Multiple Quantum Well Solar Cells Research Articles

Optical design and bandgap engineering in ultrathin multiple quantum well solar cell featuring photonic nanocavity

AbstractUltrathin solar cells are efficient and captivating devices with unique technological and scientific features in terms of minimal material consumption, fast fabrication processes, and good compatibility with semi‐transparent applications. Such photovoltaic (PV) technologies can enable effective synergy between optical and electronic confinements with large tuning capabilities of all the optoelectronic characteristics. In this work, the implications of the optical design and the bandgap engineering in ultrathin hydrogenated amorphous Si/Ge multiple quantum well (MQW) solar cells featuring photonic nanocavity are analyzed based on experimental measurements and optoelectronic modelling. By changing the period thicknesses and the positions of QWs inside the deep‐subwavelength nanophotonic resonator, the spatial and spectral distributions of the optical field and the local absorption are strongly affected. This leads to a modulation of the absorption resonance condition, the absorption edge and the resulting photocurrent outputs. Because of quantum confinement effect, the change of MQW configurations with different individual QW periods while keeping similar total thickness of about 20 nm alters both the bandgap energy and the band offset at the QW/barrier heterojunctions. This in turn controls the photovoltage as well as the carrier collection efficiency in solar cells. The highest open circuit voltage and fill factor values are achieved by employing MQW device configuration with 2.5 nm‐thin QWs. A record efficiency above 5.5% is reached for such emerging ultrathin Si/Ge MQW solar cell technology using thinner QWs with sufficient number, because of the optimum trade‐off between all the optoelectronic characteristic outputs. The presented design rules for opaque ultrathin solar cells with quantum‐confined nanostructures integrated in a photonic nanocavity can be generalized for the engineering of relevant multifunctional semitransparent PV devices.

InGaP Solar Cell with InGaP Multiple Quantum Wells Grown under Optimized V/III Ratio

Indium gallium phosphide (InGaP) solar cells are widely used as top subcells in multi‐junction solar cells, however, there are large open‐circuit voltage (VOC) losses in InGaP solar cells. Improving the radiative efficiency by inserting an InGaP multiple quantum well (MQW) into the InGaP solar cell structure is a promising approach to enhancing the VOC of InGaP solar cells, but such InGaP MQW solar cells are not demonstrated. Moreover, the critical parameters, such as the V/III ratio for an InGaP MQW, are not investigated. This study investigates the optimal V/III ratio for enhancing the radiative efficiency of an InGaP MQW. Doublehetero structures are fabricated, comprising a 330 nm core layer with 55 periods of an InGaP MQW grown under varying V/III ratios. The InGaP MQW grown under V/III = 62 gives the highest photoluminescence intensity among all InGaP structures. An InGaP MQW solar cell grown at V/III = 62 exhibits a 2 mV VOC loss suppression compared with an InGaP bulk solar cell. Therefore, an InGaP MQW grown under proper growth conditions contributes to enhance the energy conversion efficiency of InGaP solar cells. This study provides relevant insights into InGaP MQW crystal growth and the performance improvement in InGaP solar cells.

Optically Induced Degradation Due to Thermally Activated Diffusion in GaN-Based InGaN/GaN MQW Solar Cells

We extensively investigate the degradation of gallium nitride (GaN)-based high periodicity indium GaN (InGaN)-GaN multiple quantum well (MQW) solar cells submitted to optical stress at high excitation intensity and high temperature. The original results reported in this article indicate the presence of a thermally activated diffusion of impurities from the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${p}$ </tex-math></inline-formula> -side of the devices toward the active region (AR), which favors the increase in the Shockley–Read–Hall (SRH) recombination within the MQWs. Appropriate fitting of the degradation kinetics according to Fick’s second law allowed the extrapolation of the diffusion coefficient of the defect involved in the degradation and of the related activation energy. The obtained values suggest that degradation originates from the diffusion of hydrogen. The proposed analytical methodology and the related results provide insight on MQW solar cells degradation and can be used to increase cell performance and reliability in novel applications and harsh environments.

