GaInP Top Cell Research Articles

Sheet Resistance Optimization in (Al)GaInP Solar Cells for Concentrator Quadruple–Junction Solar Cells

The reduction of the series resistance in multi‐junction solar cells is of high importance for attaining peak efficiencies in concentrator photovoltaics. This study showcases strategies to reduce the sheet resistance of the uppermost subcell of a direct wafer bonded four–junction devices, since it contributes significantly to the series resistance. Therefore, electron mobilities in n–type AlGaInP, lattice matched to GaAs, are investigated across bandgap energies between 1.9 and 2.1 eV and various doping concentrations. The sheet resistances for AlGaInP rear heterojunction cells are determined for the integration in a two terminal four‐junction solar cell. The rear heterojunction cell architecture effectively addresses the sheet resistance optimization because it features a thick n‐type doped absorption layer. The sheet resistance of our current world record quadruple‐junction solar cell with 47.6% efficiency under the 665‐fold concentrated AM1.5d spectrum is 550 Ω sq−1. Herein, it is shown that optimizing the n‐absorption layer in the 1.90 eV GaInP top cell can reduce the sheet resistance to 250 Ω sq−1 without deteriorating the short–circuit current density and current matching. This reduction corresponds to a 5 mΩ cm2 improvement in specific series resistance, which would elevate the efficiency of this device to 48.2%.

TOPcon route with quantum wells in GaInP/Si dual junction cell for efficiency enhancement

The GaInP/Si dual junction solar cell with Quantum Well and TOPCon technology has achieved 41.91 % efficiency in the simulation model. Quantum wells are proven to enhance the short circuit current without any significant degradation of open circuit voltage. The voltage preservation measure (for minimum reduction in open circuit voltage) is applied in design of Quantum well solar cell with the improvement in short circuit current, therefore the overall efficiency of dual junction cell is enhanced. In this work, the GaInP/Si dual junction solar cell is proposed by incorporating the InP quantum wells in the p-i-n region of GaInP top cell. Also, the TOPCon technology is applied at the rear side of the bottom c-Si solar cell. The quantum well increases the absorption of sub-bandgap photon energy. The buffer layer reduces the misfits between the lattice mismatched layers and tunnel oxide provides excellent passivation mechanism to increase the open circuit voltage. The ultrathin oxide layer provides extremely high electric field as described by the MIS tunneling theory. The electron and hole bound state energy and wavefunctions provides “miniband” formation and charge carrier trapping. The formation of type-A band structure in quantum well region and excellent electron mobility results in enhanced carrier transport. The GaInP/Si integrated model achieves efficiency of 33.30 % when the quantum wells are incorporated in the top cell. When the Combination of both QWs (in top cell) and TOPCon technology (in bottom cell) is applied, the model achieves 41.95 % efficiency. This model provides an excellent route toward achieving the 45 % efficiency limit of III-V/Si dual junction 2-terminal solar cell. The industry standard Silvaco TCAD platform is used for the calculation of the performance characteristics in AM1.5G environmental condition.

Triple-junction solar cells with 39.5% terrestrial and 34.2% space efficiency enabled by thick quantum well superlattices

<h2>Summary</h2> Multijunction solar cell design is guided by both the theoretical optimal bandgap combination as well as the realistic limitations to materials with these bandgaps. For instance, triple-junction III-V multijunction solar cells commonly use GaAs as a middle cell because of its near-perfect material quality, despite its bandgap being higher than optimal for the global spectrum. Here, we modify the middle cell bandgap using thick GaInAs/GaAsP strain-balanced quantum well (QW) solar cells with excellent voltage and absorption. These high-performance QWs are incorporated into a triple-junction inverted metamorphic multijunction device consisting of a GaInP top cell, GaInAs/GaAsP QW middle cell, and lattice-mismatched GaInAs bottom cell, each of which has been highly optimized. We demonstrate triple-junction efficiencies of 39.5% and 34.2% under the AM1.5 global and AM0 space spectra, respectively, and the global efficiency is higher than previous record six-junction devices.

Dopant Diffusion Control for Improved Tandem Cells Grown by D-HVPE

GaInP top cell current-density presently limits the performance of HVPE-grown two-junction devices, in large part due to unwanted dopant diffusion. Here, we institute mitigation strategies to lower the diffusion of dopants from both the front contact and back surface field. Successful application of these strategies resulted in a short-circuit current density of 12.1 mA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> in a GaInP/GaAs cell, an improvement of 0.9 mA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> over our previous best cell. The reduced Se diffusion results in a thinner unpassivated emitter, which can lead to higher series resistance. Despite the increased resistance we obtained an efficiency increase from 23.7% to 24.8%.

