Dual-junction Solar Cells Research Articles

Performance Optimization of the InGaP/GaAs Dual-Junction Solar Cell Using SILVACO TCAD

In this work, an optimization of the InGaP/GaAs dual-junction (DJ) solar cell performance is presented. Firstly, a design for the DJ solar cell based on the GaAs tunnel diode is provided. Secondly, the used device simulator is calibrated with recent experimental results of an InGaP/GaAs DJ solar cell. After that, the optimization of the DJ solar cell performance is carried out for two different materials of the top window layer, AlGaAs and AlGaInP. For AlGaAs, the optimization is carried out for the following: aluminum (Al) mole fraction, top window thickness, top base thickness, and bottom BSF doping and thickness. The electrical performance parameters of the optimized cell are extracted: J SC = 18.23 mA / c m 2 , V OC = 2.33 V , FF = 86.42 % , and the conversion efficiency ( η c ) equals 36.71%. By using AlGaInP as a top cell window, the electrical performance parameters for the optimized cell are J SC = 19.84 mA / c m 2 , V OC = 2.32 V , FF = 83.9 % , and η c = 38.53 % . So, AlGaInP is found to be the optimum material for the InGaP/GaAs DJ cell top window layer as it gives 4% higher conversion efficiency under 1 sun of the standard AM1.5G solar spectrum at 300 K in comparison with recent literature results. All optimization steps and simulation results are carried out using the SLVACO TCAD tool.

Investigation of the Carrier Movement through the Tunneling Junction in the InGaP/GaAs Dual Junction Solar Cell Using the Electrically and Optically Biased Photoreflectance Spectroscopy

For examining the carrier movements through tunnel junction, electrically and optically-biased photoreflectance spectroscopy (EBPR and OBPR) were used to investigate the internal electric field in the InGaP/GaAs dual junction solar cell at room temperature. At InGaP and GaAs, the strength of p-n junction electric fields (Fpn) was perturbed by the external DC bias voltage and CW light intensity for EBPR and OBPR experiments, respectively. Moreover, the Fpn was evaluated using the Fast Fourier Transform (FFT) of the Franz—Keldysh oscillation from PR spectra. In the EBPR, the electric field decreased by increasing the DC bias voltage, which also decreased the potential barrier. In OBPR, when incident CW light is absorbed by the top cell, the decrement of the Fpn in the GaAs cell indicates that the photogenerated carriers are accumulated near the p-n junction. Photogenerated carriers in InGaP can pass through the tunnel junction, and the PR results show the contribution of the modification of the electric field by the photogenerated carriers in each cell. We suggest that PR spectroscopy with optical-bias and electrical-bias could be analyzed using the information of the photogenerated carrier passed through the tunnel junction.

THEORETICAL SIMULATION OF THE EFFECT OF TEMPERATURE OF MULTI-JUNCTION SOLAR CELLS (PIN/ InGaN)

In this study, we performed a numerical theoretical simulation of single-junction and dualjunction solar cells based on InGaN. This simulation calculates the electrical parameters, characteristics of each of the studied cells, such as absorption, open-circuit voltage (Vco), collection efficiency, short circuit density (Jsc), and form factor FF. We have optimized the cells top PIN (In0.62Ga0.38N) and bottom PIN (In0.81Ga0.19N), and a dual-junction cell. The conversation efficiency of the single junction PIN cells exceeds 23%, while it is 38% for the dual-junction cell. The temperature dependencies of single junction and dual-junction solar cells have been studied at temperatures ranging from 300˚K to 450˚K. The variation of the electrical parameters of each cell was simulated with increasing temperature and the simulation result was detailed in this study. This study was done under standard conditions (AM1.5, 1000mW/cm2 ) and the simulation was performed on an ANOC calculation code (the latter is available as an application on android devices).

An integrated GaInP/Si dual-junction solar cell with enhanced efficiency using TOPCon technology

The main focus here is to electrically connect lattice mismatched GaInP/Si sub-cells and enhance the overall cell performance of the designed dual-junction solar cell. This dual-junction solar cell is designed with carrier-selective tunnel oxide passivated contact (CS-TOPCon) technology. The lattice mismatch between the sub-cells is reduced by inserting buffer layer in the top cell. This buffer layer helps in better photogeneration and carrier transport and increases short-circuit current. The presence of electric field in the tunnel oxide region and linear behavior of the pinholes (micro-resistors) is extensively studied. GaInP and Si cells are individually simulated using Silvaco ATLAS TCAD simulation tool. The CS-TOPCon technology at the passivated bottom cell reduces the recombination and increases the external open-circuit voltage. The integrated GaInP/Si dual-junction solar cell results in the efficiency of 28.14% and the application of CS-TOPCon technology enhances the efficiency up to 35.32% using ASTM-certified globally accepted AM1.5G spectrum. The obtained result of electrically connected DJSC design is compared with available experimental data.

