Dual-junction Solar Cells Research Articles

Optimal performance of silicon nanowire solar cells under low sunlight concentration and their integration as bottom cells in III–V multijunction systems

Nanostructured silicon solar cells are designed to minimize costs through reduced material usage while enhancing power conversion efficiency via superior light trapping and shorter charge separation distances compared to traditional planar cells. This study identifies the optimal conditions for nanoimprinted silicon nanowire (SiNW) solar cells to achieve maximum efficiency under low sunlight concentration and evaluates their performance as bottom cells in III–V multijunction solar cell systems. The findings indicate that the SiNW solar cell reaches its peak performance at a concentration factor of 7.5 suns and a temperature of 40°C or lower. Specifically, the absolute conversion efficiency under these conditions is 1.05% higher than that under unconcentrated light. Compared to a planar silicon solar cell under identical conditions, the SiNW solar cell exhibits a 3.75% increase in conversion efficiency. Additionally, the SiNW single-junction solar cell, when integrated in series with a commercial lattice-matched InGaP/GaAs dual-junction solar cell, was tested under unconcentrated sunlight, specifically at one-sun, global air mass 1.5 condition, to assess its viability in one-sun multi-junction solar cell applications. The results suggest that a III–V upper subcell with a smaller active area than that of the SiNW subcell is optimal for maximizing current production, which is favorable to the cost reduction of the device. This hybrid configuration is particularly advantageous for terrestrial applications, such as electric vehicles, which demand lightweight, high-performance multijunction solar cell devices. Although the weight reduction of the characterized SiNW solar cell with a full silicon substrate compared to its planar solar cell counterpart is 1.8%, recommendations to increase this reduction to as much as 64.5% are discussed to conclude this paper.

Design and optimization of a high efficiency CdTe–FeSi2 based double-junction two-terminal tandem solar cell

This article theoretically demonstrates an enormously efficient CdTe–FeSi2 based dual-junction tandem solar cell accompanied by slender semiconductor layers. The peak efficiency of the device has been ensured through the optimization of its various attributes of window, CdTe (bandgap 1.5 eV) top absorber, FeSi2 (bandgap 0.87 eV) bottom absorber and back surface layers. Additionally, the impacts of thickness, doping and the level of defects in different window, base and rear surface layers have been examined to observe how different layers affect the solar cell's performance. The optimized n-CdS/p-CdTe/p+-MoS2--n-CdS/p-FeSi2/p+-Cu2SnS3 dual-junction tandem solar device displays an efficiency of 43.9% with a voltage at no load, VOC of 1.928 V, current density under a closed circuit, JSC of 25.34 mA/cm2, and fill factor of 89.88%, respectively. These results disclose the high potential of the suggested solar cell based on CdTe and FeSi2 compounds.

Exploring the impact of defect energy levels in CdTe/Si dual-junction solar cells using wxAMPS

A numerical analysis of a CdTe/Si dual-junction solar cell in terms of defect density introduced at various defect energy levels in the absorber layer is provided. The impact of defect concentration is analyzed against the thickness of the CdTe layer, and variation of the top and bottom cell bandgaps is studied. The results show that CdTe thin film with defects density between 1014 and 1015 cm−3 is acceptable for the top cell of the designed dual-junction solar cell. The variations of the defect concentrations against the thickness of the CdTe layer indicate that the open circuit voltage, short circuit current density, and efficiency (ƞ) are more affected by the defect density at higher CdTe thickness. In contrast, the Fill factor is mainly affected by the defect density, regardless of the thin film’s thickness. An acceptable defect density of up to 1015 cm−3 at a CdTe thickness of 300 nm was obtained from this work. The bandgap variation shows optimal results for a CdTe with bandgaps ranging from 1.45 to 1.7 eV in tandem with a Si bandgap of about 1.1 eV. This study highlights the significance of tailoring defect density at different energy levels to realize viable CdTe/Si dual junction tandem solar cells. It also demonstrates how the impact of defect concentration changes with the thickness of the solar cell absorber layer.

