of functional layers on ZnO and possibilities for further improvements to the performance of Cu₂O-based nanostructure solar cells with the addition of an intermediated layer.     

Photovoltaic performance of flexible Cu(In,Ga)Se2 thin-film solar cells with varying Cr impurity barrier thickness

We report the effect of Cr impurity barrier on Cu(In,Ga)Se₂ (CIGS) thin-film solar cells prepared on flexible substrates. The Cr films with varying the thickness (t_Cr) were deposited on stainless steel substrates using direct-current magnetron sputtering. The solar cell performance was improved by increasing t_Cr since the diffusion of Fe impurities from the substrate to CIGS was suppressed. Although the elemental composition, grain size, and strain of CIGS film showed little change with varying Fe content, the fill factor and the short-circuit current density increased as decreasing Fe. The Fe increased the series resistance, shunt paths, and saturation current density. The reduction of Fe caused a steeper bandgap grading in CIGS which enhances current collection due to higher electric fields in bulk CIGS. CIGS solar cells with 1000 nm-thick Cr barrier showed the best conversion efficiency of 9.05%.     

An investigation into ultra-thin pseudobinary oxide (TiO<Subscript>2</Subscript>)<Subscript>x</Subscript>(Al<Subscript>2</Subscript>O<Subscript>3</Subscript>)<Subscript>1-x</Subscript> films as high-<Emphasis Type="Italic">k</Emphasis> gate dielectrics

As potential gate dielectric materials, pseudobinary oxide (TiO₂)_x(Al₂O₃)_1-x (0.1≤x≤0.6) films (TAO) were deposited on Si (100) substrates by pulsed-laser deposition method and studied systematically via various measurements. By a special deposition process, including two separate steps, the TAO films were deposited in the form of two layers. The first layer was deposited at room temperature and the second layer was completed at the substrate temperature of 400 °C. Detailed data show that the properties of the TAO films are closely related to the ratio between TiO₂ and Al₂O₃. The existence of the first layer deposited at room temperature can effectively restrain the formation of the interfacial layer. And according to the results of X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy performed on the films, no other information belonging to the silicon oxide could be observed. For the (TiO₂)_0.4(Al₂O₃)_0.6 film, the best result has been achieved among all samples and its dielectric constant is evaluated to be about 38. It is valuable for the amorphous TAO film as one of the promising dielectric materials for high-k gate dielectric applications. PACS 77.55.+f; 73.40.Qv; 81.15.Fg     

Inkjet printed Cu(In,Ga)S<Subscript>2</Subscript> nanoparticles for low-cost solar cells

Cu(In,Ga)Se₂ (CIGSe) thin film solar cells were fabricated by direct inkjet printing of Cu(In,Ga)S₂ (CIGS) nanoparticles followed by rapid thermal annealing under selenium vapor. Inkjet printing is a low-cost, low-waste, and flexible patterning method which can be used for deposition of solution-based or nanoparticle-based CIGS films with high throughput. XRD and Raman spectra indicate that no secondary phase is formed in the as-deposited CIGS film since quaternary chalcopyrite nanoparticles are used as the base solution for printing. Besides, CIGSe films with various Cu/(In + Ga) ratios could be obtained by finely tuning the composition of CIGS nanoparticles contained in the ink, which was found to strongly influence the devices performance and film morphology. To date, this is the first successful fabrication of a solar device by inkjet printing of CIGS nanoparticles.     

Dielectric properties of thin ferroelectric Sn<Subscript>2</Subscript>P<Subscript>2</Subscript>S<Subscript>6</Subscript> films deposited by thermal evaporation

The structure, microstructure, and temperature and field dependences of the dielectric properties of thin (0.5–8.0μm) Sn₂P₂S₆ ferroelectric films deposited onto glass and aluminum foil substrates by thermal vacuum evaporation in a quasi-closed volume are studied. The film-thickness and frequency dependences of the dielectric properties and the unipolarity of the C–V characteristics are explained by the presence of near-surface Schottky-type barrier layers.     

Effect of PVA addition on formation of spray-deposited Sm<Subscript>0.5</Subscript>Sr<Subscript>0.5</Subscript>CoO<Subscript>3</Subscript> thin films on CeO<Subscript>2</Subscript> substrates

Nano-crystalline films of Sm_0.5Sr_0.5CoO₃ (SSC) have been formed on CeO₂ substrates by spraying stoichiometric aqueous solution containing Sm, Sr, and Co ions. Effect of polyvinyl alcohol (PVA) addition as a complexing agent in spray solution on stoichiometry, crystallite size, morphology, and transport properties of film are studied. The results showed that the SSC cathode had maximum crystallite size for 40% PVA addition. Electrical performance of film decreases with decrease in the particle size, while the electronic to ionic predominance transition temperature decreases with decreasing particle size. These films are studied for their potential application as a cathodic material in developing intermediate temperature solid oxide fuel cells.     

