Photoluminescence analysis of InGaP top cells for high-efficiency multi-junction solar cells

A way of evaluate the minority-carrier lifetime by using photoluminescence (PL) measurement is proposed which includes self-absorption. The room-temperature PL intensity is analyzed theoretically for bulk crystals and a device with n⁺-p junction configuration, based on a one-dimensional model. Photoluminescence analysis of In_0.5Ga_0.5P solar cells grown on GaAs and Si substrates by MOCVD (metal organic vapor deposition) have been carried out and compared with the properties of the In_0.5Ga_0.5P solar cells. By improving minority-carrier lifetime, high-efficiency In_0.5Ga_0.5P cells on GaAs substrates with an efficiency of 18.5% have been made.     

Effect of substrate crystal on mechanical stresses in heteroepitaxial photo-conversion Ga x In1 − x P/GaP structures

The occurrence of mechanical stresses in heteroepitaxial photo-conversion Ga _x In_{1 ? x} P structures (0.6 ≤ x ≤ 0.8) depending on their composition and the width of the substrate GaP monocrystal is studied. At given temperatures of layer growth and solid solution compositions, mechanical stresses in a heterostructure are shown to be appreciably weakened due to an increase in GaP substrate bending as the substrate thickness is decreased from 400 to 100 μm.     

Tunnel current through a miniband in InGaAs quantum dot superlattice solar cells

We report the tunnel current through a miniband in In_0.4Ga_0.6As quantum dot (QD) superlattice solar cells fabricated using molecular beam epitaxy. High-quality and well-aligned In_0.4Ga_0.6As QD superlattice structures with an interdot spacing of 3.5 nm were grown without using a strain balancing technique. 10-stack In_0.4Ga_0.6As QD superlattice solar cells had a high open circuit voltage and good cell characteristics even when the interdot spacing was reduced to 3.5 nm. Moreover, a short-circuit current density increases as the interdot spacing decreases. From the temperature dependence of the external quantum efficiency for QD solar cells with different interdot spacings, we observed the tunnel current through a miniband in QD superlattices with an interdot spacing of 3.5 nm.     

Triple-axis X-ray reciprocal space mapping of InyGa1−yAs thermophotovoltaic diodes grown on (1 0 0) InP substrates

Analysis of the composition, strain-relaxation, layer-tilt, and the crystalline quality of In_yGa_1−yAs/InP_1−xAs_x thermophotovoltaic (TPV) diodes grown by metal-organic vapor phase epitaxy (MOVPE) is demonstrated using triple-axis X-ray reciprocal space mapping techniques. In_0.53Ga_0.47As (E_gap=0.74 eV) n/p junction diodes are grown lattice matched (LM) to InP substrates and lattice-mismatched (LMM) In_0.67Ga_0.33As (E_gap=0.6 eV) TPV diodes are grown on three-step InP_1−xAs_x (0<x<0.32) buffer layers on InP substrates. X-ray reciprocal space maps about the symmetric (4 0 0) and asymmetric (5 3 3) reciprocal lattice points (RELPs) determine the in-plane and out-of-plane lattice parameters and strain of the In_yGa_1−yAs TPV active layer and underlying InP_1−xAs_x buffers. Triple-axis X-ray rocking curves about the LMM In_0.67Ga_0.33As RELP show an order of magnitude increase of its full-width at half-maximum (FWHM) compared to that from the LM In_0.53Ga_0.47As (250 vs. 30 arcsec). Despite the significant RELP broadening, the photovoltaic figure of merits show that the electronic quality of the LMM In_0.67Ga_0.33As approaches that of the LM diode material. This indicates that misfit-related crystalline imperfections are not dominating the photovoltaic response of the optimized LMM In_0.67Ga_0.33As material compared with the intrinsic recombination processes and/or recombination through native point defects, which would be present in both LMM and LM diode material. However, additional RELP broadening in non-optimized LMM In_0.67Ga_0.33As n/p junction diodes does correspond to significant degradation of TPV diode open-circuit voltage and minority carrier lifetime demonstrating that there is correlation between X-ray FWHM and the electronic performance of the LMM TPV diodes.     

Determination of Cu(In1−xGax)3Se5 defect phase in MBE grown Cu(In1−xGax)Se2 thin film by Rietveld analysis

Quantitative phase analysis of Cu(In_1−xGa_x)Se₂ (CIGS) thin film grown over Mo coated soda lime glass substrates was studied by Rietveld refinement process using room temperature X-ray data at θ-2θ mode. Films were found to contain both stoichiometric Cu(In_1−xGa_x)Se₂ and defect related Cu(In_1−xGa_x)₃Se₅ phases. Best fitting was obtained using crystal structure with space group I-42d for Cu(In_1−xGa_x)Se₂ and I-42m for Cu(In_1−xGa_x)₃Se₅ phase. The effects of Ga/III (=Ga/In+Ga=x) ratio and Se flux during growth over the formation of Cu(In_1−xGa_x)₃Se₅ defect phase in CIGS was studied and the correlation between quantity of Cu(In_1−xGa_x)₃Se₅ phase and solar cell performance is discussed.     