Monolithic Two-Terminal Perovskite/Perovskite/Silicon Triple-Junction Solar Cells with Open Circuit Voltage >2.8 V.

The efficiency of perovskite/silicon tandem solar cells has exceeded the previous record for III-V-based dual-junction solar cells. This shows the high potential of perovskite solar cells in multi-junction applications. Perovskite/perovskite/silicon triple-junction solar cells are now the next step to achieve efficient and low-cost multi-junction solar cells with an efficiency potential even higher than that for dual-junction solar cells. Here we present a perovskite/perovskite/silicon triple-junction solar cell with an open circuit voltage of >2.8 V, which is the record value reported for this structure so far. This is achieved through employing a gas quenching method for deposition of the top perovskite layer as well as optimization of interlayers between perovskite subcells. Moreover, for the measurement of our triple-junction solar cells, precise measurement procedures are implemented to ensure the reliability and accuracy of the reported values.

Improvement Efficiency of Solar Cells Using III-V Dual Junction: InGap/GaAs

Renewable energy is a very minor percentage of energy consumed in the world. Fossil fuels still dominate despite their drawbacks (degradation of the environment). Renewable energy is not yet cost competitive with fossil fuels. The conversion of energy from renewable sources, especially for inexhaustible and clean energy sources (solar cells), must be efficient to be viable for large scale use. Single junction cells (SJC) have a theoretical efficiency limit of 33.7%, called Shockley-Queisser limit (SQ). Because the cost of electricity produced from solar cells depends on their efficiency, improving their conversion efficiency is a key way to make them cost-competitive. The two most important efficiency losses in SJC are the inability to convert photons with energies below the band gap energy (Eg) into electricity and the thermalization of photon energies exceeding Eg. Dual Junction Solar Cells (DJSC) was proposed to avoid the efficiency losses and to overcome the SQ limit. Our simulation model, presented in a previous work, was used to calculate solar cells efficiency and to plot the current-voltage (I-V) characteristics and the power-voltage (P-V) characteristics curves. Our simulation results show that high conversion efficiencies can be achieved by DJSC, more than 43.5%.

Simulation study of the tunnel junction position effect on the parameters of the InxGa1-xN dual junction solar cell

The present work presents a SILVACO-Atlas numerical simulation to investigate the effect of the tunnel junction position on the performance of InxGa1−xN double-junction solar cells under AM1.5 solar illumination. The proposed cell is composed of two PN sub-cells, an upper sub-cell in In0.1Ga0.9N and a lower sub-cell in In0.4Ga0.6N for the p-type and In0.2Ga0.8N for the n-type, connected by a tunnel junction in In0.4Ga0.6N. The cell offers a remarkable open-circuit voltage value of about 3.9 V and a good fill shape value of about 93. A cell with a small overall thickness can offer better transfer efficiency than a cell with a large thickness if the tunnel junction position is carefully chosen. The proposed cell can achieve a transfer efficiency of around 18% with an overall thickness of 0.652 μm.

Improved radiation resistance of flexible GaInP/GaAs dual junction solar cell by optimizing GaAs subcell i-layer

The radiation effects of flexible GaInP/GaAs solar cells under 1 MeV electron irradiation have been studied. GaAs subcell intrinsic layer thickness showed remarkable effects on the solar cell radiation resistance. Based on the integrated current density of subcells, GaAs is determined as the current-limiting subcell before and after irradiation regardless to the i-layer thickness, while GaInP subcell exhibits superior radiation resistance. For 1.5 × 1015 e/cm2 irradiation fluence, the remaining factors of maximum output power are 71.94%, 82.53%, and 82.38%, for GaInP/GaAs solar cells with 0, 0.6 μm, 1.0 μm thick i-layer, respectively. EQE spectra of GaAs subcell degraded more in long-wavelength area, due to the higher defect concentration in the base layer. The flexible GaInP/GaAs dual junction solar cell with 0.6 μm thick i-layer sample exhibited an initial conversion efficiency of 23.79%, and the remaining factor is 82.51% after 1.5 × 1015 e/cm2 fluence electron irradiation.