Energy Yield Analysis of Multiterminal Si-Based Tandem Solar Cells

We present a model for a yield analysis of tandem devices consisting of Si bottom cells with III-V top cells. It accounts for the spectral properties of the subcells as well as their reduced operating temperature due to increased efficiency and luminescent coupling. Inputs are the experimental I–V and QE data of the subcells (e.g., available from laboratory prototypes) and the irradiance-dependent module temperature of the bottom cell. We apply the model to compare two types of tandem cells, GaInP and GaAs top cells on Si bottom cells. The impact of the temperature model, compared to a constant temperature, shows a relative change in energy yield of up to 2.7%rel. Including luminescent coupling for GaAs/Si devices with two terminals, increases the energy yield by 34.0%rel. This is still 34.2%rel less energy yielded than for GaInP/Si two-terminal devices. The performance of the GaInP/Si devices can be improved by 5.8%rel using three-terminal devices with back-contacted bottom cells instead of a two-terminal configuration under the assumption of a cell string with voltage matching of one top cell with two bottom cells. For GaInP/Si, the three-terminal device performs similarly to the four-terminal device, enabling the integration of monolithic tandem cells into modules at comparably high efficiencies.

Temperature-dependent photoluminescence processes of GaInP top cell irradiated with 11.5 MeV and 1.0 MeV electrons

The effects of 11.5 MeV electrons irradiation on the GaInP top cell of GaInP/GaAs/Ge triple-junction solar cells have been investigated by temperature-dependent photoluminescence (PL) measurements. The thermal quenching of PL intensity is observed in the temperature range of 10 K–270 K, attributing to the nonradiative recombination centers H2 (Ev + 0.55 eV) hole trap and H3 (Ev + 0.76 eV) hole trap. A slight negative thermal quenching (NTQ) of PL intensity exists at nearly 300 K and could be associated with the 0.18 eV intermediate states. The temperature-dependent photoluminescence process of GaInP top cell irradiated with 11.5 MeV electrons differs with that irradiated with 1.0 MeV electrons.

Effect of interfacial AsH3 surge treatment on GaInP/GaAs dual-junction solar cells grown by metal–organic vapor phase epitaxy

The effect of a modified PH3-to-AsH3 gas switching sequence with an AsH3 surge treatment on GaInP/GaAs dual-junction solar cells was studied. With AsH3 surge treatment, both the material quality with an absence of defects and device performance was preserved, but without it, deterioration in both of these characteristics was observed, which originated in the As/P interface. It was found that defects with an inhomogeneous III–metal composition were formed at the interface and developed into a V-shaped dislocation which penetrated the GaInP top cell. The results suggest that sufficient arsenic supply is necessary prior to As-based material growth on GaInP.

Electron-induced degradation of J-V characteristics of GaInP top cell and GaAs middle cell by electroluminescence measurements

Electroluminescence (EL) measurements were carried out to investigate the irradiation effects of 1.0 MeV electrons on the current density-voltage (J-V) characteristics of the GaInP top cell and GaAs middle cell of GaInP/GaAs/Ge triple-junction solar cells at injection current densities ranging from 2.5 mA/cm2 to 30 mA/cm2. By utilizing the optoelectronic reciprocity relation between the EL and external quantum efficiency, the dark J-V characteristics of the two subcells, as well as the short circuit current density and the open circuit voltage, were derived. It is shown that the short circuit current density and the open circuit voltage of the top cell and the middle cell both degrade with the increasing fluence, but that of the middle cell degrades more than the top cell at the same fluence. Meanwhile, the current-limiting cell changes from GaInP top cell to the GaAs middle cell. The GaAs middle cell contributes to more loss in voltage of the 3 J solar cell.

Photoluminescence Analysis of Electron Damage for Minority Carrier Diffusion Length in GaInP/GaAs/Ge Triple-Junction Solar Cells**Supported by the National Natural Science Foundation of China under Grant Nos 11675020, 11375028, 11075018 and 10675023.

Photoluminescence (PL) measurements are carried out to investigate the degradation of GaInP top cell and GaAs middle cell for GaInP/GaAs/Ge triple-junction solar cells irradiated with 1.0, 1.8 and 11.5MeV electrons with fluences ranging up to 3 × 1015, 1 × 1015 and 3 × 1014 cm−2, respectively. The degradation rates of PL intensity increase with the electron fluence and energy. Furthermore, the damage coefficient of minority carrier diffusion length is estimated by the PL radiative efficiency. The damage coefficient increases with the electron energy. The relation of damage coefficient to electron energy is discussed with the non-ionizing energy loss (NIEL), which shows a quadratic dependence between damage coefficient and NIEL.

