Quantum Dot Intermediate Band Research Articles

Theoretical Investigation and Improvement of Characteristics of InAs/GaAs Quantum Dot Intermediate Band Solar Cells by Optimizing Quantum Dot Dimensions

Quantum dot (QD)-based solar cells have been the focus of extensive research. One of the critical challenges in this field is optimizing the size and placement of QDs within the cells to enhance light absorption and overall efficiency. This paper theoretically investigates InAs/GaAs QD intermediate band solar cells (QD-IBSC) employing cylindrical QDs. The goal is to explore factors affecting light absorption and efficiency in QD-IBSC, such as the positioning of QDs, their dimensions, and the spacing (pitch) between the centers of adjacent dots. Achieving optimal values to enhance cell efficiency involves modifying and optimizing these QD parameters. This study involves an analysis of more than 500 frequency points to optimize parameters and evaluate efficiency under three distinct conditions: output power optimization, short-circuit current optimization, and generation rate optimization. The results indicate that optimizing the short-circuit current leads to the highest efficiency compared to the other conditions. Under optimized conditions, the efficiency and current density increase to 34.3% and 38.42 mA/cm2, respectively, representing a remarkable improvement of 15% and 22% compared to the reference cell.

Structural optimization and engineering of InxGa1−xN quantum dot intermediate band solar cells with intrinsic GaN interlayers

We proposed an optical structure to enhance photoelectric efficiency by optimizing 1 nm i-GaN layers to compensate for lattice mismatch from the In0.5Ga0.5N/GaN layer and absorb excess strain, boosting efficiency.

High-efficiency InAs/GaAs quantum dot intermediate band solar cell achieved through current constraint engineering

In this work, a novel device concept for improving the efficiency and field operation of conventional InAs/GaAs quantum dot (QD) based intermediate band solar cell (IBSC) with the feature of current constraint (CC-QD-IBSC) was proposed and evaluated from both theoretical simulations and experimental demonstrations. The advantages of the proposed device concept including increasing efficiency, obtaining higher suitability for operation under concentrated photovoltaic (CPV) condition and more robust efficiency stability against intermediate band fluctuation were rigorously identified using the detailed balance theorem by comparing with conventional InAs/GaAs QD-IBSC. Furthermore, a hybrid molecular beam epitaxy (MBE) and metal organic chemical vapor deposition (MOCVD) shuttle growth of the proposed CC-QD-IBSC were adopted in this work for better preserving QD induced intermediate band feature and overcoming practical growth difficulties. By introducing a InGaP top cell for constraining the current of InAs/GaAs QD-IBSC, the short circuit current density of CC-QD-IBSC decreased to 13.0mA/cm2 under 1 sun illumination, a near 50 % reduction compared to the conventional InAs/GaAs QD-IBSC. On the contrary, by well adjusting the regrowth interface between MBE and MOCVD, we managed to reach the highest conversion efficiency of 22.8 % measured at an UL certified laboratory under light concentration ratio of 93 suns for the proposed CC-QD-IBSC with well-functioning QD and IB feature. It is our belief that our results pave the road for developing techniques geared towards higher efficiency and more practical field applications.

Enhancing intermediate band solar cell performances through quantum engineering of dot states by droplet epitaxy

AbstractWe report the effect of the quantum dot aspect ratio on the sub‐gap absorption properties of GaAs/AlGaAs quantum dot intermediate band solar cells. We have grown AlGaAs solar cells containing GaAs quantum dots made by droplet epitaxy. This technique allows the realization of strain‐free nanostructures with lattice matched materials, enabling the possibility to tune the size, shape, and aspect ratio to engineer the optical and electrical properties of devices. Intermediate band solar cells have been grown with different dot aspect ratio, thus tuning the energy levels of the intermediate band. Here, we show how it is possible to tune the sub‐gap absorption spectrum and the extraction of charge carriers from the intermediate band states by simply changing the aspect ratio of the dots. The tradeoff between thermal and optical extraction is in fact fundamental for the correct functioning of the intermediate band solar cells. The combination of the two effects makes the photonic extraction mechanism from the quantum dots increasingly dominant at room temperature, allowing for a reduction of the open circuit voltage of only 14 mV, compared to the reference cell.

Enhanced current generation in quantum-dot intermediate band solar cells through optimizing the position of quantum dot layers

We present a numerical study using a self-consistent drift-diffusion approach to characterize the effect of light trapping on the quantum efficiency (QE) of a thin-film quantum dot intermediate band solar cell (QD-IBSC). In the concept of the IBSCs, the photons with energies lower than the bandgap of the host material can be absorbed in QDs due to the presence of the IB, leading to high photocurrent and conversion efficiency. However, in general, the quality of the QD structure is degraded due to the accumulated strain when the number of QD layers stacked vertically is increased, which is required to increase light absorption. In the present work, we adopted a Fabry-Pérot (FP) resonance structure to achieve high absorption with fewer QD layers. We demonstrate numerically, in a InAs/GaAs-based QDSC structure, that an increase in the QE by 8 times at maximum is achievable by tuning the position of the QD layers inserted.