Bandgap engineered 1.48 eV GaAs0.95P0.05 solar cell with enhanced efficiency using double BSF layer

One of the most important criteria to design more than 30% efficient III–V compound/Si based dual junction solar cell is that we must design atleast 20% efficient III–V compound material top cell. In this regard, we designed a bandgap engineered GaAs0.95P0.05 single junction solar cell with reduced bandgap of (E g ) = 1.48 eV. Reducing the bandgap from 1.72 eV to 1.48 eV for GaAs0.95P0.05 cell leads to generate higher short circuit current, while having the tradeoff with the open circuit voltage. Due to small change in lattice constant of GaAs0.95P0.05 cell, some recombination is observed near the junction area. Although the minimal degradation is observed in open circuit voltage, the higher short circuit current drives the overall efficiency of the GaAs0.95P0.05 single junction solar cell. The designed solar cell provides an extended internal absorption for longer wavelength of spectrum. The high electron mobility of 8500 cm2 V–S−1 was observed with very high electron to hole mobility ratio of 21.25. The optimization of the cell is done using two back surface field layers (AlInP and AlGaInP) of higher bandgap material. The high short circuit current density of J SC = 25.93 mA cm−2 with V OC = 1.1635 V achieved by the designed cell with the highest efficiency of η = 25%. The solar cell is irradiated under 1-Sun solar irradiation in the AM1.5 G environment providing 1000 W m−2 of power spectral density. The External and Internal Quantum efficiency of more than 95% is achieved by the designed solar cell.

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.

Analytical Model of InP QWs for Efficiency Improvement in GaInP/Si Dual Junction Solar Cell

Quantum wells (QWs) are proven to enhance the short circuit current and voltage preservation measures help in efficiency enhancement with little degradation of open circuit voltage . Herein, an integrated GaInP/Si dual junction solar cell is proposed by incorporating the QWs in the top cell and carrier‐selective passivated contact at the bottom cell of the design. The QW increases the photon absorption of sub‐bandgap energies, buffer layer reduces the misfits between the lattice mismatched layers, and passivation mechanism improves the overall efficiency. Increasing the number of QWs increases the depletion width of QW region. This reduces the carrier lifetime () and increases the recombinations in the QW region. It results in the reduction in passivation quality and, therefore, reduces the open circuit voltage (). QW strain balancing and measures to reduce the threading dislocations has been considered. Also, the wide bandgap GaInP tunnel junction along with highly doped GaAs tunnel junction has been analyzed to observe the parasitic effect. The GaInP/Si‐integrated model achieves efficiency of 33.39% when the QWs are incorporated in the top cell. The effect of wide bandgap tunnel junction is also evaluated using GaInP tunnel junction.

Modeling Arc less Ingap/Gaas Double Junction Solar Cell with Tunneling Junction and Bsf Layer

The present study addresses the structure of InGaP/GaAs dual-junction (DJ) solar cells by introducing new buffer and back surface field (BSF) layers as well as selecting the appropriate material for the tunnel junction. Different performance parameters including open-circuit voltage (𝑉oc) short-circuit current density (𝐽𝑆𝐶), fill factor (𝐹𝐹), and solar cell efficiency (𝜂) were proposed and extracted for comparison with literature results. Then, I-V characteristic curves for the model were represented in graphs. The mentioned parameters, i.e. open-circuit voltage 𝑉𝑂𝐶, short-circuit current density 𝐽𝑆𝐶, fill factor 𝐹𝐹, and solar cell efficiency 𝜂 were, respectively, obtained as 18.50 𝑚𝐴/𝑐𝑚2, 2.862 V, 87/32 percent and 46.23 percent (1sun) under AM1.5G spectrum, which indicates the improvement achieved in this study.