Novel semi‐transparent solar cell based on ultrathin multiple Si/Ge quantum wells

AbstractUnlike conventional opaque solar cells, semi‐transparent solar cells enable simultaneous electricity generation and light transmission. Along with solar energy harvesting, the offered multiple functionalities of these technologies, such as aesthetic appearance, visual comfort and thermal management, open diverse integration opportunities into versatile technological applications. In this work, the first demonstration of a novel semi‐transparent solar cell based on ultrathin hydrogenated amorphous Si/Ge multiple quantum wells (MQW) is reported. Through optoelectronic modelling, the advantages of ultrathin MQW as photoactive material to overcome the intrinsic limitations of thin (20 nm) and ultrathin (2.5 nm) single quantum well (SQW) counterparts are explained. This allows extra degree of freedom for both optical design and bandgap engineering. Mainly, the multiplication of the QWs number in a periodic configuration, taking advantage of effective synergy between electronic and photonic confinements, leads to an improvement of photocurrent, while preserving high voltage and fill factor and ensuring significant transparency. The MQW new concept yields a boost in power conversion efficiency up to 3.4% and a considerable average visible transmission of about 33%. A light utilization efficiency above 1.1% is achieved, which can be considered as one of the highest among inorganic semi‐transparent solar cell technologies. The successful demonstration of ultrathin semi‐transparent Si/Ge MQW solar cells indicates the promising integration potential of this emerging photovoltaic technology for supplying systems in relevant applications such as in buildings, vehicles and greenhouses.

Role of p-GaN layer thickness in the degradation of InGaN-GaN MQW solar cells under 405 nm laser excitation

GaN-based solar cells with InGaN multiple quantum wells (MQWs) are promising devices for application in space environment, concentrator solar systems, wireless power transmission and multi-junction solar cells. It is therefore important to understand their degradation kinetics when submitted to high-temperature and high-intensity stress. We submitted three samples of GaN-InGaN MQW solar cells with p-AlGaN electron-blocking-layer with different thickness of the p-GaN layer to constant power stress at 310 W/cm2, 175 °C for several hundred hours. The main degradation modes are a reduction of open-circuit voltage, short-circuit current, external quantum efficiency, power conversion efficiency and electroluminescence. In particular, we observed that a thinner p-GaN layer results in a stronger degradation observed on the cell operating parameters. The analysis of the dark I-V characteristics showed an increase in low-forward bias current and the analysis of electroluminescence showed a decrease in the electroluminescene emitted by the (forward biased) cell, as a consequence of stress. This work highlights that the cause of degradation is possibly related to a diffusion mechanism, which results in an increase of defect density in the active region. The impurities involved in the diffusion processes possibly originate from the p-side of the devices, therefore a thicker p-GaN layer reduces the amount of defects reaching the active region.

Determination of Enriched Quantum Efficiency with InGaN/GaN Multiple Quantum Well Solar Cells

Background: Energy is a major concern in every aspect of our life. Solar energy is a renewable environmentally friendly source of energy. Therefore, solar cells are vastly studied with different technology and different material. Objective: The main objective here is to analyze InGaN material for solar cell applications with less complicated structures of MQW solar cells on revising solar cell with the recombination structure, I-V characteristics, and its efficiency. Methods: The device is simulated using SILVACO ATLAS, where the well and the barrier layers are inserted in the depletion region employing material combination of InGaN / GaN, which increases the solar cell performance parameter. This work focuses on the photogeneration rate, recombination in the active region as well as its current-voltage relation from the simulation. Results: With the increase in the number of QW periods in the active region of the device, the photovoltaic parameters especially conversion efficiency, increases significantly. Under space AM0 solar illumination, the cell efficiency increases up to 8.2 % for 20 MQWs with 20% Indium content for the InGaN/GaN structure. It enhances the External Quantum Efficiency (EQE) upto 36% at nearly 380nm wavelength range near the UV region. Conclusion: The modelled structure is efficiently simulated using TCAD SILVACO ATLAS, and the material Indium Gallium Nitride semiconductor shows an excellent solar cell performance with high solar radiation. It is also observed that with an increase in the number of well periods the solar cell performance increases, which demonstrates the feasibility of Indium Gallium Nitride solar cell with an additional MQW period as a power source.

