Compound Semiconductor Solar Cells Research Articles

Formation and characterization of ZnS and CdZnS films using open-air chemical vapor deposition for buffer layers of compound semiconductor solar cells

ZnS and CdZnS (a mixed crystal phase of ZnS and CdS) were formed using the open-air CVD method. Cadmium diethyldithiocarbamate (C10H20CdN2S4) and zinc diethyldithiocarbamate (C10H20ZnN2S4) were used as the source materials for CdS and ZnS, respectively. By changing the ratio of source materials, it was found that the bandgap and the lattice constant of the CdZnS film were continuously changing without a miscibility gap. Furthermore, the bandgap of the obtained ZnS films was less than the reported bandgap of ZnS (3.68 eV) due to incorporation of oxygen. X-ray diffraction analysis revealed that the increase of Zn in CdZnS film generated a crystalline disorder. When the substrate temperature was changed from 421 °C to 464 °C, the deposition rate increased fourfold for the CdS and ZnS films. The impact of substrate temperature on the bandgap and lattice constant was found to be less pronounced.

One-step synthesis of CuInS2 nanoparticles using aqueous chelated metal complexes as a starting material

Thin film compound semiconductor solar cells, including copper indium sulfide (CIS), have potential as next-generation power supply sources. However, recent fabrication processes include gas phase reactions, which consume much energy and generate abundant loss of material resources. Therefore, the development of alternative eco-friendly methods without a gas phase reaction has been actively researched. Herein, we synthesize CIS nanoparticles via a liquid phase reaction using iminodiacetic acid (IDA) and glycine (Gly) as the complex reagent to homogenize copper and indium complexes. The X-ray diffraction (XRD) profiles of the as-synthesized nanoparticles in a buffer solution exhibit broad peaks, which nearly correspond to CIS. These peaks grow sharply after annealing. Selected area electron diffraction and high-resolution transmission electron microscopies indicate the presence of the (112) phase of CIS but the crystallinity of our CIS with IDA and Gly differs. The results indicate that maintaining a homogenized condition of metal complexes by pH stabilization using a buffer solution might be maybe important for aqueous synthesis of CIS.

Interdigitated back‐contact double‐heterojunction GaInP/GaAs solar cells

ABSTRACTInterdigitated back‐contact (IBC) silicon solar cells are coming of age, but the potential of IBC configurations for compound semiconductor solar cells is yet to be explored. We outline an approach to generalize the diffusion‐driven charge transport (DDCT) method, previously studied for IBC light‐emitting diodes, to develop DDCT solar cells, enabling an IBC double‐heterojunction structure. In particular, we simulate and compare the electrical performance of a GaInP/GaAs DDCT solar cell with an ideal one‐dimensional reference cell to establish how the lateral dimensions of the DDCT structures affect their operation. Also, the suitability of the DDCT solar cells for concentration photovoltaics is explored. The results show that the DDCT solar cells with a finger pitch of approximately 10μm can match and even outperform the ideal reference structure under the AM1.5G solar spectrum, due to reduced Shockley‐Read‐Hall recombination. At high solar concentrations, the performance of the smallest pitch DDCT structure is essentially identical with the reference structure up to 100 suns. This suggests that combining the benefits offered by the IBC design with compound semiconductors could allow the development of an entire family of more efficient solar cells.

Synergistic effect of Na and Se on CZTSe solar cells through a soft chemical process

Alkali metal can improve the chalcopyrite structured device performance. However, such alkali metal is normally doped by diffusing Na into absorber layer from soda-lime glass or by vacuum method. In this study, a soft chemical method is applied to dope Na into kesterite structured compound film. Combined by XRD, SEM, SIMS, and EDS mapping, it indicates that the NaF aqueous solution treatment provides a unique Na source, which can promote the film growth and the elements distribution, especially Se element distribution. The surface decomposition of CZTSe is suppressed because of the Na participating in crystallization at the beginning stage of the selenization process, which can improve the interface between CdS and CZTSe. The average conversion efficiency of solar cell is improved from 6.3% without such treatment to above 7.8% with such chemical treatment and the best 8.4% efficiency has been achieved for the 0.005 mol/L NaF treated CZTSe device. This facile Na aqueous solution treatment afford a unique insight and also enlarge the understanding on the Na treatment on compound semiconductor solar cells, which will promote the fabrication of chalcopyrite solar cell with high performance.