Proposal of CIGS dual-junction solar cell and investigation of different metal grids effect

In this report, four different metallic grid connectivity models, namely graphene, aluminum, gold, and silver for the copper gallium diselenide/copper indium gallium diselenide (CGS/CIGS) dual-junction solar cell, are discussed. In this structure, it is assumed that the metal contact with the aluminum-doped zinc oxide (ZnO:Al) layer forms an ohmic contact. This assumption is true since the metal grids are sandwiched. The sandwich metal grid is such that at first a metal layer having an ohmic contact with ZnO:Al is deposited, then the desired metal layer is placed on the metal layer as contact. In fact, this metal grid replaces the transparent conductor oxide (TCO) in the structure. Using a metal grid instead of a TCO will increase the transparency and thus be more absorbent, because the TCO also has some absorption and does not allow much light to enter the absorber layer. Based on the results of the simulation and comparison of the performance of the metal patterns, we conclude that by choosing the graphene ohmic contact, we will achieve higher efficiency and absorption. The CIGS dual-junction solar cell features were obtained by graphene metal grid, short circuit current of 14.7403 mA/cm2, open circuit voltage of 1.99054 V, fill factor of 38.78%, and efficiency of 11.38%.

Measurement Uncertainties in I–V Calibration of Multi-junction Solar Cells for Different Solar Simulators and Reference Devices

Different types of dual-junction solar cells (perovskite/silicon and GaInP/(Al)GaAs) are used in an investigation of measurement uncertainty for electrical characterization of multi-junction solar cells. A method traceable to international reference standards is presented. The spectral mismatch factor matrix is introduced and used with a Monte-Carlo method including manifold correlated and uncorrelated uncertainties. In this way, a detailed analysis of the solar simulator's spectral irradiance and its influence on uncertainty becomes possible. The use of subcell-adapted and broadband reference solar cells is addressed regarding their impact on uncertainty. This allows for finding optimal conditions for calibration with lowest measurement uncertainty. The short-circuit current of a series connected multi-junction solar cell is affected by luminescence coupling and other effects. With an experimental method it is shown how the uncertainty of the device short-circuit current can be precisely determined. The spectrometric characterization method allows deriving uncertainties of all I–V parameters. In this way a complete evaluation of measurement uncertainty for the calibration of multi-junction solar cells at standard testing conditions is introduced. This article is an extension to our work presented at the 46th IEEE PVSC. Here, we have added a detailed analysis of the influence of different solar simulator spectral irradiance distributions on measurement uncertainty by evaluating a Monte Carlo simulation introducing correlation coefficients. In addition for the first time, it is shown how luminescent coupling influences the calibration of multi-junction solar cells and how the effect needs to be implemented into the uncertainty of measurement for the short-circuit current as well as efficiency.

Large Scale Spectral Splitting Concentrator Photovoltaic System Based on Double Flat Waveguides

In this research, we present a novel design for a large scale spectral splitting concentrator photovoltaic system based on double flat waveguides. The sunlight concentrator consists of a Fresnel lens array and double waveguides. Sunlight is firstly concentrated by Fresnel lenses then reaches an upper flat waveguide (UFW). The dichroic mirror-coated prisms are positioned at each focused area to divide the sunlight spectrum into two bands. The mid-energy (mid E) band is reflected at the prism surface and coupled to the UFW. The GaInP/GaAs dual-junction solar cell is attached at the exit port of the UFW to maximize the electrical conversion efficiency of the mid E band. The low-energy (low E) band is transmitted and reaches a bottom flat waveguide (BFW). The mirror coated prisms are utilized to redirect the mid E band sunlight for coupling with the BFW. The GaInAsP/GaInAs dual-junction solar cell is applied to convert the low E band to electricity. The system was modeled using the commercial optic simulation software LightTools™. The results show that the proposed system can achieve optical efficiencies of 84.02% and 80.01% for the mid E band and low E band, respectively, and a 46.1% electrical conversion efficiency for the total system. The simulation of the system performance and comparison with other PV systems prove that our proposed design is a new approach for a highly efficient photovoltaic system.

