Intrinsic Thin Layer Research Articles

Simulation and Analysis of Losses by Degradation in Photovoltaic Energy Production System

Currently several technologies are being developed to produce electricity from renewable sources, and the degrees of maturity, performance and lifetime are very different from one technology to another. This work presents a study by a simulation and analysis for clarity the effect of aging of a photovoltaic module associated with an energy production system of renewable origin installed in a desert environment. The PV array has a nominal power of 9,2KWp, and the photovoltaic module used in this study is heterojunction with intrinsic thin layer technology of 230WP. During this work, we obtained the system production is 17131 KWh/year, the producible is 1862 KWh/KWp/year, and the normalized production is 5,10 KWh/KWp/day, with the losses of the system is 0,16KWh/KWp/day. The performance ratio of our simulated system is about 0,822, and the collection loss of the photovoltaic field is LC = 0,94KWh/KWP/day, with loss system is LS = 0,16 KWh/KWP/day, and the aging rate of photovoltaic module estimated by simulation around the 14% for 25 years of electrical production in a desert environment.

Electrical and Optical Characterization of Non-Hydrogenated a-Si/c-Si Heterojunction Solar Cells

This work deals with the performance of a heterojunction with intrinsic thin layer solar cell by sputtering silicon on p-type crystalline silicon substrate in argon ambient without hydrogen addition. This first effort was an attempt to use cost-effective means to convert light into electricity and to find fabrication processes which use fewer and cheaper materials for the fabrication of solar cells. Since transport mechanisms of amorphous silicon/crystalline silicon heterojunctions are still under investigation, the aim is to examine the behavior of the fabricated samples under electrical and optical constraints. Initial cell characterization includes electrical behavior via current-voltage characteristics and optical investigation via reflectance and absorptance measurements. Results are analyzed in a tentative to follow the absorption, generation and collection processes in the fabricated cell. The heterojunction interface is found to be a limiting factor in the cell performance. Under sun illumination, the open circuit voltage was 140 mV, the short circuit current was of 6 µA and the fill factor was of 42.56 %. Dark current-voltage characteristics indicated a tunneling and/or recombination carrier transport mechanism, while aborptance/reflectance measurements showed a generation process occurring in most in the crystalline silicon-side of the amorphous/crystalline silicon heterojunction. A carrier collection limitation is a very probable origin of the decreased cell generated current.

Estimation of module temperature for water-based photovoltaic systems

Estimation of module temperature is important for the assessment of performance and reliability of photovoltaic (PV) modules. The objective of the present work is to develop a simple model for estimation of module temperature of water-based PV systems. In this paper, a new approach has been proposed to incorporate the effect of water on PV module temperature. PV modules experience differential heat exchange from their front and rear sides under the influence of water. Therefore, in the proposed approach, separate thermal loss coefficients have been calculated for the front and rear sides of PV modules. The experimentally measured data of a complete year has been utilized to determine the thermal loss coefficients of front and rear sides of PV modules. These coefficients have been used along with PV module technology parameters for predicting module temperature. The ratio of front and rear side thermal loss coefficient of hetro-junction with intrinsic thin layer (HIT), multi-crysalline Silicon (mc-Si), and Cadmium Telluride (CdTe) PV technologies is found to be 0.537, 0.556, and 0.363, respectively. The developed model has been validated using an experimental setup comprising of three different PV module technologies. The mean bias error and root mean square error for the developed model have been found to be less than 0.5 °C and approximately 3 °C, respectively. This shows that the developed model is accurate enough and consistent for temperature estimation of different PV module technologies on water bodies.

Numerical Simulation for Optimization of Ultra-thin n-type AZO and TiO2 Based Textured p-type c-Si Heterojunction Solar Cells