Optimization of Organic Photovoltaics Incorporating P(VDF-TrFE) Nanocrystals Prepared By Reprecipitation Method

Organic photovoltaics (OPVs) cells are spotlighted as a one of the candidates for future energy source owing to their flexibility, low-cost and high-performance [ref. 1]. In a relatively short period, the power conversions (PCEs) of OPVs have achieved over 11% so that a variety of the recent researches such as improvement in molecular design and synthesis of new polymers and in improved solar cell device design has been successfully conducted to improve the OPVs performances. However, PCEs of other kinds of solar cells such as silicon solar cell and compound semiconductor solar cell have already reached over 20%. The reason why PCEs of OPVs is lower than one of the others is a recombination of carriers by Coulomb force, which is one of the biggest issues in OPVs. In many of the most efficient polymer-fullerene OPVs devices, 50% or more of the energy loss is caused by the recombination of carriers [ref. 2]. Recently, several reports to solve this problem have been reported. One of the promising ways is incorporating Ferroelectric co-polymer poly(vinylidenefluoride-trifluoroethylene) (P(VDF-TrFE)) between an active layer and electrode interface as a Langmuir-Blodgett films in OPV [ref. 3]. Ferroelectric polymers show electric field derived from its spontaneous polarization due to difference in electronegativity of fluorine and hydrogen. It is therefore possible to enhance in charge separation efficiency and carrier mobility of electron for suppression of recombination. In this research, we have successfully prepared P(VDF-TrFE) nanocrystals as s dispersion state by the reprecipitation method so that we could incorporate the nanocrystals in active layer in OPV [ref. 4]. P(VDF-TrFE) nanocrystals prepared by this method are approximately 40 nm. The obtained dispersion was mixed to dissolve with photoactive materials (P3HT : PCBM) at ratio of 15.0 : 10.5 by weight instead of a pure solvent. Moreover, the mixed solution was applied for OPV cells as an active layer. Short-circuit current (Jsc) and PCEs of OPV incorporating P(VDF-TrFE) nanocrystals was improved in at most 20% and 40%, respectively comparing to the one without P(VDF-TrFE) nanocrystals. The electric field derived from P(VDF-TrFE) nanocrystals and carrier mobility were estimated from J-V curve and calculation, respectively. Incident photo to current conversion efficiency (IPCE) of OPVs cells which are incorporating P(VDF-TrFE) was three times as high as the one which was not incorporating P(VDF-TrFE) although they had almost same absorbance and peak positions. Therefore, it was confirmed that P(VDF-TrFE) improved in charge separation efficiency and carrier mobility of electron, but not influenced light absorption. The details in experimental conditions and characteristics of P(VDF-TrFE) nanocrystals and OPVs, morphology and so on will be discussed in this presentation.

(Invited) Soft/Hard Interface for Energy Materials and Skin-like Electronics Toward Healthcare Monitoring

Power supply represents a critical challenge in the development of body-integrated electronic technologies. Although recent research establishes an impressive variety of options in energy storage (batteries and supercapacitors) and generation (triboelectric, piezoelectric, thermoelectric, and photovoltaic devices), the modest electrical performance and/or the absence of soft, biocompatible mechanical properties limit their practical use. The results presented here form the basis of soft, skin-compatible means for efficient photovoltaic generation and high-capacity storage of electrical power using dual-junction, compound semiconductor solar cells and chip-scale, rechargeable lithium-ion batteries, respectively. Miniaturized components, deformable interconnects, optimized array layouts, and dual-composition elastomer substrates, superstrates, and encapsulation layers represent key features. Systematic studies of the materials and mechanics identify optimized designs, including unusual configurations that exploit a folded, multilayer construct to improve the functional density without adversely affecting the soft, stretchable characteristics. System-level examples exploit such technologies in fully wireless sensors for precision skin thermography, with capabilities in continuous data logging and local processing, validated through demonstrations on volunteer subjects in various realistic scenarios.

