Dual Junction Research Articles

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.

Mechanically Stacked Solar Cells for Concentrator Photovoltaics

The power output of dual-junction mechanically stacked solar cells comprising different sub-cell materials in a terrestrial concentrating photovoltaic module has been evaluated. The ideal bandgap combination of both cells in a stack was found using EtaOpt. A combination of 1.4 eV and 0.7 eV has been found to produce the highest photovoltaic conversion efficiency under the AM1.5 Direct Solar Spectrum with x500 concentration. As EtaOpt does not consider the absorption profile of solar cell materials; the practical power output per unit area of a dual junction mechanically stacked solar cell has been modelled considering the optical absorption co-efficients and thicknesses of the individual solar cells. The model considered a GaAs top cell and a Ge, GaSb, Ga0.47In0.53As or Si bottom cell. It was found that GaSb gives the highest power contribution as a bottom cell in a dual junction configuration followed by Ge and GaInAs. While the additional power provided by a Si bottom cell is less than these it remains a suitable candidate for a bottom cell owing to its lower cost.

Design of interfacial dual Schottky junctions to modulate charge transfer for enhanced piezo-assisted photocatalytic degradation RhB performances

Construction of piezo-assisted interfacial dual Schottky junction to regulate charge transfer and surface reaction rate for the photocatalytic degradation of RhB.

Electron-distribution control via Pt/NC and MoC/NC dual junction: Boosted hydrogen electro-oxidation and theoretical study

The scarcity, high cost and susceptibility to CO of Platinum severely restrict its application in alkaline hydrogen oxidation reaction (HOR). Hybridizing Pt with other transition metals provides an effective strategy to modulate its catalytic HOR performance, but at the cost of mass activity due to the coverage of modifiers on Pt surface. Herein, we constructed dual junctions’ Pt/nitrogen-doped carbon (Pt/NC) and δ-MoC/NC to modify electronic structure of Pt via interfacial electron transfer to acquire Pt-MoC@NC catalyst with electron-deficient Pt nanoparticles, simultaneously endowing it with high mass activity and durability of alkaline HOR. Moreover, the unique structure of Pt-MoC@NC endows Pt with a high CO-tolerance at 1,000 ppm CO/H2, a quality that commercial Pt-C catalyst lacks. The theoretical calculations not only confirm the diffusion of electrons from Pt/NC to MoC/NC could occur, but also demonstrate the negative shift of Pt d-band center for the optimized binding energies of *H, *OH and CO.

Synchronous regulation of Schottky/p-n dual junction in Prussian blue-derived Janus heterostructures: A path to ultrafast long life potassium ion batteries

Synchronous regulation of Schottky/p-n dual junction in Prussian blue-derived Janus heterostructures: A path to ultrafast long life potassium ion batteries

Deep Electronic State Regulation through Unidirectional Cascade Electron Transfer Induced by Dual Junction Boosting Electrocatalysis Performance.

Unidirectional cascade electron transfer induced by multi-junctions is essential for deep electronic state regulation of the catalytic active sites, while this advanced concept has rarely been investigated in the field of electrocatalysis. In the present work, a dual junction heterostructure (FePc/L-R/CN) is designed by anchoring iron phthalocyanine (FePc)/MXene (L-Ti3 C2 -R, R═OH or F) heterojunction on g-C3 N4 nanosheet substrates for electrocatalysis. The unidirectional cascade electron transfer (g-C3 N4 → L-Ti3 C2 -R → FePc) induced by the dual junction of FePc/L-Ti3 C2 -R and L-Ti3 C2 -R/g-C3 N4 makes the Fe center electron-rich and therefore facilitates the adsorption of O2 in the oxygen reduction reaction (ORR). Moreover, the electron transfer between FePc and MXene is facilitated by the axial Fe─O coordination interaction of Fe with the OH in alkalized MXene nanosheets (L-Ti3 C2 -OH). As a result, FePc/L-OH/CN exhibits an impressive ORR activity with a half-wave potential (E1/2 ) of 0.92V, which is superior over the catalysts with a single junction and the state-of-the-art Pt/C (E1/2 = 0.85V). This work provides a broad idea for deep regulation of electronic state by the unidirectional cascade multi-step charge transfer and can be extended to other proton-coupled electron transfer processes.

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.

