Schottky Junction Solar Cells Research Articles

Achieving high photovoltaic performance in graphene/AlGaAs/GaAs Schottky junction solar cells by incorporating an InAlGaP hole reflector layer

The purpose of this study is to enhance the efficiency of Graphene/AlGaAs/GaAs Schottky junction solar cells by introducing various Ga-based thin-film materials as a hole reflector (HR) layer. These HR layers are designed to minimize the recombination rate at the back contact and increase the photogeneration rate. In order to investigate the effect of various HR layers on the efficiency of GaAs solar cells, a reference cell was simulated with an efficiency of 14%. The simulation was conducted using the Silvaco ATLAS simulator, under AM1.5G light with a power density of 100 mW/cm2. Subsequently, InAlGaP (InAl0.65Ga0.35P), AlGaAs (Al0.2Ga0.8As), and InGaP (In0.5Ga0.5P) thin films were individually introduced as HR layers to the Graphene/AlGaAs/GaAs single junction solar cell (SJSC). The addition of HR layers to the conventional Graphene/AlGaAs/GaAs Schottky junction solar cell was found to improve the short-circuit current density (Jsc) by enhancing carrier collection and reducing back interface recombination. This approach has also led to a significant increase in external quantum efficiency (EQE) at long wavelengths of around 500–900 nm. The results of this study demonstrate that incorporating an InAlGaP HR layer in the proposed structure due to its wide bandgap, higher photogeneration rate, and higher absorption rate significantly improves the EQE by absorbing longer wavelength photons and increases the efficiency of the solar cell by more than 1.6%.

Remarkable enhancement of graphene/Si Schottky junction solar cell performance with effective chemical treatments

Graphene has been employed in the preparation process of solar cells due to its unique properties. It has been combined with silicon (Si) substrates for preparing the top window structure of a graphene/n-Si Schottky junction solar cell. However, the usage of the mono-graphene layer results in a low fill factor of prepared samples. In addition, the residue of PMMA is one more reason for the low fill factor. Another disadvantage of reported devices is the poor stability of doped devices under ambient conditions. In this work, 2 low-cost and simple chemical treatments are employed to eliminate the residue of PMMA after the wet transfer procedure of graphene. Besides, the fill factor is significantly developed by transferring more than a residue-free graphene layer. An efficiency of 6% is obtained after preparing devices with 3 graphene layers, and the recorded efficiency of 14.2% is attained by the HNO3 dopant. Additionally, doped devices show excessive stability for 2 months under ambient conditions, retaining around 96% of their initial efficiency. We attribute this development to the donation process of electrons achieved by chemical treatments to graphene. This work presents an approach for providing low-cost, simple, high performance and stable graphene/Si Schottky solar cells.

Spray pyrolyzed lead oxide films for Schottky junction solar cells

In this paper, we report the fabrication of Schottky solar cell based on spray pyrolysed lead oxide semiconductor thin films. The non-linear junction were created by using high work function metal alloy of Au–Pd with hydrogen treated undoped and Indium doped lead oxide films. The output of Schottky device with different thickness of absorber layer is presented. The electrical parameters of the device are ascertained from the I–V measurements. The device with 2 μm thickness of absorber layer gives a Voc value of 148 mV and Jsc value of 0.21 mA/cm2. The high ideality factor obtained for all varying thickness is attributed to both the surface states generated under illumination and non-homogeneous interface due to the rough surfaces of spray pyrolysed films. In case of Indium doped lead oxide films, an enhanced Voc value of 570 mV and Jsc of 0.11 mA/cm2 is observed. The pristine films and doped films have been characterized by X-Ray diffraction, Raman spectroscopy and scanning electron microscopy.

Capacitance characterization of graphene/n-Si Schottky junction solar cell with MOS capacitor

Abstract We have demonstrated a simple and accurate method for characterizing the capacitance of Graphene/n-Si Schottky junction solar cells (GSSCs) which embed the metal-oxide-semiconductor (MOS) capacitor. We measured two types of GSSCs, one with thermal annealing treatments (w-a) and one without (wo-a). It was found that the wo-a GSSC exhibits a two-step feature in the phase versus forward bias voltage relationship, which may be attributed to the presence of polymethyl methacrylate residues. By considering the capacitance of the MOS capacitor (Cmos) and its standard deviation, we successfully obtained the capacitance of the Schottky junction (CSch), and evaluated meaningful built-in potentials (Schottky barrier heights) which are 0.51 V (0.78 eV) and 0.47 V (0.75 eV) for the w-a and wo-a GSSCs, respectively, by the Mott–Schottky analysis. We also briefly discuss the relationship between CSch and the Nyquist and Bode plots, finding that the RC time constant decreases due to the subtraction of Cmos.