Effect of Hydrostatic Pressure on Optical Absorption Coefficient of InGaN/GaN of Multiple Quantum Well Solar Cells

In this paper, a numerical model is used to analyze an optical absorption coefficient according to the electronic properties of InGaN/GaN multiple-quantum-well solar cells (MQWSC) under hydrostatic pressure. Finite difference techniques have been used to acquire energy eigenvalues and their corresponding eigenfunctions of InGaN/GaN MQWSC and the hole eigenstates are calculated via a 6*6 k.p method under the applied hydrostatic pressure. All symmetry-allowed transitions up to the fifth subband of the quantum wells (multi-subband model) and barrier optical absorption, as well as the linewidth due to the carrier-carrier and carrier-longitudinal optical (LO) phonon scattering, are considered here. A change in the pressure up to 10 GPa increases the intraband scattering time up to 38fs and 40fs for light and heavy holes, respectively, raises the height of the Lorentz function and reduces the excitonic binding energy. The multi-subband model has a positive effect on the optical absorption coefficient and increases it by %17, contrary to the pressure function.

Numerical modeling of electronic and electrical characteristics of InGaN/GaN multiple quantum well solar cells

Numerical model was developed to analyze photovoltaic parameters according to electronic properties of InGaN/GaN multiple quantum well solar cell (MQWSC) under hydrostatic pressure. Finite difference method was used to acquire energy eigenvalues and their corresponding eigenfunctions of InGaN/GaN MQWSC and hole eigenstates were calculated using a 6 × 6 k.p method under an applied hydrostatic pressure. Our results show that depth of quantum wells, bandgaps, band offset, electron, and hole density increase with the increase in the hydrostatic pressure. Also as pressure was increased, electron and hole wave functions had less overlap, amplitude of absorption coefficient was increased, and binding energy of excitons was decreased. A change in pressure of up to 10 GPa caused absorption coefficient’s peaks of light and heavy holes to shift to low wavelengths of up to 32 nm, along with decreased current density of short circuit, increased open circuit voltage, and enhanced efficiency of InGaN/GaN MQWSC.

Investigation of DIBS-Deposited CdZnO/ZnO-Based Multiple Quantum Well for Large-Area Photovoltaic Application

Multiple quantum wells (MQWs) of CdZnO/ZnO are realized, for the first time, by dual ion beam sputtering (DIBS) system at different deposition conditions in terms of ion beam power, substrate temperature, and time cessation between deposition of successive layers. The effects of DIBS deposition conditions are analyzed by secondary ion mass spectroscopy (SIMS) and high-resolution transmission electron microscopy (HRTEM) and discussed systematically. The SIMS analysis has been used for depth profiling of CdZnO/ZnO-based MQWs structure. The deposition of CdZnO/ZnO-based MQW structure performed at 100 °C with time cessation of 30 min between successive layer growth and ion beam power of 14 W has displayed the best results in terms of distinct well and barrier layers formation. This work also includes an analytical study of CdZnO/ZnO-based MQW solar cell (MQWSC), in which a study is performed for solar irradiance dependence of performance parameters to explore the potential use of CdZnO/ZnO-based MQWSC for concentrator solar cell (SC). The short-circuit current density increases from 0.12 to 57.98 mA/cm2, the open-circuit voltage rises from 2.60 to 2.77 V, and the photon conversion efficiency is from 2.85% to 3.04%, as solar irradiance increases from 0.1 to 50 suns. The results show that the performance of SCs can be improved by using concentrators and also explore the possibility of efficiently absorbing short-wavelength photons.