(Invited) Emergent Absorbers, Interfaces, and Integration Methods for Chalcopyrite-Based Photoelectrochemical Water Splitting Devices

Photoelectrochemical (PEC) water splitting has the potential to become an efficient method for renewable hydrogen production. However, the efficiency, projected cost, and durability of lab-scale systems are not yet at the level required to make this technology economically feasible. Amongst all materials studied to date, the chalcopyrite class is arguably one of the most promising classes for PEC water splitting, as it has already demonstrated low-cost and high photoconversion capabilities as a photovoltaic material. In the context of PEC, our group demonstrated that co-evaporated 1.65 eV bandgap (EG) CuGaSe2 is capable of evolving hydrogen with Faradaic efficiency greater than 85% and generate photocurrent densities over 15 mA.cm-2, as measured in a 3-electrode configuration in 0.5M H2SO4 under simulated AM1.5G illumination. Unfortunately, CuGaSe2’s narrow EG limits its integration as top absorber into a dual junction stacked PEC device (also known as hybrid photoelectrode, HPE). In the present communication, we report on our latest efforts to synthesize wide-EG (1.8-2.0 eV) chalcopyrites, compatible with the HPE integration scheme, and capable of generating saturated photocurrent densities greater than 10 mA/cm2. We present specifically results on EG tunable Cu(In,Ga)(S,Se)2, Cu(In,Ga)S2, CuGa(S,Se)2 and CuGa3Se5. We also discuss some of the strategies developed to improve their surface energetics for the hydrogen evolution reaction, including the use of bandgap tunable MgZnO n-type buffer layers. Finally, we introduce the concept of semi-monolithic tandems, a new integration scheme where wide- and narrow-bandgap chalcopyrites are first integrated on separate substrates and then exfoliated, and finally bonded to create fully functional tandem device.

Impact of trap-related non-idealities on the performance of a novel TFET-based biosensor with dual doping-less tunneling junction

This article presents a novel dielectric-modulated biosensor based on a tunneling field-effect transistor. It comprises a dual doping-less tunneling junction that lies above an n+ drain region. By employing the wet-etching technique, two cavities are carved in the gate dielectric, and with the entry of various biomolecules into the cavities, the electrostatic integrity of the gate changes, accordingly. Numerical simulations, carried out by the Silvaco ATLAS device simulator, show that including trap-assisted tunneling significantly modulate the biosensor's main parameters, such as on-state current, subthreshold swing, and transconductance and their corresponding sensitivities. We also evaluate the effect of semi-filled cavities on our proposed biosensor’s performance with various configurations. The FOMs like Ion/Ioff = 2.04 × 106, {S}_{{I}_{ds}}=1.48 × 105, and {S}_{SS}=0.61 in the presence of TAT show that our proposed biosensor has a promising performance.

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.

Photovoltaics literature survey (no. 182)

Photovoltaics literature survey (no. 182)

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.

A Novel Vertical Si TFET With Dual Doping-Less Tunneling Junction: A Simulation Study Including Trap-Related Non-Idealities

A Novel Vertical Si TFET With Dual Doping-Less Tunneling Junction: A Simulation Study Including Trap-Related Non-Idealities

Integration of photovoltaic and photogating effects in a WSe2/WS2/p-Si dual junction photodetector featuring high-sensitivity and fast-response.

Two-dimensional (2D) material-based van der Waals (vdW) heterostructures with exotic semiconducting properties have shown tremendous potential in next-generation photovoltaic photodetectors. Nevertheless, these vdW heterostructure devices inevitably suffer from a compromise between high sensitivity and fast response. Herein, an ingenious photovoltaic photodetector based on a WSe2/WS2/p-Si dual-vdW heterojunction is demonstrated. First-principles calculations and energy band profiles consolidate that the photogating effect originating from the bottom vdW heterojunction not only strengthens the photovoltaic effect of the top vdW heterojunction, but also suppresses the recombination of photogenerated carriers. As a consequence, the separation of photogenerated carriers is facilitated and their lifetimes are extended, resulting in higher photoconductive gain. Coupled with these synergistic effects, this WSe2/WS2/p-Si device exhibits both high sensitivity (responsivity of 340 mA W-1, a light on/off ratio greater than 2500, and a detectivity of 3.34 × 1011 Jones) and fast response time (rise/decay time of 657/671 μs) under 405 nm light illumination in self-powered mode. Finally, high-resolution visible-light and near-infrared imaging capabilities are demonstrated by adopting this dual-heterojunction device as a single pixel, indicating its great application prospects in future optoelectronic systems.

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.

A High Performance MRAM Cell Through Single Free-Layer Dual Fixed-Layer Magnetic Tunnel Junction

As technology size scales down, magnetic tunnel junctions (MTJs) as a promising technology are becoming more and more sensitive to process variation, especially in oxide barrier thickness. Process variation particularly affects the cell resistance and the critical switching current for the smaller dimensions. This article proposes an MTJ cell with one free and two pinned layers, which highly improves the process variation robustness. By employing the spin transfer torque (STT)-spin-Hall effect (SHE) switching method, our proposed MTJ cell improves the switching speed and lowers the switching power consumption. Per simulations, an MRAM cell built with the proposed MTJ cell offers up to 36% lower total power consumption, up to 32% higher write performance, and 35% higher read performance over the previous state-of-the-art MRAMs. Also, the error rate resulting from process variation is 1.4%, which is about one-tenth of the best examples reported in the literature.

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.