Degradation modeling of InGaP/GaAs/Ge triple-junction solar cells irradiated with various-energy protons

Degradation modeling of InGaP/GaAs/Ge triple-junction (3J) solar cells subjected to proton irradiation is performed with the use of a one-dimensional optical device simulator, PC1D. By fitting the external quantum efficiencies of 3J solar cells degraded by 30 keV, 150 keV, 3 MeV, or 10 MeV protons, the short-circuit currents (I_SC) and open-circuit voltages (V_OC) are simulated. The damage coefficients of minority carrier diffusion length (K_L) and the carrier removal rate of base carrier concentration (R_C) of each sub-cell are also estimated. The values of I_SC and V_OC obtained from the calculations show good agreement with experimental values at an accuracy of 5%. These results confirm that the degradation modeling method developed in this study is effective for the lifetime prediction of 3J solar cells.     

5–20 MeV proton irradiation effects on GaAs/Ge solar cells for space use

This paper reports the high-energy proton irradiation effects on GaAs/Ge space solar cells. The solar cells were irradiated by protons with energy of 5–20 MeV at a fluence ranging from 1×10⁹ to 7×10¹³ cm⁻², and then their electric parameters were measured at AM0. It was shown that the I_sc, V_oc and P_max degrade as the fluence increases, respectively, but the degradation rates of I_sc, V_oc and P_max decrease as the proton energy increases, and the degradation is relative to proton irradiation-induced defect Ec−0.41 eV in irradiated GaAs/Ge cells.     

Low-energy proton irradiation effects on GaAs/Ge solar cells

This paper reports the low-energy proton irradiation effects on GaAs/Ge solar cells for space use. The proton irradiation experiments were performed with a fluence of 1.2×10¹³ cm⁻², energies ranging from 0.1 to 3.0 MeV. The results obtained demonstrate that the irradiation with a proton energy of 0.3 MeV gives rise to the most degradation rates of I_sc, V_oc and P_max of the solar cells with no coverglass, which is related to the proton irradiation-induced vacancies near the pn junction in GaAs/Ge cells. The degradation rates of I_sc, V_oc and P_max of the solar cells with coverglass increase as the proton energy increases due to the cascade ions induced by collision processes. It is found that the coverglass has an obvious protection effect against the irradiation with the proton energy below 0.5 MeV.     

Performance study of solar cell arrays based on a Trough Concentrating Photovoltaic/Thermal system

The performances of solar cell arrays based on a Trough Concentrating Photovoltaic/Thermal (TCPV/T) system have been studied via both experiment and theoretical calculation. The I–V characteristics of the solar cell arrays and the output performances of the TCPV/T system demonstrated that among the investigated four types of solar cell arrays, the triple junction GaAs cells possessed good performance characteristics and the polysilicon cells exhibited poor performance characteristics under concentrating conditions. The optimum concentration ratios for the single crystalline silicon cell, the Super cells and the GaAs cells were also studied by experiments. The optimum concentration ratios for the single crystalline silicon cells and Super cells were 4.23 and 8.46 respectively, and the triple junction GaAs cells could work well at higher concentration ratio. Besides, some theoretical calculations and experiments were performed to explore the influences of the series resistances and the working temperature. When the series resistances R_s changed from 0 Ω to 1 Ω, the maximum power P_m of the single crystalline silicon, the polycrystalline silicon, the Super cell and the GaAs cell arrays decreased by 67.78%, 74.93%, 77.30% and 58.07% respectively. When the cell temperature increased by 1 K, the short circuit current of the four types of solar cell arrays decreased by 0.11818 A, 0.05364 A, 0.01387 A and 0.00215 A respectively. The research results demonstrated that the output performance of the solar cell arrays with lower series resistance was better and the working temperature had a negative impact on the current under concentration. In addition, solar irradiation intensity had certain effects on the solar cell’s performance. For the crystalline silicon solar cell arrays, when the solar direct radiation exceeded a certain value, the I–V curves almost became a straight line and the output performances decreased due to the high series resistance leading to the high power loss. For the triple junction GaAs solar cell array, its performance was always excellent.     