A maximum efficiency of 17 % for ultra-thin n-type AZO layer and 17.5 % for ultra-thin n-type TiO2 layer based silicon heterojunction solar cell is reported by optimizing its properties which is much higher than practically obtained efficiency signifying a lot of improvements can be performed to improve efficiency of TiO2/Si and AZO/Si heterojunction solar cell. AZO layer and TiO2 layer is used as n-type emitter layer and crystalline silicon wafer is used as p-type (p-cSi) layer for modelling AZO/Si and TiO2/Si heterojunctions solar cell respectively using AFORS HET automat simulation software. Various parameters like thickness of AZO, TiO2 layer, p-cSi layer, doping concentration of donors (Nd) and effective conduction band density (Nc) are optimized. Finally, texturing at different angle is studied and maximum efficiency is reported at 70 μm thick p-type crystalline Silicon (p-cSi) wafer, that can be very helpful for manufacturing low cost HJ solar cells at industrial scale because of thin wafer and removal of additional processing setup required for deposition of amorphous silicon i-layer. Utilization of TiO2 and Aluminium doped Zinc Oxide as n-type layer and p-cSi as p-type layer can help in producing low cost and efficient heterojunction (HJ) than compared to HJ with intrinsic thin layer HIT solar cells.

Simulation of a Charged Al2O3 Film as an Assisting Passivation Layer for a-Si Passivated Contact P-Type Silicon Solar Cells

In this paper, a charged Al2O3 tunneling film as an assisting for amorphous Si (a-Si) passivated contact layer is proposed and theoretically simulated for its potential application in improving a-Si passivated contact p-type (a-PC-p) solar cell. The concept is based on an Ag/n+ c-Si/p c-Si/Al2O3/p+ a-Si/Al structure. The key feature is the introduction of a charged Al2O3 layer, which facilitates the tunneling of holes through an Al2O3 insulator layer accompanied by the reduction of interface defect density (Dit). The negative charge in the Al2O3 layer makes the energy band of p-type c-Si bend upward, realizing the accumulation of holes and repelling of electrons at the c-Si/a-Si interface simultaneously. The influence of interface negative charges (Qit) between a-Si and c-Si, Al2O3 thickness, Al2O3 bandgap, interface defect density (Dit) at the a-Si/c-Si interface are systematically investigated on the output parameters of a-PC-p cells. Inserting a charged Al2O3 film between the c-Si/a-Si interface, a + 4.2% relative efficiency gain is predicted theoretically compared with the a-PC-p cells without the Al2O3 layer. Subsequently, the device performance under various temperatures is simulated, and the insertion of a charged Al2O3 layer obviously decreases the Pmax temperature coefficient from −0.336% /°C to −0.247% /°C, which is analogous to that of Heterojunction with Intrinsic Thin layer (HIT) solar cell. The above results demonstrate a better temperature response for a-PC-p cells with a charged Al2O3 layer, paving a road for its potential application in high-efficiency and high thermal stability a-PC-p solar cells.

Mathematical Modelling of a Novel Hetero-junction Dual SIS ZnO-Si-SnO Solar Cell

For the last few decades scientists across the world have achieved significant improvement in performance of conventional silicon p-n junction solar cell. Sophisticated high temperature doping technology is unavoidable in the fabrication of these conventional solar cells. Back in 1970s scientists proposed an alternative solar cell technology with Schottky barrier which can cut down the burden on thermal budget of manufacturing process. Later the metal-semiconductor Schottky barrier further modified with hetero junction semiconductor-semiconductor solar cells. A thin intrinsic layer sandwiched between semiconductor-semiconductor junctions can repair the junction defect efficiently. These SIS solar cells became popular for its low thermal budget and considerable efficiency. In this paper we have tried to propose a mathematical model of a novel dual side SIS solar cell which is basically a multi junction solar cell. We have introduced a third semiconductor layer (SnO) at the back side of the cell which can provide an inversion layer much similar to PERT solar cell. This structure is first of its kind and thus a theoretical analysis is required before implementation. We have studied the effect of this back field on the performance of the cell and propose a mathematical model based on reciprocity theorem of charge collection. The efficiency of conventional ZnO-pSi SIS solar cell was computed ~5.2% while the back SnO p+ layer is expected to enhance the efficiency up to ~7.9% according to our mathematical model. We have concluded with significant mathematical justification to implement this structure with proposed electro-chemical experiments.