High Doping Performance of Sulfur and Zinc Dopants in Tunnel Diodes Using Hydride Vapor Phase Epitaxy

We evaluate the performances of sulfur (S) and zinc (Zn) as n - and p -type dopants in multijunction solar cells to develop tunnel diodes (TDs) by hydride vapor phase epitaxy (HVPE). HVPE has emerged as a low-cost alternative for the fabrication of III–V solar cells. In p -GaAs, all the Zn atoms can be activated, achieving free-hole concentrations greater than 1019 cm−3. On the contrary, n -GaAs becomes saturated in free electrons at the concentration of 5 × 1018 cm−3 due to the formation of the VGa−SAs complexes. Nevertheless, GaAs TDs with excessive S incorporation at a density of 4 × 1019 cm−3 yield a peak in the tunneling-current density of 5 A/cm2. Previously, we achieved conversion efficiencies of 20.8% for GaAs cells and 12.1% for InGaP cells using a triple-chamber HVPE. By integrating these components together in a single growth process, we develop an InGaP/GaAs dual-junction solar cell with a conversion efficiency of 21.8% and a minimal voltage loss in TDs under at least 1-sun operation.

Heteroepitaxy of GaAsP and GaP on GaAs and Si by low pressure hydride vapor phase epitaxy

Direct heteroepitaxy of GaAsP and GaP on GaAs and on Si by low-pressure hydride vapor phase epitaxy (HVPE) is investigated as prior studies for photovoltaics and non-linear optics applications. When growing GaAsP on GaAs, it is found that the ambient gas during substrate pre-heating influences the ternary composition as well as the crystalline quality of the subsequent growth. GaAs0.72P0.28 with bandgap energy of 1.76 eV has been achieved, which would be suitable for a top cell in Si tandem solar cell structures. Growth of GaP was investigated on planar GaAs as a prior study for realizing orientation patterned (OP) GaP on OP-GaAs. Threading dislocations caused by the 3.6% lattice mismatch between GaP and GaAs are suppressed by adjusting the GaCl flow, achieving a low full width at half maximum of 146 arcsec for the X-ray diffraction omega scan. Direct heteroepitaxy of GaAsP on Si aiming for achieving a GaAsP/Si dual junction solar cell is demonstrated. The inherent problem of initiating nucleation during the direct heteroepitaxy of III-V on Si by HVPE is overcome by utilizing the vapor mixing approach to grow a low-temperature GaP buffer layer on Si, followed by a GaAsP layer grown by conventional HVPE.

MODELING OF THE INDIUM GALLIUM NITRIDE TANDEM SOLAR CELL PHOTOVOLTAIC PERFORMANCES FOR CONCENTRATOR

The objective of this modeling investigation is to optimize a solar cell tandem device under the AM1.5G spectrum, based InGaN cells for concentration ratio. In this paper describes the role of the concentration photovoltaic in InGaN dual-junction solar cell. this study, the top cell is made of InGaN (1.64 eV) while the bottom cell is made of InGaN (0.94 eV).the reported for purpose was to extracted the solar cell parameters(photocurrent, open circuit voltage and efficiency) in a fairly wide range of concentration levels (1 to30 sun).Our calculation shows that the efficiency can be improved from (23.87%) for a tandem solar cell with (X=1sun) up to (25.72%) for same device solar cell with (X=30sun) for AM.1.5 illumination and room temperature.

MODELING OF THE INDIUM GALLIUM NITRIDE TANDEM SOLAR CELL PHOTOVOLTAIC PERFORMANCES FOR CONCENTRATOR

The objective of this modeling investigation is to optimize a solar cell tandem device under the AM1.5G spectrum, based InGaN cells for concentration ratio. In this paper describes the role of the concentration photovoltaic in InGaN dual-junction solar cell. this study, the top cell is made of InGaN (1.64 eV) while the bottom cell is made of InGaN (0.94 eV).the reported for purpose was to extracted the solar cell parameters(photocurrent, open circuit voltage and efficiency) in a fairly wide range of concentration levels (1 to30 sun).Our calculation shows that the efficiency can be improved from (23.87%) for a tandem solar cell with (X=1sun) up to (25.72%) for same device solar cell with (X=30sun) for AM.1.5 illumination and room temperature.