High-voltage (1.8 V) tandem solar cell system using a GaAs/AlXGa(1−X)As graded solar cell and dye-sensitised solar cells with organic dyes having different absorption spectra

Stacked multijunction (tandem) solar cells have been prepared by mechanically stacking dye-sensitised solar cells (DSCs) and a GaAs/Al_XGa_(1−X)As graded solar cell (GGC) as the top and bottom cells, respectively. Three organic dyes with different absorption spectra (D131, D102 and D205) were used in the DSCs, in order to match the photocurrent density between the DSC and the GGC. Tuning the absorption range of the DSC by choosing an appropriate dye, increased the overall photovoltaic conversion efficiency due to the optimal utilisation of the solar spectrum in the individual cells. The open circuit photovoltages (V_OC) of the GGC and the DSC with D131 were 1.11 V and 0.76 V, respectively, resulting in a V_OC of 1.85 V and a photovoltaic conversion efficiency of 7.63% for the tandem cell. Although the overall conversion efficiency has not exceeded that of the GGC (7.66%), these tandem cells provide adequate V_OC values for water splitting applications.     

Numerical simulation of the effect of the Al molar fraction and thickness of an AlxGa1−xAs window on the sensitivity of a p+–n–n+ GaAs solar cell to 1 MeV electron irradiation

In this paper numerical simulation has been used to predict the effect of the thickness and aluminium (Al) mole fraction of an AlGaAs layer, used as a window for a p⁺–n–n⁺ GaAs solar cell under AM0 illumination and exposed to 1 MeV electron irradiation. Such solar cells are used in satellites and undergo severe degradation in their performance due to induced structural defects. The irradiation-induced defects are modelled as energy levels in the energy gap of GaAs. To predict this effect, the spectral response is evaluated for different electron irradiation fluences for two types of cells. In the first a narrow Al_0.31Ga_0.69As window is a small part of the p⁺ layer while in the second type the whole window is an Al_xGa_1?xAs layer with a gradual Al mole fraction. The obtained results show that the Al_xGa_1?xAs window with a gradual Al mole fraction improves the resistance of the solar cell to electron irradiation especially in the short wavelengths range.     

Recent developments in high-efficiency Ga0.5In0.5P/GaAs/Ge dual- and triple-junction solar cells: steps to next-generation PV cells

Dual-junction Ga_0.5In_0.5P/GaAs solar cells on Ge substrates have rapidly gone from small, high-efficiency laboratory cells, to large-area, high-efficiency cells manufactured at Spectrolab in high volume. Over 500,000 of these dual-junction (DJ) cells with 27-cm² area have been produced, with average AM0 load point efficiency of 21.4%. The next step in the evolution of this type of multijunction solar cell has been taken, with the development of triple-junction (TJ) Ga_0.5In_0.5P/GaAs/Ge cells. The addition of the germanium third junction, plus several significant improvements in the device structure, have led to a measured efficiency of 27.0% (AM0, 28°C) at Spectrolab on large-area (>30 cm²) TJ cells. The TJ cell is now in production at Spectrolab. Ga_0.5In_0.5P/GaAs/Ge cells are viable not only for non-concentrating space applications, but also for terrestrial and space concentrator systems. Efficiencies up to 32.3% at 47 suns under the terrestrial AM1.5D spectrum have been achieved.     

Phase stability and electrical conductivity of Ca-doped LaNb1−xTaxO4−δ high temperature proton conductors

The electrical conductivity, crystal structure and phase stability of La_0.99Ca_0.01Nb_1−xTa_xO_4−δ (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5, δ = 0.005), a potential candidate for proton conductor for solid oxide fuel cells (SOFCs), have been investigated using AC impedance technique and in situ X-ray powder diffraction. Partially substituting Nb with Ta elevates the phase transition temperature (from a monoclinic to a tetragonal structure) from ∼520 °C for x = 0 to above 800 °C for x = 0.4. AC conductivity of the La_0.99Ca_0.01Nb_1−xTa_xO_4−δ both in dry and wet air decreased slightly with increasing Ta content above 750 °C, while below 500 °C, it decreased by nearly one order of magnitude for x = 0.4. It was also determined that the activation energy for the total conductivity increases with increasing Ta content from 0.50 eV (x = 0) to 0.58 eV (x = 0.3) for the tetragonal phase, while it decreases with increasing Ta content from 1.18 eV (x = 0) to 1.08 eV (x = 0.4) for the monoclinic phase. By removing the detrimental structural phase transition from the intermediate-temperature range, consequently avoiding the severe thermal expansion problem up to 800 °C, partial substitution of Nb with Ta brings this class of material closer to its application in electrode-supported thin-film intermediate-temperature SOFCs.     