The influence of concentrated solar radiation on the properties of Ga<Subscript>0.7</Subscript>In<Subscript>0.3</Subscript>P/GaP photoconverters

The properties of Ga_0.7In_0.3P/GaP heterophotoconverters with a two-sided contact grid are studied in the range of solar radiation concentration K _s = 1−100 times and with natural convective heat exchange. It is found that, in the considered photoconverters, the dependences of an idle running voltage, the duty cycle of the current-voltage characteristic, and the efficiency on concentration are additionally improved due to high heat conduction of GaP and the temperature stability of the broad-band heterophotoconverter with “transparent“ structural design.     

Comparison of point defects in CuInSe2 and CuGaSe2 single crystals

Hall-effect and photoluminescence measurements have been carried out on as-grown and In/Ga-annealed CuInSe₂ and CuGaSe₂ single crystals grown by chemical vapor transport. Various defect levels in these related compounds have been identified and compared. V_Cu and V_Se show similar properties and activation energies in both materials. A tremendous difference is observed in the behavior of III_Cu antisite defects. Ga_Cu levels in CuGaSe₂ are much deeper than In_Cu in CuInSe₂, and furthermore, the formation of In_Cu is much easier compared to Ga_Cu. This is related to the higher formation energy of Ga_Cu in CuGaSe₂. Due to this difference in the defect chemistry of both compounds, it has not been possible until now, to prepare n-type CuGaSe₂ crystals, whereas CuInSe₂ is easily transformed from p- to n-type by annealing in vacuum or In-atmosphere.     

AlxGa1−x)0.65In0.35As monolithic multijunction solar cells

A simple graphical method is used to establish that the (Al_xGa_1−x)_0.65In_0.35As semiconductor alloy provides the range of energy-band gaps required to both maximize power conversion efficiency and achieve current-matching for two-terminal, multijunction solar cells. Within this framework, the development needs of a three junction, monolithic solar cell with lattice-matched subcells and a strain-relieved Ga_yIn_1−yAs/GaAs pseudo-substrate are discussed. The theoretical limiting efficiency of the proposed design is approximately 47.2% at 1 sun (AM 1.5 spectrum).     

Performance of solid oxide fuel cells based on proton-conducting BaCe0.7In0.3-xYxO3-δ electrolyte

The performances of solid oxide fuel cells with proton conductors BaCe_0.7In_0.3−xY_xO_3−δ (BCIY, x = 0, 0.1, 0.2, 0.3) as electrolytes were investigated in this work. The cell based on BaCe_0.7In_0.2Y_0.1O_3−δ electrolyte showed maximum power outputs of 0.114, 0.204 and 0.269 Wcm⁻² at 600, 650 and 700 °C, respectively. After operating at a constant cell voltage output of 0.5V for 40h, no obvious degradation in performance was observed for the cells based on BaCe_0.7In_0.3O_3−δ and BaCe_0.7In_0.2Y_0.1O_3−δ electrolytes. However, although relatively lower resistances and higher initial power outputs were found for cells based on BaCe_0.7In_0.1Y_0.2O_3−δ and BaCe_0.7Y_0.3O_3−δ electrolytes, rapid cell performance degradations were observed for these two cells. The stability under cell operating conditions remained a challenge for cells using BaCe_0.7In_0.1Y_0.2O_3−δ and BaCe_0.7Y_0.3O_3−δ electrolytes.     

Improved efficiency of Al0.36Ga0.64As solar cells with a ppnn structure

Improvement of efficiency of Al_0.36Ga_0.64As solar cells is advanced in two aspects of minority-carrier lifetime: reduction of majority-carrier concentration in the emitter and base layers, and reduction of deep levels in the back-surface-field (BSF) layer. A pp⁻n⁻n structure is proposed to optimize the use of the effect of reduced majority-carrier concentration, and its effectiveness verified in a preparatory experiment on Al_0.3Ga_0.7As solar cells. A very poor photoluminescence (PL) decay time (below 0.3 ns) of a BSF layer heavily doped with Si becomes 14-fold longer when Se is applied to the dopant instead of Si, resulting in an improvement of the external quantum efficiency near the absorption edge. These two aspects of this study lead to the realization of 16.6% efficiency under 1-sun, AM 1.5 global conditions with an Al_0.36Ga_0.64As solar cell.     