Simulation and Optimization of Back Surface Field for Efficient HIT Solar Cells

We investigate an appropriate material for the optimisation of Back Surface Field (BSF) layer in Heterojunction with Intrinsic thin layer (HIT) solar cells: ITO/p-a-Si:H/i-a-Si:H/n-c-Si/BSF/Ag. The obtained results show that it is important to choose hydrogenated amorphous silicon to create the BSF layer instead of crystalline silicon as in the case for conventional HIT solar cells. The use of hydrogenated amorphous silicon creates a significant band discontinuity at the valence band due to the presence of the heterojunction at the interface n-c-Si/n++-a-Si:H. We also show that increasing the BSF layer thickness degrades the solar cell J-V characteristic due to the low diffusion length and lifetime of the minority carriers and also because of the increase of the recombination rate in this heavily doped layer. The global device optimization was performed with SCAPS–1D software under STC conditions and the results show that a considerable efficiency of 27.44 % can be achieved.

Surface Passivation Studies of n-type Crystalline Silicon for HIT Solar Cells

Surface passivation of n-type Crystalline Silicon wafer using thin dielectric films is an important and major factor in improving photovoltaic performance of HIT solar cells. In this study, Numerical simulation was carried out by using AFORS-HET simulation software in which energy band diagram with and without surface passivation (a-Si:H(i)) was investigated and the highest conduction band offset obtained on n type c-Si wafer is 0.85 eV which is comparatively higher than p-type c-Si wafer which was reported between 0.1 and 0.15 eV. Performance of HIT solar cell with passivation layer is simulated and obtained efficiency of 12.9% by incorporating actual conditions to compare with experimentally obtained data. It has been understood that applying an effective dielectric passivation of silicon surface resulted with high open circuit voltage (Voc) and low surface recombination lead to an increase of cell efficiency by 1.1% (from 11.8 to 12.9%). Also, the simulated results shows that to obtain good conversion efficiency Defect density of interface (Dit) should be lower than 1x1011 cm−2eV−1. Validation of the simulation results is done by conducting PECVD experiments for optimizing the amorphous silicon passivation to a layer thickness down to 15 nm. HIT Solar cells have been developed, using the optimum layer of passivation, and their performance have been studied. An improvement in the minority charge carrier lifetime of ~53 µs (from 215 to 268 μs) and on the other hand reduction in the surface recombination velocity of ~ 12.9 cm/s (from 65.11 cm/s down to 52.23 cm/s) has been achieved through passivation which effectively increased the open circuit voltage (Voc) from 0.690 to 0.705 V. In this preliminary study, a conversion efficiency of 11.3% of heterojunction with intrinsic thin layer (HIT) solar cell on 10 mm × 10 mm n-c-Si wafer has been obtained.

Grating-enabled high-speed high-efficiency surface-illuminated silicon photodiodes.

High-speed, high-efficiency silicon photodetectors play important roles in the optical communication links that are used increasingly in data centers to handle the increasing volumes of data traffic and higher bandwidths required as use of big data and cloud computing continues to grow exponentially. Monolithic integration of the optical components with signal processing electronics on a single silicon chip is of paramount importance in the drive to reduce costs and improve performance. Here we report grating-enhanced light absorption in a silicon photodiode. The absorption efficiency is determined theoretically to be as high as 77% at 850 nm for the optimal structure, which has a thin intrinsic absorption layer with a thickness of 220 nm. The fabricated devices demonstrate a high bandwidth of 11.3 GHz and improved radio-frequency output power of more than 14 dB, thus making them suitable for use in data center optical communications.

Comparative degradation analysis of different photovoltaic technologies on experimentally simulated water bodies and estimation of evaporation loss reduction

AbstractDegradation of photovoltaic (PV) systems on water bodies can be matter of serious concern due to high humid environmental conditions above water surface as compared with land surface. The primary objective of this study is to assess the reliability of various PV technologies for megawatt‐scale installations by analyzing their degradation on water bodies. An experimental study has been performed for 13 months on three commercially available PV technologies, namely, multicrystalline‐Si (m‐Si), heterojunction intrinsic thin layer (HIT), and cadmium telluride (CdTe). Degradation of these PV technologies on water and comparison of their degradation with respective land‐mounted PV technologies have been presented. Various approaches have been implemented for degradation analysis. The degradation in electrical parameters of all PV modules has been measured. Also, a mathematical PV model has been developed to analyze the internal parameters degradation in different PV technologies. Moreover, thermal imaging has been conducted to distinguish various defects in all PV modules. Evaporation reduction is a significant aspect of water‐mounted PV systems, and thus, analytical model to estimate evaporation has been developed and experimentally validated in this study. The HIT PV technology is observed to be degrading almost at the same rate of about 0.50% on both water and land surfaces, whereas degradation of water‐mounted m‐Si module has been found 1.32% which is significantly higher than the corresponding land‐mounted module which has degradation of 0.93%. Degradation in CdTe modules is 1.68% on water, which is marginally higher than corresponding land‐based module that has degradation of 1.41%.