Long-term stability of graphene/c-Si Schottky-junction solar cells

A long operational lifetime is required for the use of solar cells in real-life photovoltaic applications. The optimization of operational lifetimes is achieved through understanding the inherent degradation phenomena in solar cells. In this study, graphene/Si Schottky-junction solar cells were produced, utilizing liquid-phase-exfoliated graphene as an active surface. The operational and interface stability of these solar cells over a period of 5 years in ambient conditions (following ISOS-D protocols: dark storage/shelf life) was examined, and the origin of their degradation was reported. It was found that the dominant degradation mechanism could be attributed to the degradation of silver contacts. This was indicated by a decrease in shunt resistance, an increase in the ideality factor (due to a higher carrier recombination), and a constant defect density in graphene films for up to 4 years. Measurements across the solar cell's active area during the 5-year period revealed neither significant spatial inhomogeneity, nor shunt channel defects.

Development and Analysis of Graphene-Sheet-Based GaAs Schottky Solar Cell for Enriched Efficiency.

Comparative studies of the 2D numerical modelling and simulation of graphene-based gallium arsenide and silicon Schottky junction solar cell are studied using TCAD tools. The performance of photovoltaic cells was examined while taking parameters, such as substrate thickness, relationship between transmittance and work function of graphene, and n-type doing concentration of substrate semiconduction. The area with the highest efficiency for photogenerated carriers was found to be located near the interface region under light illumination. The significant enhancement of power conversion efficiency was shown in the cell with a thicker carrier absorption Si substrate layer, larger graphene work function, and average doping in a silicon substrate. Thus, for improved cell structure, the maximum JSC = 4.7 mA/cm2, VOC = 0.19 V, and fill factor = 59.73% are found under AM1.5G, exhibiting maximum efficiency of 6.5% (1 sun). The EQE of the cell is well above 60%. This work reports the influence of different substrate thickness, work function, and N-type doping on the efficiency and characteristics of graphene-based Schottky solar cells.

Facile method for fabricating the MXenes-Si based Schottky-junction solar cells

Owing to their tunable properties, 2D materials including MXenes are widely used in different optoelectronic devices due to their inherent conductivity and transparency. MXenes are a class of 2D materials that can be synthesized in the form of a colloidal solution, and these are hydrophilic in nature. Due to their hydrophilicity, MXenes can be easily coated on different substrates, making them suitable in applications like solar cells. Like other materials, MXenes-based solar cell fabrication doesn't require a growth process or a transfer process, hence, solar cells fabrication using MXenes is comparatively a simplified process. In this study, a facile technique was adopted to fabricate the metal-semiconductor (MXenes-Si) junction simply by spin-coating Ti3C2Tx-MXenes on an n-type Si substrate. The electrical properties of the coated MXenes films were investigated at different MXenes to DI water ratios to obtain the optimized concentration for the highest solar cell efficiency. To stabilize the interface between MXenes and Si, Al2O3 was deposited, and the thickness-dependent tunneling effect was also optimized at a 2 nm thick Al2O3 layer. To improve the solar cell efficiency, AuCl3 doping, and texturing of silicon substrate were performed. With these two additional treatments, the efficiency of the solar cell was increased from 2.87% to 3.36%, exhibiting an increase of ∼17% as compared to that without treatment.

Thermal annealing effects on graphene/n-Si Schottky junction solar cell: removal of PMMA residues

Thermal annealing is one of the most effective ways to improve the efficiency of a graphene/n-Si Schottky junction solar cell. Here, its underlying mechanism has been investigated by comparative studies in terms of the removal of polymethyl methacrylate (PMMA) residues, using the J–V characteristics and transient photocurrent and photovoltage measurements. The obtained results have revealed that there are trap states that originate from the PMMA residues and cause the large photocurrent leakage as the intensity of the incident light increases. It is also found that the PMMA residues accelerate deterioration and rapidly invalidate hole doping effects. Such undesirable PMMA residues were effectively removed by the thermal annealing treatments, serving to reduce the photocurrent leakage and increase the stability.