Synthesis of Zn(InxGa1-x)2O4 solid-solutions with tunable band-gaps for enhanced photocatalytic hydrogen evolution under solar-light irradiation

The systematic investigation of In³⁺ ions doped ZnGa₂O₄ applying to photocatalytic H₂ evolution (PHE) under simulated solar-light irradiation was first reported here. A series of Zn(In_xGa_1-x)₂O₄ (x = 0 to 0.4) solid-solutions were obtained by sol-gel method and characterized by XRD, SEM, elemental mapping, XPS, UV–Vis DRS and N₂ adsorption measures. The concentration of In³⁺ ions remarkably enhanced the light-harvesting capability of Zn(In_xGa_1-x)₂O₄ solid-solutions in the visible-light region, and successfully regulated the positions of the CB-bottom potential, ultimately improving the photocatalytic capabilities under simulated solar-light irradiation. Among composites containing different In³⁺ ions dosages, Zn(In_0.1Ga_0.9)₂O₄ demonstrated the most excellent photocatalytic capability for solar-light-driven PHE reaction (H₂: 240.6 μmol/h/g), in which the stability of the Zn(In_0.1Ga_0.9)₂O₄ was confirmed by several techniques.     

Enhanced reversible hydrogen storage properties of a Mg–In–Y ternary solid solution

A Mg(In, Y) ternary solid solution was successfully synthesized by two-step method, namely sintering the elemental powders and subsequent milling. The formation of Mg(In, Y) indicates that the solubility of Y in the Mg lattice is expanded due to the existence of In. The as-synthesized Mg₉₀In₅Y₅ solid solution transformed to MgH₂, YH₃, In₃Y and MgIn compound upon hydrogenation, the hydrogenated products except for the YH₃ recovered to Mg(In, Y) solid solution after dehydrogenation. The Mg₉₀In₅Y₅ solid solution exhibited a decreased reaction enthalpy of 62.9 kJ/(mol H₂), reduction by ca. 5 kJ/(mol H₂) or 12 kJ/(mol H₂) than the Mg₉₅In₅ binary solid solution and pure Mg, respectively. The working temperature as well as the activation energies for the hydriding and dehydriding were also decreased in comparison with those of Mg(In) binary solid solution, which are attributed to the reduced reaction enthalpy and the catalytic role of YH₃. Our work indicates that the thermodynamic and kinetic tuning of MgH₂ are realized in the Mg(In, Y) ternary solid solution.     

High-efficiency InGaP/In0.01Ga0.99As tandem solar cells lattice-matched to Ge substrates

Conversion efficiency (AM1.5G) of more than 30% was achieved by adding a small quantity of Indium into a GaAs bottom cell in the conventional tandem solar cell on Ge substrate. It was found that the lattice-mismatch between GaAs and Ge caused misfit-dislocations in thick GaAs layers and reduced an open-circuit voltage (V_oc) of the cell. An In_0.49Ga_0.51P/In_0.01Ga_0.99As tandem cell lattice-matched to Ge showed a great improvement in efficiency, which was attributed to an increase in the V_oc of the bottom cell and increases in the photocurrents both in the top and bottom cells due to reductions in band-gap energy.     

Hydrogen sensing characteristics of AlGaInP/InGaAs enhancement/depletion-mode co-integrated doping-channel field-effect transistors

In this article, the hydrogen sensing characteristics of Al_0.25Ga_0.25In_0.5P/In_0.1Ga_0.9As enhancement/depletion-mode co-integrated pseudomorphic doping-channel field-effect transistors by wet selectively etching process are demonstrated. At drain current of 0.1 mA/mm, the threshold voltages are of −0.97 (+0.6) V and −1.22 (+0.31) V in air and at hydrogen concentration of 9800 ppm, respectively, for the depletion (enhancement)-mode device. In addition, by employing the co-integrated FETs the transfer characteristics of the direct-coupled FET logic (DCFL) obviously vary under hydrogen ambience. The V_OH value reduces and the V_OL value increases in the DCFL with the measurement of hydrogen detection.     

Janus Ga2SeTe and In2SeTe nanosheets: Excellent photocatalysts for hydrogen production under neutral pH