Characterization of the Laser Scribing Process of HIT Cells for a Photovoltaic Shingled Module

Shingled string technology can be used to maximize the output power of photovoltaic modules. The maximum power (Pmax) of a shingled photovoltaic module can be increased by using a bifacial heterojunction with an intrinsic thin layer (HIT) of cells. To fabricate the shingled strings for a high power module, we first cut 6-inch solar cells by laser scribing while minimizing cutting loss. Unlike standard crystalline silicon (c-Si) solar cells, the structure of bifacial HIT solar cells is weak under thermal effect, so an optimal scribing condition had to be found. After laser scribing processes had been optimized, Pmax was increased by 0.02W for each separated solar cells when we using an ultraviolet (UV) laser compared to the green laser, and a UV cut shingled string of HIT cell was demonstrated for the first time.

A Method for Calculating Operating Characteristics of Silicon Heterojunction Solar Cells with Arbitrary Parameters of Crystalline Substrates

Specific features of the current processes in silicon heterojunction with intrinsic thin layer solar cells have been investigated. The proposed model takes into account the ambipolar motion of carriers and allows one to calculate the operating characteristics at an arbitrary ratio of the diffusion length and the crystalline-substrate thickness. A numerical method for estimating the recombination-loss rate on silicon wafer surfaces based on the comparative analysis of the experimental values of short-circuit current and open-circuit voltage is described.

Performance enhancement of ultrathin graded Cu(InGa)Se2 solar cells through modification of the basic structure and adding antireflective layers

Traditional Cu ( InGa ) Se2 (CIGS) solar cells consist of an Mo bottom contact, p-type CIGS absorber layer, n-type CdS buffer layer, and ZnO window layer including a very thin intrinsic ZnO layer topped with an Al-doped ZnO transparent conducting oxide layer that was simulated by an Silvaco technology computer aided design simulator. The thickness of the layers and other parameters were limited to the values reported in the literature. The simulator was examined to affirm its functionality, and a step-by-step method was applied to optimize the baseline structure. The first modification was the substitution of the conventional CdS buffer layer with a nontoxic n-type ZnO buffer layer. The substituted ZnO buffer layer showed an effective band alignment and led to a remarkable improvement in cell performance. The second modification was the inclusion of different antireflective coatings, such as Al2O3, MgO, SnO2, and CdO, to enhance light trapping. Among them, CdO caused the highest efficiency. The optimization process was followed by replacing a very-thin (750 nm) CIGS layer containing three sublayers with dual-graded Ga contents. A trapezoidal gradient profile was tested and showed a significantly increased internal electric field, which assisted in raising the efficiency of the device. The last simulation concluded that the efficiency of a CIGS solar cell was 19.21% and the efficiency related to the baseline structure was enhanced by 36.24%.

Low temperature defect passivation technology for semiconductor electronic devices—supercritical fluids treatment process

Currently, defects existing in materials and at the interface are the main bottlenecks limiting the manufacture of high-performance electron devices, especially semiconductor devices where the performance and reliability are affected by these defects. Therefore, high temperature annealing (HTA) is often applied to passivate defects, though it raises additional issues in the device fabrication process, such as heat budget and impurity diffusion. In this article, we propose a passivation technique induced by a supercritical fluid (SCF) treatment at relative low temperatures and test it for use in various devices. The SCF treatment is equipped with both high permeability and solubility to introduce reactive substances which act to passivate defects and further enhance device performance without altering the device material or making major changes to the fabrication process. The experimental results prove that this technique can be applied to the AlGaN-based ultraviolet C light-emitting diode to increase the band-to-band emission spectrum of 280 nm, as compared with the 360 nm emission spectrum of defects. The electrical characteristics of the GaN-based high electron mobility transistor including on/off currents, trans-conductance (Gm), and current collapse were also improved. Such a SCF treatment can also be applied to Si-based fin field effect transistors to increase the Gm and mobility because of reduction of defect concentration. This SCF treatment was also applied to a current-production heterojunction with intrinsic thin layer solar cell to improve the efficiency from 18.2% to 19.5%. Using this SCF treatment on InGaZnO thin film transistors results in effective suppression of the VTH shift, which proves the defects in the gate insulator have been eliminated. The SCF treatment has also been applied to a SnO2 gas sensor to increase the selectivity and endurance to humidity because of the passivation of vacancies. These all confirm that this SCF treatment's passivation capability can be applied to various electron devices. In addition, this SCF treatment has the advantages of being performed at low-temperature in a non-destructive process in a batch treatment with high selectivity, which provides the semiconductor industry a method to solve the manufacturing bottleneck in advanced electron devices.