Application of III-V Compound Semiconductor Solar Cell for High Efficiency Optical Wireless Power Transmission

Application of III-V Compound Semiconductor Solar Cell for High Efficiency Optical Wireless Power Transmission

The Stability Effect of Atomic Layer Deposition (ALD) of Al<sub>2</sub>O<sub>3</sub> on CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> Perovskite Solar Cell Fabricated by Vapor Deposition

The perovskite solar cells (PSCs) with Al2O3 passivation layer were fabricated and characterized. The PSC have some advantages of easier and cheaper fabrication process than that of conventional Si solar cells, III-V compound semiconductor solar cells, and organic solar cells. The perovskite light harvester, CH3NH3PbI3, was deposited by vapor deposition on [compact TiO2 / F-doped tin oxide (FTO) / glass]. The advantage of vapor deposition over solution process is expected to be able to offer the thin film with smoother surface over larger area. Then, Al2O3 passivation layer was deposited by atomic layer deposition (ALD) on the CH3NH3PbI3 light harvester. Al2O3 passivation layer was expected to prevent the CH3NH3PbI3 light harvester from oxidation and improve the solar cell efficiency, and ALD has been one of the most effective methods to deposit Al2O3 thin film for last 25 years. The atomic layer deposited Al2O3 layer thickness was optimized from the solar cell characterization. The optimized power conversion efficiency (PCE) and Al2O3 thickness were ~8.0 % and ~10.0 nm, respectively.

Flexible space solar cell array with radiation shield fabricated by guided-printing of cover glasses

As the main electrical power source of spacecraft, solar cells require high electrical performance and light weight, to provide enough electrical power for missions in space and to lower costs for launching. Multi-junction compound semiconductor solar cells generate relatively high power, but their rigid substrates are tens or hundreds of times thicker than the solar cells. In this paper, methods are described to realize flexible space solar cell arrays that can be wrapped on non-planar surfaces, by removing the rigid substrates and integrating the thin solar cells on flexible substrates. Cover glasses were integrated over the solar cells on flexible substrates through an guided-printing method, providing both flexibility and radiation shielding. Experimental results and mechanical analysis demonstrate the mechanical and electrical performances of these flexible space solar cell arrays.

Soft, thin skin-mounted power management systems and their use in wireless thermography

Power supply represents a critical challenge in the development of body-integrated electronic technologies. Although recent research establishes an impressive variety of options in energy storage (batteries and supercapacitors) and generation (triboelectric, piezoelectric, thermoelectric, and photovoltaic devices), the modest electrical performance and/or the absence of soft, biocompatible mechanical properties limit their practical use. The results presented here form the basis of soft, skin-compatible means for efficient photovoltaic generation and high-capacity storage of electrical power using dual-junction, compound semiconductor solar cells and chip-scale, rechargeable lithium-ion batteries, respectively. Miniaturized components, deformable interconnects, optimized array layouts, and dual-composition elastomer substrates, superstrates, and encapsulation layers represent key features. Systematic studies of the materials and mechanics identify optimized designs, including unusual configurations that exploit a folded, multilayer construct to improve the functional density without adversely affecting the soft, stretchable characteristics. System-level examples exploit such technologies in fully wireless sensors for precision skin thermography, with capabilities in continuous data logging and local processing, validated through demonstrations on volunteer subjects in various realistic scenarios.