Effects of Gd<Superscript>3+</Superscript> modifications on the photoelectrochemical properties of TiO<Subscript>2</Subscript>-based dye-sensitized solar cells

In this paper, TiO₂ particles (~30 nm) modified with Gd₂O₃-coating layer (~2 nm) for dye-sensitized solar cells (DSSCs) were fabricated via the hydrothermal method. Among the solar cells based on the Gd³⁺-doped TiO₂ photoanodes, the optimal conversion efficiency was obtained from the 0.025Gd³⁺-modified TiO₂-based cell, with a 17.7% improvement in the efficiency as compared to the unmodified one (7.18%). This enhancement was probably due to the improved UV radiation harvesting via a down-conversion luminescence process by Gd³⁺ ions, enhancement of visible light absorption and improved dye loading capacity. In addition, after Gd modification, a thin coating could be formed on the TiO₂ nanoparticles, which worked as an energy barrier and resulted in a lower charge recombination.     

A new green synthesis method of CuInS<Subscript>2</Subscript> and CuInSe<Subscript>2</Subscript> nanoparticles and their integration into thin films

A new preparation method for CuInS₂ and CuInSe₂ nanoparticles synthesis is described without using any organic solvent. Heating Cu, In, and S/Se precursors dissolved in water for 30 min in a microwave oven in the presence of mercapto-acetic acid leads to monodispersed chalcopyrite nanoparticles. No precipitation of these nanoparticles is observed after several months at room temperature. These new materials have been thoroughly characterized to confirm their compositions, sizes, and structure without any filtration. Transmission electron microscopy (TEM) confirmed particle sizes below 5 nm. Energy dispersive X-ray analysis (EDXA) confirmed the chemical composition of these samples. X-ray diffraction (XRD) showed a chalcopyrite-type structure with crystallite size of about 2 nm. No difference has been observed between batch and continuous synthesis processes. Cu _x InS₂ and Cu _x InSe₂ nanoparticles, with x < 1, have been also synthesized and identified. Simulation using a commercial software confirmed the difference between copper poor (Cu _x InS₂) and copper rich (CuInS₂) chalcopyrite structures. Conventional spray deposition techniques have been used to form relatively thin films on solid substrates.     

A comparative study on the morphology of P3HT:PCBM solar cells with the addition of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles by spin and rod coating methods

Our previous study presented up to 20% power conversion efficiency (PCE) enhancement of poly(3-hexylthiophene):phenyl-C₆₁-butyric acid methyl ester (P3HT:PCBM) solar cells under the Fe₃O₄ nanoparticles (NPs) self-assembly (SA) effect by spin coating. Fe₃O₄ NPs (about 11 nm hydrodynamic diameter) form a thin layer at the top interface of the light absorbing active layer, which results in the generation of PCBM rich region improving the charge transport (Zhang et al. Sol Energ Mat Sol C 160:126–133, 2017). In order to investigate the feasibility of this Fe₃O₄ NPs SA effect under large-scale production condition, a smooth rod was implemented to mimic roll-to-roll coating technique and yield active layers having about the same thickness as the spin-coated ones. Small angle neutron scattering and grazing incidence X-ray diffraction were employed finding out similar morphologies of the active layers by these two coating techniques. However, rod-coated solar cell’s PCE decreases with the addition of Fe₃O₄ NPs compared with the one without them. This is because PCBM rich region is not created at the top interface of the active layer due to the absence of Fe₃O₄ NPs, which is attributed to the weak convective flow and low diffusion rate. Moreover, in the rod-coated solar cells, the presence of Fe₃O₄ NPs causes decrease in P3HT crystallinity, thus the charge transport and the device performance. Our study confirms the role of spin coating in the Fe₃O₄ NPs SA effect and enables researchers to explore this finding in other polymer nanocomposite systems.     

Fabrication and characterization of CdS-sensitized TiO<Subscript>2</Subscript> nanotube photoelectrode

CdS quantum dot (Qd)-sensitized TiO₂ nanotube array photoelectrode is synthesised via a two-step method on tin-doped In₂O₃-coated (ITO) glass substrate. TiO₂ nanotube arrays are prepared in the ethylene glycol electrolyte solution by anodizing titanium films which are deposited on ITO glass substrate by radio frequency sputtering. Then, the CdS Qds are deposited on the nanotubes by successive ionic layer adsorption and reaction technique. The resulting nanotube arrays are characterized by scanning electron microscopy, X-ray diffraction (XRD) and UV–visible absorption spectroscopy. The length of the obtained nanotubes reaches 1.60 μm and their inner diameter and wall thickness are around 90 and 20 nm, respectively. The XRD results show that the as-prepared TiO₂ nanotubes array is amorphous, which are converted to anatase TiO₂ after annealed at 450 °C for 2 h. The CdS Qds deposited on the TiO₂ nanotubes shift the absorption edge of TiO₂ from 388 to 494 nm. The results show that the CdS-sensitized TiO₂ nanotubes array film can be used as the photoelectrode for solar cells.     