Optimizing efficiency of InGaP/GaAs dual-junction solar cells with double tunnel junction and bottom back surface field layers

Dual-junction solar cells have permitted to augment markedly efficiency of solar energy harvesting. This is because they involve a combination of III-V semiconductor materials with different band gaps which enables for better absorbance of the solar spectrum and consequently higher efficiency. In these last years, intensive research has been dedicated to develop reliable methods for performing structural optimization of these devices. This work proposes a new numerical procedure in order to achieve optimal design of a dual junction solar cell made of InGaP/GaAs tandem combination. This particular structure relies on the InGaP single junction solar cell, which is used as a front stack, and a back surface field. Optimization was conducted sequentially through post processing data results generated from large parametric simulations performed by using the 2D SILVACO-ATLAS software. The procedure encompasses using either a quadratic response surface model or an artificial neural network model at each stage of the optimization process to determine the actual optimal design of the solar cell. The obtained final optimal design has been shown to yield, under the AM1.5 spectrum, an efficiency of 35.15% at temperature 20°C which is higher than that of previous known results from literature.

High-Efficiency p-n Homojunction Perovskite and CIGS Tandem Solar Cell

Efficiency has been known to be one of the most important factors in a solar cell. This article presents the results of a simulation performed on a perovskite/CIGS dual-junction solar cell. In this report, first, a top solar cell consisting of a perovskite absorber layer is simulated using the pn-junction; the separation and transfer of carriers in this structure are done by the internal electric field. The pn-junction has a discharge area smaller than the pin-junction, which increases carrier recombination and reduces optical losses. The perovskite band gap of 1.9 eV is considered, and the efficiency is 21.65% using the Au electrode. Then, the bottom solar cell is fabricated with a CIGS absorbent layer with a 1.4 eV band gap and an efficiency of 11.46%. After simulating and evaluating the performance of the top and bottom solar cells independently, both cells were simulated and examined for the dual-junction state. Since the perovskite and CIGS band gaps are both adjustable, these two materials can act as a proper partner for an absorbent layer in a dual-junction solar cell. In this structure, instead of the usual connection of p-i-n and n-i-p perovskite, n-type and p-type homojunction perovskite connection is used, in which the transfer and separation of carriers are done by an internal electric field. Due to the fact that in this structure, the discharge area is smaller, the recombination of carriers is increased, and the light losses are reduced, which will increase the absorption and efficiency of the cell. The results show that in the tandem design, we encounter an increase in Voc (2.25 V), thus increasing the efficiency of the solar cell (30.71%).

High Electric Field Sensing in Ultrathin SiO₂ and Tunnel Region to Enhance GaInP/Si Dual Junction Solar Cell Performance

The Si material is widely used by the manufacturers for sensing applications, because of its abundance. Better carrier sensing capability provide high performance. Solar cell is a sensor, which can sense the sun spectrum to convert it into electrical energy. This paper presents enhancement of passivation quality of GaInP/Si dual junction solar cell by enhancing the carrier transport through tunnel oxide. Reducing the SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> thickness increases the transport channel, thereby increasing the electric filed. This enhanced electric field accelerates the carrier transport in the passivation layer, and ultimately the passivation quality improves due to enhanced carries. The high electric field sensing accelerates the majority carriers towards the rear surface. Here, the improvement of the passivation quality is achieved via scaling down the oxide thickness as explained in the MIS tunneling theory. Reduction in oxide thickness provide more transport channels for the carriers, hence improves the tunneling process. Improved carrier sensing in 300nm-1100nm wavelength range, can progress towards the thermodynamic limit of open circuit voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\textit {oc}}$ </tex-math></inline-formula> ). Also, we have used a wide-bandgap tunnel junction to electrically connect two cells, to see the effect on spectrum loss. The thickness and doping concentration of the tunnel junction plays very important role in tunneling process. Sharp edges and fast tunneling of the tunnel junction is the key element in proper current matching process. Numerical analysis of tunnel oxide thickness variation and wide-bandgap tunnel junction is done to obtain the optimum efficiency of 36.22% under 1-Sun concentration.