3.0 MeV proton-irradiation induced non-radiative recombination center in the GaAs middle cell and the GaInP top cell of triple-junction solar cells

3.0 MeV proton-irradiation effects on the GaAs middle cell and the GaInP top cell of n+-p GaInP/GaAs/Ge triple-junction (3J) solar cells have been analyzed using temperature-dependent photoluminescence (PL) technique. The E5 (Ec - 0.96 eV) electron trap in the GaAs middle cell, the H2 (Ev + 0.55 eV) hole trap in the GaInP top cell are identified as the proton irradiation-induced non-radiative recombination centers, respectively, causing the performance degradation of the triple-junction solar cells. The GaAs middle cell is less resistant to proton irradiation than the GaInP top cell.

Negative thermal quenching of the defects in GaInP top cell with temperature-dependent photoluminescence analysis

Abstract Temperature-dependent photoluminescence (PL) measurements were carried out to investigate the irradiation effects of 1.0 MeV electrons on the n+- p GaInP top cell of GaInP/GaAs/Ge triple-junction solar cells in the 10–300 K temperature range. The PL intensities plotted against inverse temperature in an Arrhenius plot shows a thermal quenching behavior from 10 K to 140 K and an unusual negative thermal quenching (NTQ) behavior from 150 K to 300 K. The appearance of the PL thermal quenching with increasing temperature confirms that there is a nonradiative recombination center, i.e., the H2 hole trap located at Ev + 0.55 eV, in the cell after electron irradiation. The PL negative thermal quenching behavior may tentatively be attributed to the intermediate states at an energy level of 0.05 eV within the band gap in GaInP top cell.

Realization of GaInP/Si Dual-Junction Solar Cells With 29.8% 1-Sun Efficiency

Combining a Si solar cell with a high-bandgap top cell reduces the thermalization losses in the short wavelength and enables theoretical 1-sun efficiencies far over 30%. We have investigated the fabrication and optimization of Si-based tandem solar cells with 1.8-eV rear-heterojunction GaInP top cells. The III–V and Si heterojunction subcells were fabricated separately and joined by mechanical stacking using electrically insulating optically transparent interlayers. Our GaInP/Si dual-junction solar cells have achieved a certified cumulative 1-sun efficiency of 29.8% ± 0.6% (AM1.5g) in four-terminal operation conditions, which exceeds the record 1-sun efficiencies achieved with both III–V and Si single-junction solar cells. The effect of luminescent coupling between the subcells has been investigated, and optical losses in the solar cell structure have been addressed.

Effects of 1.0–11.5 MeV Electron Irradiation on GaInP/GaAs/Ge Triple-junction Solar Cells for Space Applications

GaInP/GaAs/Ge triple-junction solar cells are irradiated with 1.0, 1.8, and 11.5 MeV electrons with fluence ranging up to 3 × 1015, 3 × 1015, and 3 × 1014 cm−2, respectively. Their performance degradation effects are analyzed by using current-voltage characteristics, spectral response measurements, and electron irradiation-induced displacements. The degradation rates of the maximum power and the spectral response of the solar cells increase with the electron fluence, and also increase with the increasing electron energy. It is observed that the spectral response of the GaAs middle cell degrades more significantly than that of the GaInP top cell.

Electroluminescence analysis of injection-enhanced annealing of electron irradiation-induced defects in GaInP top cells for triple-junction solar cells

Direct injection-enhanced annealing of defects in a GaInP top cell for GaInP/GaAs/Ge triple-junction solar cells irradiated with 1.8MeV electrons with a fluence of 1×1015 cm−2 has been observed and analyzed using electroluminescence (EL) spectra. Minority-carrier injection under forward bias conditions is observed to enhance defect annealing in the GaInP top cell, and recovery of the EL intensity of the GaInP top cell was observed even at room temperature. Moreover, the injection-enhanced defect annealing rates obey a simple Arrhenius law; therefore, the annealing activation energy was determined and is equal to 0.51eV. Lastly, the H2 defect has been identified as the primary non-radiative recombination center based on a comparison of the annealing activation energies.