Electro-optic properties of epitaxial Sr<Subscript>0.6</Subscript>Ba<Subscript>0.4</Subscript>Nb<Subscript>2</Subscript>O<Subscript>6</Subscript> films grown on MgO substrates using Li<Subscript>x</Subscript>Ni<Subscript>2-x</Subscript>O buffer layer

Textured Li_xNi_2-xO (LNO) thin films have been fabricated on (001)MgO substrates by pulsed laser deposition technique. The as-deposited LNO films shows a conductivity of 2.5×10^-3 Ω m and possess a transmittance of about 35% in the visible region. Subsequent deposition of Sr_0.6Ba_0.4Nb₂O₆ (SBN60) thin film on these LNO-coated MgO substrates resulted in a textured SBN layer with a 〈001〉 orientation perpendicular to the substrate plane. Phi scans on the (221) plane of the SBN layer indicated that the films have two in-plane orientations with respect to the substrate. The SBN unit cells were rotated in the plane of the film by ± 8.2° as well as ± 45° with respect to the LNO/MgO substrate. Besides the highly (00l)-orientation, the SBN films also exhibited a dense microstructure as shown by scanning electron microscopy. The electro-optic coefficient (r₃₃) of the SBN film was measured to be 186 pm/V. On the basis of our results, we have demonstrated that the LNO film can be used as a buffer layer as well as a transparent bottom electrode for waveguide applications. The SBN/LNO heterostructure is also a suitable candidate for integrated electro-optics devices. PACS  42.79.Gn; 42.82.Et; 78.20.Ci     

Electronic processes at the interfaces between photoactive layers and TiO<Subscript> <Emphasis Type="Italic">x</Emphasis> </Subscript> buffer layers in organic solar cells

The effect a layer of TiO_x located between a photoactive layer and a metallic Al electrode has on the photovoltaic properties of an organic solar cell based on P3HT:PC₇₀BM polymer is studied. The optimum thickness of the TiO_x layer at which the efficiency of the solar cells is highest and the TiO_x layer ensures the transfer of electrons from the photoactive polymer layer to the electrode while blocking vacancies is found to be 10 nm. The effect oxygen has on electronic processes during the operation of the photovoltaic cell is discussed.     

Effect of mechanical deformation on the critical current in YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7−<Emphasis Type="Italic">b</Emphasis></Subscript> superconducting films

It is shown that local mechanical bending of YBa₂Cu₃O_7−b Ag-coated superconducting films deposited on flexible metal substrates in the temperature interval 77–300 K may increase the critical density J _c of the transport current to values as high as 10⁶ A/cm² or even higher at 77 K. Also, bending decreases the voltage criterion. This means a rise in the intergranular conductivity and, accordingly, a reduction of Joule losses.     

A high efficient antireflective down-conversion Y<Subscript>2</Subscript>O<Subscript>3</Subscript>:Bi<Superscript>3+</Superscript>, Yb<Superscript>3+</Superscript> thin films

The high efficient antireflective down-conversion Y₂O₃:Bi, Yb films have been prepared successfully on Si(100) substrates by pulsed laser deposition (PLD) method, Upon excitation of ultraviolet photon varying from 300 to 400 nm, near-infrared emission of Yb³⁺ was observed for the film, can be efficiently absorbed by silicon (Si) solar cell. Most interestingly, there is a very low average reflectivity 1.46% for the incident light from 300 to 1100 nm. To the best of our knowledge, this is the lowest reflectance for the down-conversion thin films prepared by cost efficient method. The surface topography of the high efficient antireflective films can be controllably tuned through the substrate template regulation by optimizing process parameters. Besides, the results showed that there is a close relationship between luminescent property and morphology of the film. With the change of the surface morphology, the intensity of Bi³⁺ and Yb³⁺ emission peaks increase first and then decrease. The obtained results demonstrate that this film can enhance the Si solar cell efficiency through light trapping and spectrum shifting.     

Structure and orientation of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> fibers used in YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript> <Emphasis Type="Italic">y</Emphasis> </Subscript> sputtering

The internal structure and orientation of thin (150–300 μm) flexible Al₂O₃ fibers used as substrates for third-generation high-temperature superconducting wires are studied by different methods. It is shown that using scanning electron microscopy, electron backscatter diffraction, transmission electron microscopy, and X-ray diffraction, one can reliably determine the position of the \((1\bar 102)\) plane, on which good YBa₂Cu₃O_y films can be grown.     