Investigation of a dual MOSCAP TFET with improved vertical tunneling and its near-infrared sensing application

In this work, a δ-doped dual MOS-capacitor (MOSCAP) (D-MOS) tunnel field effect transistor is proposed and investigated. The investigation has been carried out by varying the mole fraction of the SiGe δ-layer as well as by optimizing device dimensions like the effective oxide thickness, elevated channel thickness and epi-layer (thin intrinsic layer of the MOSCAP region) length and thickness. The optimized proposed device offers an ON current of 6.91 × 106 A µm-1, ION/IOFF of 4.83 × 108, average sub-threshold swing of 18.67 mV dec−1 and a maximum cut-off frequency of 1.28 × 109 Hz. Furthermore, the application of the proposed device as a near-infrared optical sensor is studied using a photosensitive gate. It is observed that the device can sense closely spaced spectral wavelengths (∼100 nm) in the near-infrared region of the spectrum (1–0.7 µm) at low intensity of illumination (<1 W cm−2). The peak spectral sensitivities of 4.67 × 103, 3.3 × 103 and 9.77 × 102 for the wavelength pairs (0.8 µm–0.7 µm), (0.9 µm–0.8 µm) and (1 µm–0.9 µm), respectively, are observed making it a highly sensitive optical sensor.

Optimisation of emitter properties for silicon heterojunction solar cell ITO/p-a-Si:H/i-a-Si:H/n-c-Si/BSF/Al

In this study, the performance of silicon Heterojunction with Intrinsic Thin layer (HIT) solar cell was numerically simulated and optimized by Amorphous Semiconductor Device Modelling Program (ASDMP). In this work we have not only studied the influence of physical and geometric parameters of the emitter on the performance of the cell, we have also studied the conduction and recombination phenomena which are the basis of the improvement / deterioration of the studied solar cell.we were able to conclude that a compromise must be made in the choice of the thickness of the emitter: Not too thin to have a sufficient electric field at the junction p-a-Si: H / n-c-Si, and not too thick, so that a maximum of photons are transmitted to the active layer, and so that the diffusion length of the charge carriers is at least equal to the thickness of the emitter. A thickness of the p-Si: H layer of 155A° has achieved the best values of the cell parameters, with an efficiency of 18.25 %.The performance of the HIT studied cell is improved by increasing the doping density of the emitter layer made of p-type hydrogenated amorphous silicon (p-a-Si: H). Despite the deterioration of the material by the doping, the rate of recombination decreases on the active layer (n-c-Si) because of the higher electric field strength. We achieved an efficiency of 19.8 % by optimizing both of gap energy and doping density.

Numerical analysis of metal-semiconductor junctions ITO/p-a-Si:H and n-c-Si/Al on silicon heterojunction solar cells

The device used in this work consists of an amorphous n-type Heterojunction with Intrinsic Thin layers (HIT) solar cell with the structure: Indium Tin Oxide (ITO)/hydrogenated p-doped amorphous silicon (p-a-Si:H)/hydrogenated intrinsic polymorphous silicon (i-pm-Si:H)/n-doped crystalline silicon (n-c-Si)/Aluminium (Al). In this article we have studied the metal-semiconductor junctions at the front and back contacts (ITO/p-a-Si: H and n-c-Si/Al) on amorphous n-HIT solar cells. It is shown that an increase of the contact barrier height ϕb0 at the front interface ITO/p-a-Si:H leads to an increase of the efficiency of amorphous n-HIT solar cells, while the performances of the studied solar cells fall when the contact barrier height ϕbL at the back interface n-c-Si/Al is increased. Indeed, we thus improve the efficiency of the studied cell by choosing a TCO with high work function. Zinc oxide (ZnO) with a working function of 5.2 eV could be the best TCO for this type of solar cells. At the rear of the device, Aluminum is a good candidate for the elaboration of the back contact, because it has a work function equal to 4.06 eV considered one of the smallest compared to other metals.