Wide-gap a-Si1−xCx:H solar cells with high light-induced stability for multijunction structure applications

Light-induced stability of various p-i-n type wide-gap a-Si_1−xC_x:H solar cells has been systematically investigated. The i-layers of all a-Si_1−xC_x:H solar cells were prepared using a 60 MHz VHF-PECVD technique with monomethyl silane (SiH₃CH₃, MMS) as the carbon source. It was confirmed that device structures, especially the type of buffer layer and thickness of i-layer, strongly affect the degradation behavior of a-Si_1−xC_x:H solar cells. The fabricated a-Si_1−xC_x:H solar cells showed efficiency degradation of about 11-22% depending on device structure. Efficiency degradation of optimized a-Si_1−xC_x:H solar cells was much better compared with those reported by other groups even with thinner i-layer. These results revealed that a-Si_1−xC_x:H solar cells with optimized buffer layer and prepared using MMS as the carbon source have high light-induced stability. Moreover, we have also fabricated a-Si_1−xC_x:H/a-Si:H tandem cells with a SiO_x intermediate layer to examine the benefit of a-Si_1−xC_x:H top cells. Up to now, V_oc as high as 1.81 V and fill factor (FF) as high as 0.70 have been achieved. Thus, the fabricated a-Si_1−xC_x:H solar cell is promising to be used as the top cell in multijunction solar cells.     

The study on high efficient AlxGa1−xAs/GaAs solar cells

The investigation of Al_xGa_1−xAs/GaAs solar cells is carried out by means of both metalorganic chemical vapor deposition (MOCVD) and liquid-phase epitaxial (LPE) technique. The measurements of illuminated I–V characteristics, dark I–V characteristics and quantum efficiencies were performed for the GaAs solar cells made in author's laboratory. The measuring results revealed that the quality of materials in GaAs solar cell's structures is the key factor for getting high-efficient GaAs solar cells, but the effect of post-growth technology on the performances of GaAs solar cells is also very strong. The 21.95% (AM0, 2×27 cm², 25°C) high conversion efficiency in a typical GaAs solar cell has been achieved owing to improving the quality of materials as well as optimizing the post-growth technology of devices.     

Dye-sensitized, nano-porous TiO2 solar cell with poly(acrylonitrile): MgI2 plasticized electrolyte

Dye-sensitized solar cells are promising candidates as supplementary power sources; the dominance in the photovoltaic field of inorganic solid-state junction devices is in fact now being challenged by the third generation of solar cells based on dye-sensitized, nano-porous photo-electrodes and polymer electrolytes. Polymer electrolytes are actually very favorable for photo-electrochemical solar cells and in this study poly(acrylonitrile)-MgI₂ based complexes are used. As ambient temperature conductivity of poly(acrylonitrile)-salt complexes are in general low, a conductivity enhancement is attained by blending with the plasticizers ethylene carbonate and propylene carbonate. At 20 °C the optimum ionic conductivity of 1.9 × 10⁻³ S cm⁻¹ is obtained for the (PAN)₁₀(MgI₂)_n(I₂)_n/10(EC)₂₀(PC)₂₀ electrolyte where n = 1.5. The predominantly ionic nature of the electrolyte is seen from the DC polarization data. Differential scanning calorimetric thermograms of electrolyte samples with different MgI₂ concentrations were studied and glass transition temperatures were determined. Further, in this study, a dye-sensitized solar cell structure was fabricated with the configuration Glass/FTO/TiO₂/Dye/Electrolyte/Pt/FTO/Glass and an overall energy conversion efficiency of 2.5% was achieved under solar irradiation of 600 W m⁻². The I-V characteristics curves revealed that the short-circuit current, open-circuit voltage and fill factor of the cell are 3.87 mA, 659 mV and 59.0%, respectively.     