Dual Junction GaInP/GaAs Solar Cell with Enhanced Efficiency Using Type‐A InP Quantum Wells

Multijunction solar cells (SCs) have excellent potential to achieve higher efficiency for increased sun concentration. The two‐step photon absorption in the quantum wells (QWs) can further enhance the performance of the solar cell. A GaInP/GaAs dual junction solar cell is proposed with InP QWs. The type‐A InP QWs are inserted in the intrinsic region of the top cell because in the top cell, short‐circuit current governs the overall cell current. The voltage preservation is applied by careful structuring of the p–i–n region at the top cell. The sub‐band photon absorption enhances the external and internal quantum efficiency (QE) of the top cell, and both cells have above 90% QEs. The peak efficiencies of 44.09% under 1 sun and 48.18% under 1000 sun concentrations are achieved, and the performance is compared with the available experimental and simulated data.

Inverted metamorphic InGaAsP/InGaAs dual-junction solar cells towards full solar spectrum harvesting

An InGaAsP (1.04 eV)/InGaAs (0.54 eV) dual-junction solar cell, monolithically grown in an inverted configuration on an InP substrate, has been demonstrated.

Growth Optimization of InGaP/GaAs Dual Junction Solar Cells With Quantum Wells and a Distributed Bragg Reflector

Growth Optimization of InGaP/GaAs Dual Junction Solar Cells With Quantum Wells and a Distributed Bragg Reflector

Simulation and performance optimization of GaAs/GaSb tandem solar cell

Multi-junction solar cells provide the highest efficiencies. Intense research activity is being held with the aim to increase the actual performance reached by these cells. Harvesting most of the solar spectrum and finding the optimum design variables in terms of structural parameters and carrier concentrations are the main topics being investigated by solar developers. The GaAs/GaSb based dualjunction solar cell was found suitable for the best absorption of solar spectrum. In this work, an optimization approach was applied to fix the optimal parameters of the top base layer of this structure that provide the maximum efficiency. To achieve this, a series of numerical simulations were carried out by means of Silvaco ATLAS software under standard AM1.5G spectrum where thicknesses and doping levels of the top base layer were varied. The obtained optimal structure yields a power conversion efficiency of 41.65% with open circuit voltage of 1.78V, short circuit current of 35.72mA/ cm2and fill factor of 90.16%. The performance of the GaAs/GaSb dual-junction solar cell was further improved by using sunlight concentration. A conversion power efficiency of 45.78% at 60sun light concentration was attained. It was found also that above this level of concentration ratio the detriment effect of shunt resistance dominates.

Cover Image

The cover image is based on the Research Article InGaP/GaAs dual-junction solar cells with AlInGaP passivation layer grown by hydride vapor phase epitaxy by Yasushi Shoji et al., https://doi.org/10.1002/pip.3454.

Counterbalancing light absorption and ionic transport losses in the electrolyte for integrated solar water splitting with III–V/Si dual-junctions

Recently, significant progress in the development of III–V/Si dual-junction solar cells has been achieved. This not only boosts the efficiency of Si-based photovoltaic solar cells but also offers the possibility of highly efficient green hydrogen production via solar water splitting. Using such dual-junction cells in a highly integrated photoelectrochemical approach and aiming for upscaled devices with solar-to-hydrogen (STH) efficiencies beyond 20%, however, the following frequently neglected contrary effects become relevant: (i) light absorption in the electrolyte layer in front of the top absorber and (ii) the impact of this layer on the Ohmic and transport losses. Here, we initially model the influence of the electrolyte layer thickness on the maximum achievable solar-to-hydrogen efficiency of a device with an Si bottom cell and show how the top absorber bandgap has to be adapted to minimize efficiency losses. Then, the contrary effects of increasing Ohmic and transport losses with the decreasing electrolyte layer thickness are evaluated. This allows us to estimate an optimum electrolyte layer thickness range that counterbalances the effects of parasitic absorption and Ohmic/transport losses. We show that fine-tuning of the top absorber bandgap and the water layer thickness can lead to an STH efficiency increase of up to 1% absolute. Our results allow us to propose important design rules for high-efficiency photoelectrochemical devices based on multi-junction photoabsorbers.