Developed graphene/Si Schottky junction solar cells based on the top-window structure

Developed graphene/Si Schottky junction solar cells based on the top-window structure

Large-area 11.75% efficient vertical graphene nanowalls/textured silicon Schottky junction solar cell based on PEDOT:Nafion doping scheme

Preparing large areas of graphene on textured silicon is necessary for the industrialization of graphene/silicon solar cells. However, many passivation films with insulating properties prepared by the solution method are not applicable for the textured structures as the insulation areas are easily formed at the bottom of the pyramid. In this paper, we prepare large-area vertical graphene nanowalls (VGNWs) on textured c-Si by plasma-enhanced chemical vapor deposition (PECVD) and introduce conductive-passivating poly(3,4-ethylenedioxythiophene) (PEDOT):Nafion composite thin films to modify the textured VGNWs/Si Schottky junction. The formation of insulation areas was avoided. Moreover, the reflectivity was reduced to less than 7% as the superposition of textured structures and PEDOT:Nafion film. After applying an interfacial layer of Al2O3, the cell efficiency was increased to 11.75%, with a large active area of 0.64 cm2. This work will promote the industrialization of VGNWs/Si solar cells.

Current transport characterization and photovoltaic performance of Si nanopencil-based Schottky junction assisted with VOx as a hole-injection layer

Pencil-shaped silicon nanowires (SiNPs) were utilized in Schottky junction solar cells covered by sub-stoichiometric vanadium dioxide (VO2-x) to work as a hole injection layer. The asymmetry of nanopencils is responsible for their many useful properties, such as their ability to absorb and trap light over a wide spectrum. Dark current-voltage (I–V) curves for an Ag/VO2-x/SiNPs/Ti/Ag Schottky junction device were measured and analyzed across a temperature range of 298–358 K. The junction parameters were calculated in terms of thermionic emission theory at different temperatures from the (I–V) curves, including the ideality factor (n) and the barrier height (φb), and were found to be 1.73 and 0.78 eV, respectively, at room temperature. In the forward bias regime, we found that thermionic emissions dominate at low voltages (V ≤ 0.12 V), space-charge-limited current controlled by a single trap state dominates at middle voltages (0.12 < V < 0.3 V), and space-charge-limited current regulated by a distribution of trap levels dominates at high voltages (V ≥ 0.3 V). The (C–V) measurements were used to calculate the built-in potential, which was discovered to be 0.62 eV. Unless encapsulation is provided, PEDOT:PSS/SiNPs hybrid solar cells rapidly degrade under ambient conditions, whereas VO2-x/SiNPs solar cells are far more stable.

High-performance vertical graphene nanowall/silicon Schottky junction solar cells with Nafion doping and plasma etching

In this paper, a solar cell based on the vertical graphene nanowall (VGNW)/silicon Schottky junction is doped by polymeric acid (Nafion) and exhibits a high power-conversion efficiency after Ar plasma etching. It is found that, the Nafion doping scheme effectively increases the WF of VGNW films by ∼0.5 eV, and simultaneously reduces its average reflectance to ∼28%. However, there appears to be a poor-conductive Nafion capping layer on the VGNWs after doping, which severely influences the carriers electrical transportation. When a plasma etching process is introduced, the VGNWs buried in the Nafion polymers are exposed, thus reducing its sheet resistance by ∼20%. The combination of Nafion doping and plasma etching makes the Vbi of the VGNW/n-Si heterojunction greatly improve and exceed 0.6 V, and the FF factor of the VGNW/n-Si solar cells increases from 55.8% to 62.9%. Applying interface passivation and light management, we achieve a significant gain of Jsc and a well-performance VGNW/n-Si Schottky junction solar cell (Voc of 523 mV, FF of 57.1% and Jsc of 30.8 mA/cm2), whose PCEs up to 9.2% (AM 1.5 G). The present device architecture design and optimisation scheme here are envisaged to be potentially valuable for the doping modification of other 3D materials with similar structures.

Developed performance of rGO/p-Si Schottky junction solar cells

Graphene in combination with Si has been extensively used to prepare efficient and stable p-graphene/n-Si Schottky junction solar cells. In contrast, there is a difficulty in including graphene within the fabrication process of efficient and stable n-graphene/p-Si Schottky junction solar cells. The reason for this is that there is a challenge in achieving an effective and stable n-doping process for graphene or rGO due to the ambient environment. In this work, a novel approach is introduced for preparing more efficient, stable, larger and simpler n-rGO/p-Si Schottky junction solar cells. The n-rGO rather than graphene, which has been successfully developed using NH 3 molecules, is included in the fabrication process of n-rGO/p-Si Schottky junction solar cells. Accordingly, the power conversion efficiency of 9.7 was obtained for prepared devices after applying ammonia treatment for 3 h. For the first time, the developed n-rGO layers are also excellently employed to prepare large n-rGO/p-Si Schottky junction solar cells with ideal J-V curves. The improved efficiency of 12.6 % is reached for n-rGO/p-Si Schottky junction solar cells prepared with an active area of 0.6 cm 2 . To improve the stability, devices are coated with PMMA as an encapsulated layer, leading to an improvement in the stability for 2 months in the ambient air. Additionally, a recorded efficiency of 13.8 % is achieved. We attribute this development to the chemisorption of ammonia molecules on rGO, which effectively develops the performance of devices.