Technical Tasks and Development Current Status of Organic Solar Cells

Serious environmental problems have been caused by the greenhouse effect due to carbon dioxide(CO2) or nitrogen oxides(NOx) generated by the use of fossil fuels, including oil and liquefied natural gas. Many countries, including our own, the United States, those of the European Union and other developed countries around the world; have shown growing interest in clean energy, and have been concentrating on the development of new energy-saving materials and devices. Typical non-fossil-fuel sources include solar cells, wind power, tidal power, nuclear power, and fuel cells. In particular, organic solar cells(OSCs) have relatively low power-conversion efficiency(PCE) in comparison with inorganic(silicon) based solar cells, compound semiconductor solar cells and the CIGS [Cu(In1-xGax)Se2] thin film solar cells. Recently, organic cell efficiencies greater than 10 % have been obtained by means of the development of new organic semiconducting materials, which feature improvements in crystalline properties, as well as in the quantum-dot nano-structure of the active layers. In this paper, a brief overview of solar cells in general is presented. In particular, the current development status of the next-generation OSCs including their operation principle, device-manufacturing processes, and improvements in the PCE are described.

A GaAs/GaInP dual junction solar cell grown by molecular beam epitaxy

We report the recent result of GaAs/GaInP dual-junction solar cells grown by all solid-state molecular-beam-epitaxy (MBE). The device structure consists of a GaIn0.48P homojunction grown epitaxially upon a GaAs homojunction, with an interconnected GaAs tunnel junction. A photovoltaic conversion efficiency of 27% under the AM1.5 globe light intensity is realized for a GaAs/GaInP dual-junction solar cell, while the efficiencies of 26% and 16.6% are reached for a GaAs bottom cell and a GaInP top cell, respectively. The energy loss mechanism of our GaAs/GaInP tandem dual-junction solar cells is discussed. It is demonstrated that the MBE-grown phosphide-containing III—V compound semiconductor solar cell is very promising for achieving high energy conversion efficiency.

Preface: Advanced Silicon Materials Research for Electronic and Photovoltaic Applications

Preface: Advanced Silicon Materials Research for Electronic and Photovoltaic Applications

Cover Picture: Properties of nitride‐based photovoltaic cells under concentrated light illumination (Phys. Status Solidi RRL 4/2012)

One of the disadvantages of compound semiconductor solar cells is their high cost compared with silicon or organic solar cells. This problem can be solved by using a condenser lens system. Thus, if the solar cells can operate at 200 suns, the cost per chip would be reduced considerably. In their Letter on pp. 145–147, Yamamoto et al. report on the focusing properties of nitride-based solar cells up to 200 suns and also discuss the dependence of solar cell characteristics on concentration ratio. The structure of the devices prepared in this study consists of 50 pairs of unintentionally doped Ga0.83In0.17N/Ga0.93In0.07N superlattice layers as active layers on freestanding GaN substrate. Another 10 pairs of Si-doped Ga0.90In0.10N/GaN superlattice layers were inserted beneath the active layers in order to reduce the dislocation density. These nitride-based solar cells operate effectively even at 200 suns, their conversion efficiency of 3.4% is the highest ever reported value for nitride solar cells.

High-efficiency GaAs and GaInP solar cells grown by all solid-state molecular-beam-epitaxy

We report the initial results of GaAs and GaInP solar cells grown by all solid-state molecular-beam-epitaxy (MBE) technique. For GaAs single-junction solar cell, with the application of AlInP as the window layer and GaInP as the back surface field layer, the photovoltaic conversion efficiency of 26% at one sun concentration and air mass 1.5 global (AM1.5G) is realized. The efficiency of 16.4% is also reached for GaInP solar cell. Our results demonstrate that the MBE-grown phosphide-contained III-V compound semiconductor solar cell can be quite comparable to the metal-organic-chemical-vapor-deposition-grown high-efficiency solar cell.