Evaluation of temperature characteristics of high-efficiency InGaP/InGaAs/Ge triple-junction solar cells under concentration

Temperature characteristics of the open-circuit voltage (V_oc) were investigated in the temperature range from 30°C to 240°C for the InGaP/InGaAs/Ge triple-junction cells. Also, single-junction cells that had the similar structure to the subcells in the triple-junction cells were studied. In the high-temperature range (from 170°C to 240°C), the temperature coefficients of V_oc of the InGaP/InGaAs/Ge triple-junction solar cell (dV_oc/dT) were different from those in the low-temperature range (from 30°C to 100°C). This is because photo-voltage from the Ge subcell becomes almost 0 V in the high-temperature range. It was found that the open-circuit voltage of a Ge single-junction cell reduced to almost 0 V temperatures over 120°C under 1 sun condition.     

Stoichiometry controlled conversion efficiency in nanostructured heterojunction solar cell of CdS/CuInSXSe2−X grown by chemical ion exchange method at room temperature

Here in the present paper, we report on growth of stoichiometric and nonstoichiometric nanostructured heterojunction solar cell of CdS/CuInS_XSe_2-X varying X from 0 to 2 in the interval of 0.5 using cost effective, simple, chemical ion exchange method at room temperature on ITO glass substrate. The as-grown varying composition solar cells annealed at 200 °C in air and characterized for structural, compositional, optical and illumination studies. The X-ray diffraction pattern obtained from CdS/CuInS_XSe_2-X solar cell confirms the formation of CuInSe₂, CuInS_0.5Se_1.5, CuInS₁Se₁, CuInS_1.5Se_0.5 and CuInS₂ phases having tetragonal structure with varying crystallite size from 19, 19.37, 28, 33 and 20 nm respectively. The energy dispersive X-ray analysis (EDAX) confirms the expected elemental composition in the heterojunction solar cell. Optical absorbance analysis confirms composition controlled electronic transitions in the thin films while energy band gap observed to be red shifted with increase the value of X. The solar energy conversion efficiency achieved upon illuminating to 100 mW/cm² observed to be 0.27%, 0.06%, 0.17%, 0.02% and 0.23% for CuInSe₂, CuInS_0.5Se_1.5, CuInS₁Se₁, CuInS_1.5Se_0.5 and CuInS₂ respectively, which correspond for stoichiometric dependent electron-hole pair generation and separation phenomenon.     

p-Cu2O/n-ZnO heterojunction applied to visible light Orange II degradation

The p-Cu₂O/n-ZnO system is studied for its potential use as a photoactive heterojunction able to highly perform under visible light. The main application deals with the degradation of organic dyes such as Orange II and the effects of Cu₂O amount, Orange II concentration and light intensity are investigated. Results show that the kinetics of degradation follows a pseudo-first order and the optimum sensitization effect is obtained using a 70% concentration of Cu₂O. The degradation rate reaches its maximum (R_initial = 22.45 × 10⁻² mg l⁻¹ min⁻¹) at 15 mg l⁻¹ of Orange II. The effect of the irradiation intensity is also investigated taking the electrical energy consumption per order of magnitude (EE/O) as a figure of merit. The highest efficiency is obtained at an irradiation intensity of ∼122 × 10⁻⁵ kW with k_OBS = 14.97 × 10⁻³ min⁻¹ and EE/O, which corresponds to 12.54 kW h m⁻³ of energy consumption. This heterojunction allows a ∼25% saving of electrical energy in comparison to the p-Cu₂O/n-TiO₂ system, demonstrating the important role of the collector.     

Sintering and conductivity of BaCe0.9Y0.1O2.95 synthesized by the sol-gel method

Ceramic powders of BaCe_0.9Y_0.1O_2.95 (BCY10) have been prepared by the sol-gel method. Barium and yttrium acetate and cerium nitrate were used as ceramic precursors in a water solution. The reaction process studied by DTA-TG and XRD showed that calcination of the precursor powder at T ≥ 1000 °C produces a single perovskite phase. The densification behaviour of green compacts studied by constant heating rate dilatometry revealed that the shrinkage rate was maximal at 1430 °C. Sintered densities higher than 95% of the theoretical one were thus obtained below 1500 °C. The bulk and additional blocking effects were characterized by impedance spectroscopy in wet atmosphere between 150 and 600 °C. A proton conduction behaviour was clearly identified. The blocking effect can be related to a space-charge depletion layer of protons in the vicinity of grain boundaries.     