Enhanced and Passivated Co-doping Effect of Organic Molecule and Bromine on Graphene/HfO2/Silicon Metal–Insulator–Semiconductor (MIS) Schottky Junction Solar Cells

Graphene (Gr) has shown a significant role in photovoltaic applications due to its exclusive properties. In this study, we established a facile approach to fabricate p-Gr/HfO2/n-silicon, a metal–insulator–semiconductor (MIS) Schottky junction solar cell. Nevertheless, the poor work function of Gr and high-density defect states at the Gr/Si interface obstruct the efficiency of solar cells. To avoid this problem, the optimal thickness of the interfacial layer (HfO2) is employed, which circumvents the recombination process at the Gr/Si interface. Additionally, to boost the Schottky barrier height and Gr’s work function, a combination of p-type co-doping of organic molecule 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) and Br is studied. Therefore, a higher work function aims to encourage the built-in potential, which ultimately improves the open-circuit voltage and current density and deteriorates the series resistance of solar cells. Hence, a unique combination of dopants resulted in improved efficiency of up to 12.31%. Moreover, devices with double layer (MoO3/HfO2) passivation have been enabled to provide outstanding stability for over 180 days. The combined effect of p-type co-doping and double layer passivation developed a solar cell having a significant efficiency of 14.01%. Thus, this work intends to show a promising, high-performance and stable MIS Schottky junction solar cell for massive commercialization of photovoltaic devices.

Design and fabrication of graphene/CdS Schottky junction for photovoltaic solar cell applications

In this report, we study the optimal design and simulation of Schottky junction solar cells consisting of cadmium sulfide (CdS) and graphene layer using Silvaco TCAD Atlas software. During device modeling the thickness of the top layer of graphene as an electrode and the middle semiconducting layer of CdS as an active region is taken as 10 and 70 nm, respectively. Polyethylene terephthalate (PET) is used as the flexible substrate for the study. We also report the fabrication of flexible solar cells on PET substrates composed of CdS and graphene synthesized in-house by solution process. The I-V characteristics have been undertaken in both the simulated and fabricated devices with structure graphene/CdS/PET. Under AM 1.5 G, the fabricated device with the structure graphene/CdS/PET shows an open- circuit voltage (Voc) of 0.163 V, a short circuit current density (Jsc) of 0.00063 A/m2 and a fill factor (FF) of 56.50%. The Ideality factor and reverse saturation current of the device is determined to be 9.6 and 0.063 µA, respectively.

Analytical modeling and design optimization of a graphene/n-GaAs Schottky junction solar cell

A physics-based analytical model is important to understand the working mechanism through process parameters of any innovative material heterostructure. We present an analytical model to calculate the power conversion efficiency of solar cells based on graphene and III-V direct bandgap semiconductors. The model is comprehensively developed by incorporating several current densities obtained from both the generation and recombination processes. Moreover, to obtain a highly efficient Schottky junction solar cell, we propose an optimized structure of graphene/GaAs with lattice-matched passivation and carrier selective layers. The structure has the advantage of surface passivation and photon recycling that reduces interface recombination and ensures more electron–hole pair generation, respectively. It exhibits a theoretical efficiency of >18 % from the analytical model simulation which is later verified by numerical simulation using SCAPS 1D software. The analytical model will provide not only a better understanding of the solar cells’ operation but also a comparative study among them to achieve better efficiency in the future. In addition, the enhanced efficiency of the proposed structure will encourage further research in this field of study.