Numerical Investigation into Photovoltaic Performance of Organolead Trihalide Perovskite Quantum Dot Intermediate Band Solar Cell

In this work, an intermediate band solar cell (IBSC) model consisting of MAPbI3 quantum dots (QD) and MAPbCl3 barrier material is explored analytically with MATLAB. Titanium di-oxide (TiO2) is used as transport layer for electron and Spiro-OMeTAD (2,2',7,7'-tet-rakis (N,N'-di-p-methoxyphenylamine)–9,9' spirobifluorene) is used as transport layer for hole. Fluorine-doped tin oxide (FTO) and Silver (Ag) is used as top and bottom contact. The impact of QD size and dot spacing on the key parameters of MAPbI3 QD-IBSC is illustrated throughout this paper. In order to identify the number of IB in a single regime, Schrödinger equation is solved as a function of host energy gap using Kronig–Penney model. The detailed balance limit assumptions with unity fill factor are applied to extract highest efficiency from the system. For any case, face centered cubic (FCC) crystal structure is assumed. The (100) crystal orientation is considered as charge carriers from n–region to p–region transport in this orientation. Major performance indicators of the device such as photocurrent intensity Jsc, open circuit voltage Voc and power conversion efficiency η have been delineated. Highest efficiency of 63% is attained for dot size of 4 nm and dot spacing of 1.5 nm.

Enhanced Current Generation in Quantum-Dot Intermediate Band Solar Cells Through Optimizing the Position of Quantum Dot Layers

Enhanced Current Generation in Quantum-Dot Intermediate Band Solar Cells Through Optimizing the Position of Quantum Dot Layers

The Role of Defects on the Performance of Quantum Dot Intermediate Band Solar Cells

Electrically active defects present in three InAs/GaAs quantum dots (QDs) intermediate band solar cells grown by metalorganic vapor phase epitaxy have been investigated. The devices’ structures are almost identical, differing only in the growth temperature and thickness of the GaAs layers that cover each InAs QD layer. These differences induce significant changes in the solar energy conversion efficiency of the photovoltaic cells, as previously reported. In this work, a systematic investigation was carried out using deep level transient spectroscopy (DLTS) and Laplace DLTS measurements on control samples and solar cell devices, which have clearly shown that electrically active traps play an important role in the device figures of merit, such as open circuit voltage, short circuit current, and shunt resistance. In particular, it was found that the well-known EL2 defect negatively affects both the open circuit voltage and shunt resistance, more in structures containing QDs, as a consequence of the temperature cycle required to deposit them. Other unidentified defects, that are absent in samples in which the QDs were annealed at 700 °C, contribute to a reduction of the short circuit current, as they increase the Shockley-Read-Hall recombination. Photoluminescence results further support the DLTS-based assignments.

Optimized Operation of Quantum-Dot Intermediate-Band Solar Cells Deduced from Electronic Transport Modeling

So far physics of quantum electronic transport has not tackled the problems raised by quantum dot intermediate-band solar cells. Our study shows that this physics imposes design rules for the inter-subband transition. We developed an analytical model that correctly treats, from a quantum point-of-view, the trade-off between the absorption, the recombination and the electronic transport occurring in this transition. Our results clearly indicate that it is essential to control the transit rate between the excited state of the quantum dot and the embedding semiconductor. For that, we propose to assume the dot in a tunnel-shell whose main characteristics can be obtained by a simple analytical formula. Moreover, we show that in a realistic case, the energy transition only needs to be larger than 0.28 eV to obtain a quasi Fermi-level splitting. This quite small value designates the quantum dot solar cell as a serious candidate to be an efficient intermediate-band solar cell. This work gives a framework to design efficient inter-subband transitions and then opens new opportunities for quantum dot intermediate-band solar cells.

Internal polarization electric field effects on the efficiency of InN/In[formula omitted]N multiple quantum dot solar cells

In this work, we investigate the influence of the internal electric field induced by the polarization inside the active region of the p-i-n photodiode on the characteristics of InN/InxGa1-xN quantum dots intermediate band solar cell. Considering the conduction and valence band offsets, the electron and hole energy levels have been determined by solving analytically the corresponding Schrödinger equations. The hole level, usually neglected in similar studies, is taken into account to determine all the intermediate transitions. All parameters of multiple quantum dot solar cells such as open-circuit voltage, short-circuit current density and photovoltaic conversion efficiency are determined as functions of the indium content, the internal electric field, inter-dot distances and dot sizes. Our calculations show that determining the photovoltaic conversion efficiency (η) without taking into account the internal electric field leads to an overestimation of η.