Application of multi-buffer layer of (Zn,Mg)O/CdS in Cu2ZnSn(S,Se)4 solar cells

(Zn,Mg)O (ZMO) buffer layer has attracted attention for having the potential to control the conduction band offset of buffer layer and large band-gap (Eg) Cu₂ZnSn(S,Se)₄ (CZTSSe) absorber interface, where the ZMO layer is deposited by the sputtering. However, the solar cell efficiency is decreased with the ZMO layer as compared with the CdS layer. The decrease in conversion efficiency is attributed to the sputtering damage on the absorber and high light reflection from the surfaces of CZTSSe solar cells. To completely suppress the damage, a CdS layer with very thin thickness of 20 nm is inserted between the ZMO layer and the CZTSSe layer. In addition, MgF₂ layers are deposited on CZTSSe solar cells as anti-reflection coating. Ultimately, the solar cell with multi-buffer layer of ZMO/thin-CdS is almost same level as that with the CdS layer. Therefore, the multi-buffer layer can be an appropriate buffer layer of the large-Eg CZTSSe layer.     

Magnetic properties of BiFe<Subscript>0.93</Subscript>Mn<Subscript>0.07</Subscript>O<Subscript>3</Subscript> powders obtained by ultrasonic spray pyrolysis

Samples of BiFe_0.93Mn_0.07O₃ with different specific surface area were synthesized for the first time by ultrasonic spray pyrolysis. The resulting powders consist of porous particles of a spherical shape of medium size ~0.5 μm and have record values of residual magnetization and coercive force. It is found that the magnetic properties of the porous powder particles are determined by the distortion of the crystal lattice and the presence of uncompensated magnetic moments of iron ions on the surface.     

A lithium salt additive Li<Subscript>2</Subscript>ZrF<Subscript>6</Subscript> for enhancing the electrochemical performance of high-voltage LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> cathode

In this work, Li₂ZrF₆, a lithium salt additive, is reported to improve the interface stability of LiNi_0.5Mn_1.5O₄ (LNMO)/electrolyte interface under high voltage (4.9 V vs Li/Li⁺). Li₂ZrF₆ is an effective additive to serve as an in situ surface coating material for high-voltage LNMO half cells. A protective SEI layer is formed on the electrode surface due to the involvement of Li₂ZrF₆ during the formation of SEI layer. Charge/discharge tests show that 0.15 mol L^?1 Li₂ZrF₆ is the optimal concentration for the LiNi_0.5Mn_1.5O₄ electrode and it can improve the cycling performance and rate property of LNMO/Li half cells. The results obtained by electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) demonstrate that Li₂ZrF₆ can facilitate the formation of a thin, uniform, and stable solid electrolyte interface (SEI) layer. This layer inhibits the oxidation decomposition of the electrolyte and suppresses the dissolution of the cathode materials, resulting in improved electrochemical performances.     

Synchrotron X-ray diffraction study of SrRuO<Subscript>3</Subscript>/SrTiO<Subscript>3</Subscript>/SrRuO<Subscript>3</Subscript> nano-sized heterostructures grown by laser MBE

Structural investigation using X-ray synchrotron radiation has been performed on SrRuO₃/SrTiO₃/SrRuO₃ epitaxial heterostructures, with each constituent layer a few unit cell thick grown on (001) SrTiO₃ substrate. Detailed information on the evolution of the in-plane lattice structure has been obtained, in these heterostructures, by grazing incidence diffraction measurements. The samples have been grown by low-pressure pulsed laser deposition. Under our deposition conditions, SrRuO₃ layers grow with an elongated cell perpendicular to the substrate surface. The in-plane pseudocubic lattice parameters do not match the in-plane square SrTiO₃ structure even in the case of very thin SrRuO₃ layers. Such a distortion was found to decrease with increasing the thickness of the SrTiO₃ barrier layer.     

Fast electrochromic response of porous-structured cobalt oxide (Co<Subscript>3</Subscript>O<Subscript>4</Subscript>) thin films by novel nebulizer spray pyrolysis technique

Electrochromic effect of cobalt oxide thin films was studied as a function of substrate temperature (573–673 K). Tricobalt tetraoxide (Co₃O₄) thin films were deposited on glass and fluorine-doped tin oxide (FTO) substrates by nebulized spray technique using cobalt nitrate as precursor material. The XRD patterns indicated (311) plane was dominant for all the films irrespective of the deposition temperature. Williamson-Hall (W-H) analysis was made to understand the strain variation in the prepared Co₃O₄ films under different deposition temperature by employing uniform deformation model (UDM). Scanning electron microscopy images revealed porous morphology for the film prepared at 623 K. The optical parameters such as refractive index (n), extinction coefficient (k), and band gap were derived from UV-visible spectra of Co₃O₄ films. The electrochromic performance of the deposited Co₃O₄ films was analyzed through cyclic voltammetry, chronocoulometry, chronoamperometry, and iono-optical studies.