Analysis of subcell open-circuit voltages of InGaP/GaAs dual-junction solar cells fabricated using hydride vapor phase epitaxy

The current–voltage (I–V) characteristics of the individual subcells of InGaP/GaAs dual-junction (DJ) solar cells fabricated using hydride vapor phase epitaxy were investigated by electroluminescence (EL) and external quantum efficiency measurements. In particular, we found the radiative recombination efficiency of the InGaP single-junction (SJ) cell was lower by a factor of 40 than that of GaAs SJ cells because the InGaP SJ cell did not have any passivation layer at the front surface. By taking each radiative recombination efficiency into account, we accurately projected I–V curves of each subcell in the InGaP/GaAs DJ cell. By combining the projected I–V curves with short-circuit current density obtained experimentally from light I–V measurements, the open-circuit voltage (Voc) was determined to be 1339 mV for the InGaP top cell and 978 mV for the GaAs bottom cell, respectively, which were consistent with the experimentally obtained Voc values of each SJ cell.

Degradation characteristics of electron and proton irradiated InGaAsP/InGaAs dual junction solar cell

The degradation characteristics of MOCVD grown InGaAsP/InGaAs dual junction solar cells, irradiated by 1 MeV electron, 3 MeV and 10 MeV proton, have been investigated. Main electrical and optical properties of solar cell degraded seriously with the increase of irradiation fluences due to the irradiation induced defects which are acting as non-radiative recombination centers in the active layers of the solar cell. The remaining factor of Pmax is 0.67, 0.53 and 0.51 for 1 MeV electron, 10 MeV proton, and 3 MeV proton irradiation, respectively, when the displacement damage dose (DDD) is 3.16×1010 MeV/g. The degradation of external quantum efficiency (EQE) of each subcell mainly occurred in the long wavelength region, the integrated current density Jsc of InGaAsP and InGaAs subcells degraded more seriously upon 3 MeV and 10 MeV proton irradiation comparing to 1 MeV electron irradiation. The InGaAsP subcell turned out to be the current limiting unit due to the lower Jsc before and post irradiation. By applying equivalent displacement damage dose model, the relative damage coefficient for 3 MeV proton to 10 MeV proton and 1 MeV electron to 10 MeV proton have been calculated.

Monolith GaAsP/Si dual-junction solar cells grown by MBE

The growth of monolith GaAsP/Si dual-junction solar cells on Si substrates by molecular-beam epitaxy is demonstrated. The technological method for the formation of a highly doped tunnel p+/n+ junction was developed. An obvious increase in the value of the open-circuit voltage indicating the contribution of the top-junction in the total open-circuit voltage monolithic dual-junction solar cells was found.

Photoluminescence characteristics of InGaP/GaAs dual-junction solar cells under current mismatch conditions

Current mismatch is a critical factor for impairing the conversion efficiency of multi-junction solar cells. Herein, we find a visual phenomenon to distinguish whether the InGaP/GaAs dual-junction solar cell is undergoing current mismatch. It is found that the device at short circuit emits red light under the multiple-source solar simulator when the incident power of the first light source is high. Furthermore, the similar photoluminescence characteristic is also observed when two different lasers are used. These results exhibit that the photoluminescence phenomenon is a facile method to identify the current mismatch of multi-junction solar cells.

Flat concentrator photovoltaic system for automotive applications

In this paper, we present a novel design and an optical simulation of a flat concentrator photovoltaic (CPV) system for electric vehicle application. The sunlight concentration component is comprised of a planar waveguide integrated dichroic mirror-coated cone prisms and a mirror-coated lens array. Sunlight reflects firstly at the mirror-coated lens array and then strikes the cone prism of the planar waveguide. The prisms are coated by the dichroic mirrors to divide the solar spectrum into two bands. The low-energy band is transmitted and reaches the GaInAsP/GaInAs dual-junction solar cells. The mid-energy band is reflected at the prism surface and coupled inside the waveguide. The exit port of the waveguide is attached with GaInP/GaAs dual-junction solar cells. The simulation results demonstrated a maximum electricity conversion efficiency of 32.88% at the high concentration ratio. The system thickness is 35 mm, which is as thin as the conventional flat photovoltaic panel and system allow for a lateral sun-tracking mechanism. This is suitable for installation on the vehicle's roof. The results showed that the presented flat CPV system is a new approach for a highly efficient application of solar energy to the electrical vehicle.

Influence of Zn–Si donor–acceptor pair traps in invert InGaP/GaAs dual-junction solar cell by MOCVD

In In(Ga)P materials, Zn atoms diffuse into the adjacent Si doping layer at high temperatures, forming Zn–Si donor–acceptor pairs which function as non-radiation carrier recombination centers. The traps lead to decreased carrier diffusion length and separation efficiency in the space charge region of InGaP subcell, resulting in degradation of photoelectric conversion efficiency. In this paper, by adopting an InGaP p–i–n junction structure, the invert growth thin film cell was able to reach the same external quantum efficiency performance as the upright InGaP/GaAs dual-junction solar cell. The Zn doping peak was not observed at the Si doping interface layer in the electrochemical capacitance–voltage measurement. A 675 nm peak was observed at 5 and 30 K and absent in 77 K, as was resolved by low-temperature PL measurement. The peak showed a strong correlation with the Zn diffusion into adjacent Si doping InGaP layer. We speculate that the 675 nm peak represented the energy of Zn–Si donor–acceptor pair traps.