Projected Performance of InGaAs/GaAs Quantum Dot Solar Cells: Effects of Cap and Passivation Layers

In this work, the effects of Al x Ga1– x As cap and passivation (such as SiO2, Si3N4, and HfO2) layers on the performance of InGaAs/GaAs-based quantum dot intermediate band solar cells (QDIBSCs) have been studied. The low surface recombination rate of ~103 per cm3s is achieved by optimizing the composition, $x =0.40$ , and thickness (200 nm) of the Al x Ga1– x As cap layer. The optical reflectance is also evaluated for devices with different passivation. The solar cell with Si3N4 shows the lowest reflectance of 10.53%. The photogeneration rate has been enhanced at the quantum dot region because of the improvement of the photocurrent provides by both cap and passivation layers. There is also an increment found in the average external quantum efficiency of 39.56% as compared to that of the bared conventional QDIBSC. As a result, the solar cell, with both Al0.40Ga0.60As cap and Si3N4 passivation layers, shows the conversion efficiency of 27.8%, which is higher than that of 21.6% for conventional In0.53Ga0.47AS/GaAs-based QDIBSC. These results indicate that GaAs-based QDIBSCs with both Al0.40Ga0.60As cap and Si3N4 passivation layers are promising for next-generation photovoltaic applications.

Physical insights into the effects of quantum dots size and temperature on efficiency of InAs/GaAs quantum dots intermediate band solar cell

The main problem of the photovoltaic conversion device is that low energy photons cannot excite charge carrier to the conduction band, so that the concept of the quantum dot solar cell is proposed in the intrinsic region of the p−i−n structure. In this work, numerical simulation has been proposed using the Matlab software. We simulate and measure the effects of quantum dots size and temperature on efficiency of GaAs p−i−n structure solar cells incorporating quantum dots (QDs) InAs under illumination. The results show that the efficiency of p−i−n solar cell depend strongly on size of QDs and temperature.

Quantum engineering of intrinsic losses in the diluted nitride InAsN quantum dot intermediate band solar cell

Intrinsic losses, including below-band gap, thermalization, mismatch angle, Carnot, and emission, are investigated in a structure of quantum dot intermediate band solar cells (QD-IBSCs). Owing to the excellent irradiance resistance of III-nitride material and reduction of Auger recombination processes, diluted nitride of InAsN is considered as quantum dot (QD) material. Then, AlPSb is considered as the barrier material according to the principles of intermediate band operation and the band structures of InAsN and AlPSb in which phosphorous molar fraction is optimized by the minimizing of total intrinsic losses. The engineering of QD size and period offers a way to engineer the confined energy levels within the QDs and ultimately the intrinsic losses. This was carried out with the help of a finite element model in the context of a three-dimensional Schrodinger equation created by means of MATLAB software and tight binding method, resulting in the minimum intrinsic loss of 55.18% for the InAs0.995N0.005 / AlP0.7 Sb0.3 QD-IBSC at 1-sun concentration.

Impact of heavy hole levels on the photovoltaic conversion efficiency of In Ga1−N/InN quantum dot intermediate band solar cells

Abstract We report a theoretical investigation of the photovoltaic conversion efficiency of solar cells based on the introduction of I n x G a 1 − x N / I n N quantum dot supracrystals arrayed in the i-region of a p − i − n photodiode. The position and width of intermediate bands induced by the discrete quantized energy levels of electrons and holes originating from QDs are determined by using the Kronig-Penney model. Thus, interband and intersubband transitions are determined for different dot sizes and inter-dot distances. Taking into account the hole level and its impact on the band offset usually neglected in the same studies, all characteristic parameters of the cell such as open circuit voltage, short circuit current density and photoelectric conversion efficiency are determined as a function of the I n -concentration, mean size and inter-dot spacing of QDs. The results show that the performances of this new generation of solar cell increase considerably and can be adjusted by controlling the size, inter-dot spacing and I n -concentration.

Control of simultaneous effects of the temperature, indium composition and the impact ionization process on the performance of the InN/InxGa1-xN quantum dot solar cells

The impact ionization in semiconductor materials is a process that produces multiple charge carrier pairs from a single excitation. This mechanism constitutes a possible road to increase the efficiency of the p-n and p-i-n solar cells junctions. Our study considers the structure of InN/InGaN quantum dot solar cell in the calculation. In this work, we study the effect of indium concentration and temperature on the coefficient θ of the material type parameter of the impact ionization process for a p(InGaN)-n(InGaN) and p(InGaN)-i(QDs-InN)-n(InGaN) solar cell. Next, we investigate the effect of perturbation such as temperature and indium composition on conventional solar cell’s (p(InGaN)-n(InGaN)) and solar cells of the third generation with quantum dot intermediate band IBSC (p(InGaN-i(QD-InN)-n(InGaN)) by analyzing their behaviour in terms of efficiency of energy conversion at the presence of the impact ionization process. Our numerical results show that the efficiency is strongly influenced by all of these parameters. It is also demonstrated that θ decreased with the increase of indium concentration and temperature which contributes to an overall improvement of the conversion efficiency.