Near Unity Absorbance and Photovoltaic Properties of TMDC/Gold Heterojunction for Solar Cell Application

In this paper, near unity broadband absorption of Van der Waals semiconductors on a metallic substrate, and their photovoltaic performances in the visible spectrum are simulated. Ultrathin layered semiconductors such as Molybdenum disulfide (MoS2), Tungsten disulfide (WS2), Molybdenum di-selenide (MoSe2), Tungsten di-selenide (WSe2), Molybdenum ditelluride (MoTe2), and Tungsten ditelluride (WTe2) can create strong interference by damping optical mode in their multilayer form and increase light absorption at their heterojunctions with noble metals. From our simulation, it is observed that this absorbance can reach up to 94% when the semiconductors are placed on a gold substrate. The optimum thickness of these semiconductors in their heterostructures with gold is analyzed to create resonant absorption to generate the maximum amount of current density. The power conversion efficiency of the designed Schottky junction solar cells is calculated from their current density vs bias voltage characteristics that ranges from 1.57% to 6.80%. Moreover, the absorption coefficient, dark current characteristic, electric field intensity distribution in the device, and carrier generation rate during light illumination are presented with a view to characterizing and comparing among the parameters of TMDC based nanoscale solar cell.

Photo Effect Studies in Graphene/N-GaAs Schottky Junction Using NEGF Method for Photovoltaic Application

In this paper, we present the photovoltaic characteristics of nanoscale Schottky junction solar cell consisting of graphene and GaAs using numerical simulation based on non-equilibrium Green’s function formalism. In our model, light-matter interaction is formulated by the coupling and scattering self-energy matrices whereas heterostructure is designed with a Hamiltonian matrix. An efficiency of 2.36% is obtained for monolayer graphene on GaAs; the efficiency is later enhanced to 5.40% by increasing both the number of graphene layers and the doping concentration of GaAs. The parameters to calculate power conversion efficiency, series and shunt resistances are extracted from the J-V characteristic. The I-V characteristic is also numerically simulated to extract reverse saturation current, ideality factor, and rectification ratio. Moreover, the power density is calculated for the optimized structure; the maximum power density of 7.46 mW/cm2 is obtained for four layers of graphene and a doping concentration of 1017/cm3 in GaAs.

Enhanced Efficiency of Graphene-Silicon Schottky Junction Solar Cell through Pyramid Arrays Texturation

Graphene/silicon (Gr/Si) Schottky junction solar cells have attracted extensive research interest due to their simple structure and potential low-cost. Surface texturing is an important part of high-efficiency solar cells. In this paper, the effects of TMAH concentration, IPA concentration and etching time on the structure and anti-reflection ability of silicon pyramid array (SiPa) were systematically studied to obtain uniform and reliable pyramid array. Under the optimized conditions, a large scale SiPa with uniform size distribution was obtained and applied to Gr/Si solar cells. The results show that the TMAH etched SiPa has a better Schottky junction contact between graphene and the SiPa surface, and the SiPa can further improves the ability of collecting photogenerated carriers. Compared with Gr/Si solar cells, the power conversion efficiency (PCE) of Gr/SiPa device is 1.66 times higher than that of Gr/Si solar cells. Finally, Gr/SiPa devices with PCE of 5.67% is successfully obtained by HNO3 doping. This work proposes a new strategy for TMAH etching SiPa to improve the performance of Gr/Si solar cells.

Enhancement of Schottky Junction Silicon Solar Cell with CdSe/ZnS Quantum Dots Decorated Metal Nanostructures

Recently, in the solar energy society, several key technologies have been reported to meet a grid parity, such as cost-efficient materials, simple processes, and designs. Among them, the assistive plasmonic of metal nanoparticles (MNPs) integrating with the downshifting on luminescent materials attracts much attention. Hereby, Si-based Schottky junction solar cells are fabricated and examined to enhance the performance. CdSe/ZnS quantum dots (QDs) with different gold nanoparticles (Au NPs) sizes were incorporated on a Si light absorbing layer. Due to the light scattering effect from plasmonic resonance, the sole Au NPs layer results in the overall enhancement of Si solar cell’s efficiency in the visible spectrum. However, the back-scattering and high reflectance of Au NPs lead to efficiency loss in the UV region. Therefore, the QDs layer acting as a luminescent downshifter is deployed for further efficiency enhancement. The QDs layer absorbs high-energy photons and re-emits lower energy photons in 528 nm of wavelength. Such a downshift layer can enhance the overall efficiency of Si solar cells due to poor intrinsic spectral response in the UV region. The optical properties of Au NPs and CdSe QDs, along with the electrical properties of solar cells in combination with Au/QD layers, are studied in depth. Moreover, the influence of Au NPs size on the solar cell performance has been investigated. Upon decreasing the diameters of Au NPs, the blueshift of absorbance has been observed, cooperating with QDs, which leads to the improvement of the quantum efficiency in the broadband of the solar spectrum.