Cadmium ion soaking treatment for solution processed CuInSxSe2−x solar cells and its effect on defect properties

Recombination of charge carriers due to electronically active material defects is one of the major factors limiting power conversion efficiency in solar cells. We have studied the defect behavior in CuInS_xSe_2−x solar cells fabricated through a solution process with a maximum heating temperature of 390 °C. By introducing a cadmium ion soaking step into the fabrication process, we find that the recombination rate can be reduced. Through the use of capacitance-voltage (C-V) profiling, drive level capacitance profiling (DLCP) and admittance spectroscopy analysis, the cadmium ion soaking process was found to increase the charge carrier concentration in the bulk of the absorber, and shift the energy level of the N1 defect toward the valence band edge. The soaking process was found to most obviously affect the open circuit voltage with an average improvement of 33 mV.     

Novel BaCe0.7In0.2Yb0.1O3−δ proton conductor as electrolyte for intermediate temperature solid oxide fuel cells

Novel proton conductor BaCe_0.7In_0.2Yb_0.1O_3−δ (BCIYb) has been successfully synthesized by a modified Pechini method and characterized as electrolyte for intermediate temperature solid oxide fuel cells. Acceptable tolerance to wet CO₂ environment was found during chemical stability tests. No interaction between the BCIYb electrolyte and La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ (LSCF) cathode was observed during the cathode fabrication process. Further, no detectable impurity phase was found when the BCIYb-LSCF mixed powders were calcined at 700 °C for 50 h. BCIYb dense samples sintered at 1450 °C for 5 h showed acceptable conductivities of 7.2 × 10⁻³, 8 × 10⁻³, 4.5 × 10⁻³ and 3.1 × 10⁻³ S cm⁻¹ at 800 °C in dry air, wet air, wet H₂ and wet N₂, respectively. The maximum cell power outputs of single cells with the configuration of Ni-BaZr_0.1Ce_0.7Y_0.2O_3−δ (BZCY)|BCIYb|BZCY-LSCF were 0.15, 0.218 and 0.28 W cm⁻² at 600, 650 and 700 °C, respectively. No cell degradation was observed for cells operated at a constant voltage of 0.7 V in the 25 h short-term durability test.     

Highly enhanced p-type electrical conduction in wide band gap Cu1+xAl1−xS2 polycrystals

As potential critical p-type transparency electrode materials applied in solar cells, a series of the Cu- and Zn-doped CuAlS₂ samples with band gaps over 3 eV have been prepared, and their optical and electrical properties have been thoroughly investigated. Conductivities as high as 250 S cm⁻¹ are achieved at a Cu doping level of 8 mol%, which are among the highest values known for p-type transparent materials and sufficient for collecting holes in solar cells. A high mobility of 21.2 cm² V⁻¹ s⁻¹ is also reached at the same doping level. The origin of conductivity enhancement by Cu doping and the structure-optoelectrical property relationship has been elucidated.     

Ionic conduction in Sn1−xScxP2O7 for intermediate temperature fuel cells

A novel series of mixed ion conductors, Sn_1−xSc_xP₂O₇ (x = 0.03, 0.06, 0.09, 0.12), were synthesized by a solid-state reaction method. The conduction behaviors of the ion conductors in wet hydrogen atmosphere were investigated by some electrochemical methods including AC impedance spectroscopy, gas concentration cells in the temperature range of 323-523 K. It was found that the doping limit of Sc³⁺ in SnP₂O₇ was between 9 mol% and 12 mol%. The highest conductivity was observed to be 2.76 × 10⁻² S cm⁻¹ for the sample of x = 0.06 under wet H₂ atmosphere at 473 K. The ionic conduction was contributed mainly to proton and partially to oxide ion in wet hydrogen atmosphere from 373 K to 523 K. The H₂/air fuel cells using Sn_1−xSc_xP₂O₇ (x = 0.03, 0.06, 0.09) as electrolytes (1.7 mm in thickness) generated the maximum power densities of 11.16 mW cm⁻² for x = 0.03, 25.02 mW cm⁻² for x = 0.06 and 14.34 mW cm⁻² for x = 0.09 at 423 K, respectively. The results indicated that Sn_1−xSc_xP₂O₇ is a promising solid electrolyte system for intermediate temperature fuel cells.