Theoretical study of the effects of n-type doping in InAs/GaAs quantum dot layer on current–voltage characteristics of intermediate band solar cells

We theoretically investigated the current–voltage characteristics of InAs/GaAs quantum dot intermediate band solar cells (QD IBSCs) with different n-type doping concentrations in the QD layer. When the optical absorption coefficients are low, the QD layer negatively affects conversion efficiency because it acts as a recombination center. As the n-type doping concentration increases, the negative effect of the QD layer is gradually suppressed. When the optical absorption coefficients are high, the QD layer can induce additional energy conversion. As the n-type doping concentration increases, the positive effect of the QD layer is also gradually suppressed. The electron occupation factor in the intermediate band varies not only with the doping concentration but also with the output voltage, and in our simulation model n-type doping cannot improve the efficiency of the QD IBSCs.

Performance analysis of high efficiency InxGa1−xN/GaN intermediate band quantum dot solar cells

Abstract In this subsistent fifth generation era, InxGa1−xN/GaN based materials have played an imperious role and become promising contestant in the modernistic fabrication technology because of some of their noteworthy attributes. On our way of illustrating the performance, the structure of InxGa1−xN/GaN quantum dot (QD) intermediate band solar cell (IBSC) is investigated by solving the Schrodinger equation in light of the Kronig-Penney model. In comparison with p-n homojunction and heterojunction solar cells, InxGa1−xN/GaN IBQD solar cell manifests larger power conversion efficiency (PCE). PCE strongly depends on position and width of the intermediate bands (IB). Position of IBs can be controlled by tuning the size of QDs and the Indium content of InxGa1−xN whereas, width of IB can be controlled by tuning the interdot distance. PCE can also be controlled by tuning the position of fermi energy bands as well as changing the doping concentration. In this work, maximum conversion efficiency is found approximately 63.2% for a certain QD size, interdot distance, Indium content and doping concentration.

Type-II GaSb/GaAs quantum-dot intermediate band with extended optical absorption range for efficient solar cells

GaSb/GaAs type-II quantum-dot solar cells (QD SCs) have attracted attention as highly efficient intermediate band SCs due to their infrared absorption. Type-II QDs exhibited a staggered confinement potential, where only holes are strongly confined within the dots. Long wavelength light absorption of the QDSCs is enhanced through the improved carriers number in the IB. The absorption of dots depends on their shape, material quality, and composition. Therefore, the optical properties of the GaSbGaAs QDs before and after thermal treatment are studied. Our intraband studies have shown an extended absorption into the long wavelength region $$1.77 \, \upmu \text {m}$$. The annealed QDs have shown significantly more infrared response of $$7.2 \, \upmu \text {m}$$ compared to as-grown sample. The photon absorption and hole extraction depend strongly on the thermal annealing process. In this context, emission of holes from localized states in GaSb QDs has been studied using conductance–voltage (G–V ) characteristics.

Photovoltaic conversion efficiency of InN/InxGa1-xN quantum dot intermediate band solar cells

The behavior of InN/InxGa1-xN spherical quantum dots solar cell is investigated, considering the internal electric field induced by the polarization of the junction. In order to determine the position of the intermediate band (IB), we present an efficient numerical technique based on difference finite method to solve the 3D time-independent Schrödinger's equation in spherical coordinates. The resultant n×n Hamiltonian matrix when considering n discrete points in spatial direction is diagonalized in order to calculate energy levels. Thus, the interband and intersubband transitions are determined, taking into consideration the effect of the internal electric field, size dots, interdot distances, and indium content on the energy levels, optical transition, photo-generated current density, open-circuit voltage and power conversion efficiency of the QD-IBSCs.

Projected Performance of an InxGa1-xAs Quantum Dot Intermediate Band Solar Cell

Quantum Dot Intermediate Band Solar Cell (QDIBSC) is one of the emerging technologies in the solar photovoltaic arena, which has immense potential to be demonstrated as a high efficiency device. For a QDIBSC to surpass the efficiency of a single junction cell, optimization of design is required. In this work, a QDIBSC model based on In0.53Ga0.47As quantum dots has been designed and evaluated with respect to dot size and spacing. The impact of carrier lifetime on short-circuit current and open-circuit voltage is studied. The conversion efficiency has been enhanced from 27.1% to 32.62% as compared to a conventional single junction cell.