GaN-based high-periodicity multiple quantum well solar cells: Degradation under optical and electrical stress

We investigate the degradation of InGaN-GaN MQW solar cells under optical and electrical stress. We submitted the devices to high temperature, high optical power stress and we found that, under optical stress, the devices show a moderate decrease in open-circuit voltage, possibly due to creation of defect-related shunt paths. This degradation is partially recovered after room temperature storage. The stronger decrease of open-circuit voltage under electrical stress at high current suggests a role of carrier flow in the degradation.

InGaN/GaN multi‐quantum‐well solar cells under high solar concentration and elevated temperatures for hybrid solar thermal‐photovoltaic power plants

AbstractHybrid solar electricity generation combines the high efficiency of photovoltaics (PVs) with the dispatchability of solar thermal power plants. Recent thermodynamic analyses have shown that the most efficient strategy constitutes an integrated concentrating PV‐thermal absorber operating at high solar concentration and at the high temperatures suitable to efficient commercial steam turbines (~673–873 K). The recuperation of PV thermalization losses and the exploitation of sub‐bandgap photons can more than compensate for the inherent decrease of PV efficiency with temperature in properly tailored tandem solar cells for which promising candidates are III–N alloys. Recently, there have been considerable efforts to develop apposite InGaN solar cells by producing InGaN/GaN multiple quantum wells (MQWs) as the top cell in a tandem PV device that would absorb the short‐wavelength regime of the solar spectrum, while sub‐bandgap photons and PV thermalization are absorbed in the thermal receiver.We present measurements of current–voltage curves and external quantum efficiency spectra for InGaN/GaN MQW solar cells under high sunlight intensity, up to 1 W/mm2 (1000 suns) and elevated temperature, up to 723 K. We find that the short‐circuit current increases significantly with temperature, while the magnitude of the temperature coefficient of the open‐circuit voltage decreases with solar concentration according to basic photodiode theory. Conversion efficiency peaks at 623–723 K under ~300 suns, with no perceptible worsening in cell performance under extensive temperature and irradiance cycling—an encouraging finding in the quest for high‐temperature high‐irradiance cells.

Performance optimization of solar cells using non-polar, semi-polar and polar InGaN/GaN multiple quantum wells alongside AlGaN blocking layers

This paper reports opto-electronic properties and photo-voltaic performances of non-polar, semi-polar and polar solar cells employing InGaN/GaN multiple quantum wells (MQWs) with and without using AlGaN material as electron and hole blocking layers. In addition, the investigation is conducted for a number of QWs, e. g., 3, 5, 7, and 10. The performance of such devices is evaluated in terms of current density–voltage characteristics, power–voltage characteristics, fill factor, and power conversion efficiency. Our TCAD simulation results show that the InGaN/GaN solar cell featuring non-polar crystal structure, seven QWs alongside AlGaN blocking layers turns out to be the optimised device exhibiting open circuit voltage (Voc) of 1.08 V, short circuit current density (Jsc) of − 7.64 mA/cm2 and power conversion efficiency (η) of 5.36% among all other solar cells. The optimized device exhibits a considerably high value of η compared to earlier findings of nitride based solar cells. Hence our present design for InGaN/GaN MQW solar cells could provide an encouraging guideline for design and development of solar cells utilizing III–V nitride semiconductors in near future.

Analytical Performance Analysis of CdZnO/ZnO-Based Multiple Quantum Well Solar Cell