Simulation study for the current matching optimization in In0.48Ga0.52N/In0.74Ga0.26N dual junction solar cells

Abstract In this paper indium gallium nitride (InGaN) is used to design and optimize a dual junction (DJ) solar cell, which is series-connected via a tunnel diode, with a careful analysis of the current matching between the top and the bottom sub-cells. In particular, a bandgap combination of 1.76eV/1.13eV for an In0.48Ga0.52N/In0.74Ga0.26N structure is adopted and several numerical simulation results are presented. The doping concentration and the base thickness of each sub-cell are considered as fitting parameters in order to determine an accurate current matching condition. The In0.48Ga0.52N-based n++/p++ tunnel junction behavior is also taken into account. A maximum short circuit current density of 19.543 mA/cm2 is obtained for a 1 μm-thick base in both the sub-cells, and a p/n doping ratio of 5 × 1018 cm−3/5 × 1015 cm−3 and 1.9 × 1019 cm−3/1.9 × 1016 cm−3 for the top and the bottom cell, respectively. The optimized DJ solar cell exhibits an open circuit voltage of 1.713 V, a fill factor of 82.49%, and a conversion efficiency of 28.78%. The external quantum efficiency and the current (power) density-voltage characteristics of different devices are investigated in detail.

Analytical Modeling of Dual-Junction Tandem Solar Cells Based on an InGaP/GaAs Heterojunction Stacked on a Ge Substrate

An analytical model is used to describe the electrical characteristics of a dual-junction tandem solar cell performing with a conversion efficiency of 32.56% under air mass 1.5 global (AM1.5G) spectrum. The tandem structure consists of a thin heterojunction top cell made of indium gallium phosphide (InGaP) on gallium arsenide (GaAs), mechanically stacked on a relatively thick germanium (Ge) substrate, which acts as bottom cell. In order to obtain the best performance of such a structure, we simulate for both the upper and lower sub-cell the current density–voltage, power density–voltage, and spectral response behaviors, taking into account the doping-dependent transport parameters and a wide range of minority carrier surface recombination velocities. For the proposed tandem cell, our calculations predict optimal photovoltaic parameters, namely the short-circuit current density (Jsc), open-circuit voltage (Voc), maximum power density (Pmax), and fill factor (FF) are Jsc = 28.25 mA/cm2, Voc = 1.24 V, Pmax = 31.64 mW/cm2, and FF = 89.95%, respectively. The present study could prove useful in supporting the design of high efficiency dual junction structures by investigating the role of different materials and physical parameters.

Performance comparison of III\u2013V//Si and III\u2013V//InGaAs multi-junction solar cells fabricated by the combination of mechanical stacking and wire bonding

The integration of III–V and Si multi-junction solar cells as photovoltaic devices has been studied in order to achieve high photovoltaic conversion efficiency. However, large differences in the coefficients of thermal expansion and the lattice parameters of GaAs, Si, and InGaAs have made it difficult to obtain high-efficiency solar cells grown as epilayers on Si and InP substrates. In this paper, two types of devices, including GaInP/GaAs stacked on Si (GaInP/GaAs//Si) and GaInP/GaAs stacked on InGaAs (GaInP/GaAs//InGaAs), are fabricated via mechanical stacking and wire bonding technologies. Mechanically stacked GaInP/GaAs//Si and GaInP/GaAs//InGaAs triple-junction solar cells are prepared via glue bonding. Current-voltage measurements of the two samples are made at room temperature. The short-circuit current densities of the GaInP/GaAs//Si and GaInP/GaAs//InGaAs solar cells are 13.37 and 13.66 mA/cm2, while the open-circuit voltages of these two samples are measured to be 2.71 and 2.52 V, respectively. After bonding the GaInP/GaAs dual-junction with the Si and InGaAs solar cells, the conversion efficiency is relatively improved by 32.6% and 30.9%, respectively, compared to the efficiency of the GaInP/GaAs dual-junction solar cell alone. This study demonstrates the high potential of combining mechanical stacked with wire bonding and ITO films to achieve high conversion efficiency in solar cells with three or more junctions.