Triple junction InGaP/InGaAs/Ge solar cells for high concentration photovoltaics application: Degradation tests of solar receivers

Today, the III–V compound semiconductor solar cells represent the most promising photovoltaic technology to achieve the grid parity, thanks to their proven capability to work at high concentration factors (H-CPV: high concentration photovoltaics) with demonstrated conversion efficiencies higher than 40% in the spectral conditions typical of the Earth surface (AM1.5D). One of the issues to be investigated in the H-CPV systems is the reliability of the solar cell receivers. In fact in concentration conditions the thermal and mechanical stress on the solar cell, mounted on receivers, is very significant with respect to flat panel technology. This paper proposes a method, typically used in the LED industry, to test, in accelerated conditions, the H-CPV solar receivers. The receivers, based on III–V solar cells, size 2.1 × 2.1 mm 2 from CESI, were built by chip on board technology at CRP labs, and characterized for 800 h to simulate 20 years of in-field operation in concentration regime (500×).

A tapered dielectric waveguide solar concentrator for a compound semiconductor photovoltaic cell

A novel tapered dielectric waveguide solar concentrator is proposed for compound semiconductor solar cells utilizing optical fiber preform. Its light collecting capability is numerically simulated and experimentally demonstrated for feasibility and potential assessments. Utilizing tapered shape of an optical fiber preform with a step-index profile, low loss guidance was enhanced and the limitation in the acceptance angle of solar radiation was alleviated by an order of magnitude. Using a solar simulator the device performances were experimentally investigated and discussed in terms of the photocurrent improvements. Total acceptance angle exceeding +/- 6 degrees was experimentally achieved sustaining a high solar flux.

Fabrication and Characterization of Copper System Compound Semiconductor Solar Cells

Copper system compound semiconductor solar cells were produced by a spin-coating method, and their cell performance and structures were investigated. Copper indium disulfide- (CIS-) based solar cells with titanium dioxide (TiO2) were produced on F-dopedSnO2(FTO). A device based on an FTO/CIS/TiO2structure provided better cell performance compared to that based on FTO/TiO2/CIS structure. Cupric oxide- (CuO-) and cuprous oxide- (Cu2O-) based solar cells with fullerene (C60) were also fabricated on FTO and indium tin oxide (ITO). The microstructure and cell performance of the CuO/C60heterojunction and theCu2O:C60bulk heterojunction structure were investigated. The photovoltaic devices based on FTO/CuO/C60and ITO/Cu2O:C60structures provided short-circuit current density of 0.015 mAcm−2and 0.11 mAcm−2, and open-circuit voltage of 0.045 V and 0.17 V under an Air Mass 1.5 illumination, respectively. The microstructures of the active layers were examined by X-ray diffraction and transmission electron microscopy.

New application of Cat-CVD technology and recent status of industrial implementation

Recent progress in application of Cat-CVD (Hot Wire CVD) technology is overviewed, along with recent status of industrial implementation of this technology. Although the use of Cat-CVD technology in factories has not been open to the public, the technology appears to fit for the fabrication of ultra-high frequency devices of compound semiconductors, compound semiconductor lasers, solar cells, and formation of coating films for other devices. The issues for practical use of this technology are also discussed, together with promising future of this Cat-CVD technology.

InGaAs Solar Cells Grown on Wafer-Bonded InP/Si Epitaxial Templates

AbstractInP/Si engineered substrates formed by wafer bonding and layer transfer have the potential to significantly reduce the cost and weight of III-V compound semiconductor solar cells. InP/Si substrates were prepared by He implantation of InP prior to bonding to a thermally oxidized Si substrate and annealing to exfoliate an InP thin film. Following thinning to remove damage caused by the implantation and exfoliation from the surface of the InP transferred film, InGaAs solar cells lattice-matched to bulk InP were grown on those substrates using metal-organic chemical vapor deposition. The photovoltaic current-voltage characteristics of the InGaAs cells fabricated on the wafer-bonded InP/Si substrates were comparable to those synthesized on commercially available epi-ready InP substrates, thus providing an initial demonstration of wafer-bonded InP/Si substrates as an alternative to bulk InP substrates for solar cell applications.