26.7% Efficient 4-Terminal Perovskite–Silicon Tandem Solar Cell Composed of a High-Performance Semitransparent Perovskite Cell and a Doped Poly-Si/SiOxPassivating Contact Silicon Cell

The rapid rise in single-junction perovskite solar cell (PSC) efficiencies, tunable bandgap, and low-cost solution processability make PSCs an attractive candidate for tandems with Si bottom cells. However, the challenge is to fabricate a high-performance semitransparent perovskite top cell in combination with an appropriate silicon bottom cell with high response to long wavelength photons that are filtered through the perovskite top cell. Currently, semitransparent perovskite cells show much lower performance compared with their opaque counterparts, while high-performance silicon bottom cells, such as heterojunction with intrinsic thin layer and interdigitated back contact, may be too expensive to meet the cost and efficiency targets for commercial viability. Here, we demonstrate a 26.7% perovskite-Si four terminal (4T) tandem cell comprising a highly efficient 17.8% CsFAMAPbIBr semitransparent, 1.63-eV bandgap perovskite top cell, and a ≥22% efficiency n-type Si bottom cell fabricated with a conventional boron diffused emitter on the front and carrier selective n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> poly-Si/SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> passivated contact on the rear. This is among the highest efficiency perovskite/Si 4T tandems published to date and represents the first report of the use of the high temperature-resistant single side n-tunnel oxide passivated contact Si cell in a 4T configuration.

1.73 eV AlGaAs/InGaP heterojunction solar cell grown by MBE with 18.7% efficiency

AbstractWe report on AlGaAs‐based heterojunction solar cells grown by solid source molecular beam epitaxy (MBE). We investigate InGaP and AlGaAs material quality and we demonstrate significant efficiency improvements by combining the best of each alloy: a thick p‐AlGaAs base with tunable bandgap, and a thin 50 nm n‐InGaP emitter separated by a thin intrinsic AlGaAs layer. We report a certified solar cell conversion efficiency of 18.7% with a 2‐μm‐thick AlGaAs layer and a bandgap of 1.73 eV, suitable for high efficiency Si‐based tandem devices.

Operational Performance and Degradation Influenced Life Cycle Environmental–Economic Metrics of mc-Si, a-Si and HIT Photovoltaic Arrays in Hot Semi-arid Climates

Life cycle metrics evolution specific to the climate zone of photovoltaic (PV) operation would give detailed insights on the environmental and economic performance. At present, vast literature is available on the PV life cycle metrics where only the output energies ignoring the degradation rate (DR) influence. In this study, the environ-economic analysis of three PV technologies, namely, multi-crystalline silicon (mc-Si), amorphous silicon (a-Si) and hetero-junction with an intrinsic thin layer (HIT) have been carried out in identical environmental conditions. The energy performance parameters and the DR rate of three PV technologies are evaluated based on the monitored real time data from the installation site in hot semi-arid climates. The assessment demonstrates that the HIT PV module technology exhibits more suitable results compared to mc-Si and a-Si PV systems in hot semi-arid climatic conditions of India. Moreover, energy metrices which includes energy payback time (EPBT), energy production factor (EPF) and life cycle conversion efficiency (LCCE) of the HIT technologies are found to be 1.0, 24.93 and 0.15 years, respectively. HIT PV system has higher potential to mitigate the CO2 and carbon credit earned compared to mc-Si and a-Si PV system under hot semi-arid climate. However, the annualized uniform cost (UAC) for mc-Si (3.60 Rs/kWh) and a-Si (3.40 Rs/kWh) are more admissible in relation to the HIT (6.63 Rs/kWh) PV module type. We conclude that the approach of considering DR influenced life cycle metrics over the traditional approach can support to identify suitable locations for specific PV technology.