This article presents analytical and simulation evaluation of multiple quantum well solar cells (MQWSC) with CdZnO/ZnO as the intrinsic layer, Sb-doped ZnO (SZO) as a p-type layer, and Ga-doped ZnO (GZO) as an n-type layer of the p-i-n solar cell (SC). The material parameters used in this article are obtained from the experimental reports on the properties of ZnO and CdZnO thin films grown by dual-ion-beam sputtering (DIBS). The American Society for Testing and Materials (ASTM) standards data sheets have been utilized for attaining photon flux density instead of the blackbody radiation formula. The analytically obtained results show good agreement with the simulated results obtained by the ATLAS simulation tool. The variation of device performance parameters is examined for thermal stability. The results show that, for the proposed ZnO-based MQWSC, the open-circuit voltage ( ${V}_{{\text {oc}}}$ ) has a negative temperature coefficient (−2.63 mV/°C), and short-circuit current density ( ${J}_{{\text {sc}}}$ ) and conversion efficiency ( ${\eta }$ ) have positive temperature coefficients of $2.43\times 10^{{-{3}}} \,\,{\text {mA}/\text {cm}^{{{2}}}\cdot ^{\circ }}\text{C}$ and $2.91\times 10^{{-{3}}}$ %/°C, respectively. Further, the device performance has been explored for variation in the number of quantum wells. The results present that an increase in the number of quantum wells has a negative impact on the performance parameters of ZnO-based MQWSC.

Study of hole-blocking and electron-blocking layers in a InaS/GaAs multiple quantum-well solar cell

In this work, a GaAs-based quantum well solar cell with a 25-layer InAs/GaAs intermediate layer is simulated in Silvaco Atlas TCAD software. In order to reduce the recombination caused by the presence of the quantum layers and increase the absorption of photons, electron blocking layers (EBLs) and hole blocking layers (HBLs) have been added to the solar cell in an In0.5(Al0.7Ga0.3)0.5P semiconductor. The results show that the efficiency of the proposed solar cell increases 17.38% by obtaining impurity the thickness and doping of the EBL and HBL layers. It can be concluded that the use of the In0.5(Al0.7Ga 0.3)0.5P semiconductor with EBL and HBL layers decreases the open circuit voltage (Voc) caused in the quantum wells. The efficiency of the proposed solar cell with EBL and HBL layers was found to be 44.65%.

Analytical Study of Performance Parameters of InGaN/GaN Multiple Quantum Well Solar Cell

An analytical study has been carried out to obtain the device performance parameters of InGaN/GaN-based multiple quantum well solar cell (MQWSC). Significant improvements are made upon the preexisting models reported in the literature for predicting device performance matrix for MQWSC. The American Society for Testing and Materials (ASTM) standards data sheets are utilized for attaining photon flux density instead of blackbody radiation formula. Furthermore, the photon flux density is utilized to evaluate the performance parameters of MQWSC and bulk p-i-n solar cell. Results suggest that by incorporating QWs in the intrinsic region ( ${x} = {0.1}$ in $\text{In}_{x}\text{Ga}_{{1}-{x}}\text{N}$ ), ∼27% increment in the conversion efficiency can be achieved as compared to that from the bulk solar cell. Moreover, the impact of operating temperature in the solar cell performance is also studied. The rise in temperature leads to an increase in short-circuit current density; however, open-circuit voltage and conversion efficiency decrease. A decrement of ∼9.7% in the conversion efficiency of MQWSC is observed with the rise in temperature from 200 to 400 K as compared to ∼11.6% decline in p-i-n solar cell.

Numerical Modeling of the Electronic and Electrical Characteristics of InGaN/GaN-MQW Solar Cells

In this paper, a numerical model allows to analyze the photovoltaic parameters according to the electronic properties of InxGa1−xN/GaN MQW solar cells under the effect of temperature, the number of quantum wells and indium composition. The numerical investigation starts from the evaluation through the finite difference (FDM) simulation of the self-consistent method coupled with the photovoltaic parameters taking into account the effects of the spontaneous and piezoelectric polarization. The results found were consistent with the literature. As expected, the temperature had a negative impact on the performance of InGaN/GaN MQW solar cells. However, increasing the number of quantum wells improves cell performance. This positive impact further improves with the increase in the indium rate. The obtained results were 28 mA/cm2 for the short-circuit current density, 1.43 V for the open-circuit voltage, and the obtained conversion efficiency was 31% for a model structure based on 50-period InGaN/GaN-MQW-SC under 1-sun AM1.5G.