In the past few years, Janus nanosheets have attracted much interest according to their specific structure and considerable potential to address the energy and environmental issues. Herein, the electronic, optical and photocatalytic properties of two-dimensional Janus Ga₂SeTe and In₂SeTe have been studied using ab-initio computations based on the density functional theory. The obtained results show that these nanomaterials exhibit a semiconductor behavior with direct and moderate bandgaps using hybrid HSE06 functional. Subsequently, the understudied compounds present suitable optical conductivity, absorption, transmission and reflectivity for water splitting under the ultraviolet–visible light irradiation. Interestingly, the band edge positions of Janus Ga₂SeTe and In₂SeTe excellently straddle the redox potentials of water under neutral pH. Additionally, the free energy values for the formation of H₂ from H adsorbed on the Ga₂SeTe and In₂SeTe compounds are respectively 1.304eV and 0.976eV at pH = 7. More excitingly, the present study proposes strain engineering approach to improve the photocatalytic performance of the Janus Ga₂SeTe and In₂SeTe monolayers. Specifically, the investigated semiconductors show more appropriate band edge alignment and better hydrogen evolution reaction activity under biaxial tensile strain, which fulfil the water splitting requirements at neutral pH conditions. Our findings conclude that the Janus Ga₂SeTe and In₂SeTe nanosheets are promising candidates for photocatalytic hydrogen production.     

Fabrication of nano N-doped In2Ga2ZnO7 for photocatalytic hydrogen production under visible light

N-doped In₂Ga₂ZnO₇ photocatalysts were fabricated by solid state reaction route. All the prepared photocatalysts were successfully characterised by PXRD, optical absorption spectra, SEM, TEM, XPS, BET surface area and photoresponse studies. The formation of In₂Ga₂ZnO₇ was confirmed by the PXRD pattern. Optical absorption spectra showed that the visible light absorption of all the photocatalysts were enhanced by nitrogen doping. Among all the prepared photocatalysts, 1 wt% Pt loaded N-GaInZn-500 showed enhanced photocatalytic activity towards hydrogen evolution under visible light irradiation in presence of 10 vol% methanol solution as sacrificial agent. The excellent photocatalytic activity of N-GaInZn-500 is in agreement with N-content, bandgap energy, PL intensity and Surface area.     

The effects of the morphology on the CIGS thin films prepared by CuInGa single precursor

Cu(In_xGa_1−x)Se₂ (CIGS) thin films were prepared by selenization of CuInGa single-layer metallic precursors. At the first stage, CuInGa metallic precursors were deposited onto soda lime glass by direct current (DC) magnetron sputtering system using a CuInGa ternary alloy target with a composition ratio of Cu:In:Ga of 1:0.7:0.3. The precursor films were reacted with Se vapor in vacuum evaporation system. By means of X-ray diffraction (XRD), field emission scanning electron microscope (SEM) and electron probe microanalysis (EPMA), it was found that CIGS thin films exhibit large facetted grains and single chalcopyrite phase with preferred orientation along (1 1 2) plane. Meanwhile, the surface roughness of the CIGS films can be determined by the morphology of the precursor films.     

Methods to improve output voltage and specific photoconverter electrical capacity

Cascade photoconverters based on the Al_0.43In_0.57P/InP/Ga_0.47In_0.53As/InP/Al_0.43In_0.57P system are studied. It is shown that with progressive switching of all the component elements, the short-circuit current density of the cascade is I _{sh. cir.} ≈10 mA/cm² and the output voltage of the system will be the sum of the voltages of all the component structures, which achieves V _ol ≈13–14 V.     

Al0.3Ga0.7As/GaAs concentrator solar cells

An Al_0.3Ga_0.7As/GaAs tandem solar cell was fabricated in a commercial reactor which has been specially modified for dual operation of both atomic layer epitaxy (ALE) and metalorganic chemical vapor deposition (MOCVD) growth modes. The p-type and n-type dopants were carbon and silicon, respectively, and the required doping concentrations were achieved by optimizing growth conditions such as V/III ratio (mole ratio of group V atoms to group III atoms), exposure times to reactant gases, and growth temperatures. The current-voltage (I–V) characteristics indicate that, up to 53 Suns, the tunnel junction does not seem to result in any appreciable deterioration in the multijunction solar cell's performance. The measured efficiency increases with increasing solar concentration up to a point where a region of negative resistance starts to appear in the I–V characteristics.     

Reversible de-/hydriding characteristics of a novel Mg18In1Ni3 alloy

The present work demonstrates the reversible hydrogen storage properties of the ternary alloy Mg₁₈In₁Ni₃, which is prepared by ball-milling Mg(In) solid solution with Ni powder. The two-step dehydriding mechanism of hydrogenated Mg₁₈In₁Ni₃ is revealed, namely the decomposition of MgH₂ is involved with different intermetallic compounds or Ni, which leads to the formation of Mg₂Ni(In) solid solution or unknown ternary Mg–In–Ni alloy phase. As a result, the alloy Mg₁₈In₁Ni₃ shows improved thermodynamics in comparison with pure Mg. The Ni addition also results in the kinetic improvement, and the minimum desorption temperature is reduced down to 503 K, which is a great decrease comparing with that for Mg–In binary alloy. The composition and microstructure of Mg–In–Ni ternary alloy could be further optimized for better hydrogen storage properties.