Effects of leakage current on the short circuit current in the dual-junction solar cells

The characteristics of short circuit current (I\(_\mathrm{sc})\) in dual-junction GaInP/GaAs solar cells have been investigated, and the experimental results show that the photo current of GaInP top cell is higher than that of GaAs bottom cell and the I\(_\mathrm{sc}\) of the device is usually not limited by GaAs bottom cell if a leakage current occurs. The current versus voltage (I–V) curves of the solar cell were simulated with subcells based on single diode model and the I\(_\mathrm{sc}\) shows a dependence on the leaky subcells, i.e., the I\(_\mathrm{sc}\) is between the photo current of GaAs and that of GaInP subcells in the case of a leaky GaAs subcell, it is equal to the photo current of GaAs subcell in the case of a leaky GaInP subcell, and it is lower than the photo current of GaInP subcell when both GaAs and GaInP subcells are leaky.

GaInP/GaAs Tandem Solar Cells With InGaAs/GaAsP Multiple Quantum Wells

Lattice-matched multiple quantum wells (MQWs) consisting of In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> As wells with very thin GaAs <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.2</sub> P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.8</sub> barriers have been incorporated into a GaInP/GaAs tandem solar cell. InGaAs/GaAsP MQWs increase the short-circuit current of the GaAs cell by extending the absorption range, with minimal impact on an open-circuit voltage, thus alleviating current matching restrictions placed by the GaAs cell on multijunction solar cells. MQWs with very thin, tensile strained, high phosphorus content GaAsP barriers allow tunneling to dominate carrier transport across the MQWs and balance the compressive strain of the InGaAs wells such that material quality remains high for subsequent top cell growth. We show that the addition of the QW layers enhances the GaAs cell, does not degrade the performance of the GaInP top cell, and leads to potential efficiency enhancements.

Surexpression de l’IL-31 dans une forme sporadique de lichen amyloïde : un lien avec le prurit ?

Radiative recombination of carriers in two kinds of GaxIn1−xP/GaAs double-junction tandem solar cell structures was investigated by using room-temperature electroluminescence (EL) and photoluminescence (PL) techniques. Efficient radiative recombination was observed simultaneously in the top and the bottom subcells in both the samples. By studying the behavior of EL and PL spectra, the radiative recombination intensity ΦEL was demonstrated to be reliant on the material-dependent radiative recombination coefficient, base layer doping concentration and thickness. Furthermore, dependence of ΦEL on substrate misorientation in both the subcells was also evidenced, which was explained in terms of the growth-induced variations in microstructure for the GaInP top cell and in potential barrier profile across the p–n junction for the GaAs bottom cell. Based on these observations, the radiative recombination in the two base layers of the subcells was demonstrated to be the major carrier loss mechanism in the GaxIn1−xP/GaAs double-junction tandem photovoltaic devices and should be suppressed.

Influence of PH3 exposure on silicon substrate morphology in the MOVPE growth of III–V on silicon multijunction solar cells

Dual-junction solar cells formed by a GaAsP or GaInP top cell and a silicon bottom cell seem to be attractive candidates to materialize the long sought-for integration of III–V materials on silicon for photovoltaic applications. One of the first issues to be considered in the development of this structure will be the strategy to create the silicon emitter of the bottom subcell. In this study, we explore the possibility of forming the silicon emitter by phosphorus diffusion (i.e. exposing the wafer to PH3 in a MOVPE reactor) and still obtain good surface morphologies to achieve a successful III–V heteroepitaxy as occurs in conventional III–V on germanium solar cell technology. Consequently, we explore the parameter space (PH3 partial pressure, time and temperature) that is needed to create optimized emitter designs and assess the impact of such treatments on surface morphology using atomic force microscopy. Although a strong degradation of surface morphology caused by prolonged exposure of silicon to PH3 is corroborated, it is also shown that subsequent anneals under H2 can recover silicon surface morphology and minimize its RMS roughness and the presence of pits and spikes.

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.

Understanding phosphorus diffusion into silicon in a MOVPE environment for III–V on silicon solar cells

Dual-junction solar cells formed by a GaAsP or GaInP top cell and a silicon bottom cell seem to be attractive candidates to materialize the long sought-for integration of III–V materials on silicon for photovoltaic applications. When manufacturing a multi-junction solar cell on silicon, one of the first processes to be addressed is the development of the bottom subcell and, in particular, the formation of its emitter. In this study, we analyze, both experimentally and by simulations, the formation of the emitter as a result of phosphorus diffusion that takes place during the first stages of the epitaxial growth of the solar cell. Different conditions for the Metal-Organic Vapor Phase Epitaxy (MOVPE) process have been evaluated to understand the impact of each parameter, namely, temperature, phosphine partial pressure, time exposure and memory effects in the final diffusion profiles obtained. A model based on SSupremIV process simulator has been developed and validated against experimental profiles measured by ECV and SIMS to calculate P diffusion profiles in silicon formed in a MOVPE environment taking in consideration all these factors.