Effect of Indium Composition on the Microstructural Properties and Performance of InGaN/GaN MQWs Solar Cells

In the present work, InGaN/GaN multiple quantum wells (MQWs) solar cells with different concentrations of indium have been investigated in-depth. It was demonstrated that applying a medium-high indium content (about 28%) does not facilitate solar cell photoelectric conversion efficiency due to the increase of edge dislocations. Moreover, the effects of different indium contents on InGaN/GaN MQWs solar cells were investigated and was revealed, that the short-circuit current density and photoelectric conversion efficiency are improved with the increase of indium contents. However, they show a noticeable reduction in the indium content of 28%. Furthermore, the optical properties and the behaviour of the microstructure defects were analysed. It was also demonstrated that the number of edge dislocations acted as non-radiation recombination centers increasing rapidly when the indium content reaches 28%, playing a key role in decreasing the active number of photon-generated carriers. As a result, the short-circuit current density and photoelectric conversion efficiency decrease obviously for an indium content of 28%. This work can provide insight into the origin of the degradation of these structures and the improvement of device design with medium-high indium contents.

Temperature Dependence of InGaN / GaN Multiple Quantum Well Solar Cells

Elements based on nitride family and more specifically, those of the GaN/InGaN family, present a great interest for renewable energy conversion systems as they offer huge potentialities in photovoltaic applications, as example for the realization of concentration solar cells. This interest is linked to the possibility to enlarge the part of the solar energetic spectrum that a solar cell is able to capture thanks to the possibilities of growing multilayers cells with various band-gap and thus, with various absorption bands. In this paper, the performance of InGaN/GaN multiple quantum well MQW solar cells with respect to the N-polar orientation. is investigated. In order to obtain the exact conversion efficiency, the temperature effect as well as the spontaneous and piezoelectric polarization effect are taking into consideration in model. The results reveal that the increase of temperature decreases significantly the MQW solar cell efficiency.Our results and discussion would be helpful in designing and fabricating high efficiency InGaN/GaN solar cell in experiment.

Abnormal staircase-like I-V curve in InGaN quantum well solar cells

InGaN/GaN multiple quantum well-solar cells with different barrier thicknesses have been comparatively studied, and it is demonstrated that a thinner barrier facilitates the transport of photogenerated carriers. Meanwhile, an abnormal but regular staircase-like I-V curve is observed. The induction factors and microscopic physical process relevant to this abnormal feature are analyzed in detail, which is found closely related to the inadequate internal field and special epitaxial structure. Furthermore, the formation conditions of I-V curves with various types of inflections are also proposed. This work provides insight into the origin of device problems, which can be applicable to other types of solar cells.

Proton Radiation Effect on InGaN/GaN Multiple Quantum Wells Solar Cell

An enhanced InGaN/GaN multiple-quantum-wells (MQWs) solar cell was exposed to 3 MeV protons. The performance of the solar cell, including the current-voltage characteristics and external quantum efficiency (EQE), degraded after irradiation with 3 MeV protons. The ideality factor became higher with increased proton fluence, which indicates defects were introduced into the device. The decreased peak intensity and increased full width at half maximum (FWHM) in photoluminescence (PL) spectra from InGaN, and the increased FWHM values of the InGaN satellite peaks from (002) ω–2θ diffraction curves all indicate the active region degraded. Moreover, according to the correlation between the ideality factor, the negative of one-thousandth of InGaN peak intensity, and FWHM of the PL spectra in the active region, we deduced that defects were introduced in the active region. Furthermore, we deduced the defects are Ga vacancies using SRIM software simulation. The enhanced yellow band may be affected by Ga vacancies since the other influencing factors in our experiment could be excluded. Based on the above analysis, we infer that Ga vacancies may be introduced in the active region after irradiation with 3 MeV proton, which may lead to degraded electrical parameters in InGaN/GaN MQWs solar cells.