Junction Amorphous Silicon Solar Cells Research Articles

Triple Radial Junction Hydrogenated Amorphous Silicon Solar Cells with >2 V Open‐Circuit Voltage

Amorphous Silicon Solar Cells In article number 2200248, Pere Roca i Cabarrocas and co-workers demonstrated triple junction amorphous silicon solar cells grown around silicon nanowires, providing the elevated voltage (>2V) and enhanced effective surface area necessary for applications such as water splitting. The semi-randomly dispersed nanowires are grown in the same vacuum step as the solar cells and without lithography, making this technology a good candidate for low-cost applications.

Approximation of photovoltaic characteristics curves using Bézier Curve

Accuracy of solar cell model parameters is now a requirement for the manufacturing of appropriate photovoltaic models. Consequently, the methodologies of the parameters had already attracted immense interest among researchers over the years. This paper deals about the approximation of the characteristics curves of a solar cell using the Bézier curve method. This technique is selected to overcome the problems of the non-linearity, complexity, multivariate and multimodal of the characteristic's curves. The Bézier curves method is a parametric curve used throughout computer graphics and related disciplines. It is a robust methodology for constructing free-form curves, surfaces, shape design, and geometric representation of various products. Six different cases are carried out to test the validity of the proposed method, they are: (i) organic flexible dual junction amorphous silicon solar cell, (ii) silicon solar cell, (iii) Schutten Solar STP6-120/36 polycrystalline photovoltaic module, (iv) Schutten Solar STM6-40/36 monocrystalline photovoltaic module, (v) Photowatt-PWP 201 polycrystalline photovoltaic module and (vi) 230-W multi-silicon photovoltaic module under partial shading conditions. The technique is implemented and adapted by the mean of the De Casteljo algorithm to optimize the control points and minimize the distance between the experimental and calculated points. It is based on subdividing the curve into various segments and controlled by control points using the De Casteljo algorithm to minimize the distance between the experimental and theoretical points. The performance of the approximated characteristics curves is compared with experimental data as well as recent algorithms and techniques from the literature. For more validity, statistical error metrics from literature are computed and compared to ensure the accuracy of the approximated results and the performance of the proposed method. For instance, the comparison is carried out by resorting to the Individual Absolute Error (IAE) and the Relative Error (RE). Further, the Bias metrics and accuracy are calculated using the Autocorrelation Function (ACF), Tracking Signal (TS), and Normalized Forecast Metric (NFM). The proposed method provides a low error for the six case studies and better than that obtained by the other algorithms.

P+aSixC1-x: H/i-aSi:H/n+aSi1-xGex:H graded band gap single junction solar cell with composition graded amorphous silicon carbon alloy as window layer

The work explores the conduct of composition graded amorphous silicon carbon alloy (aSixC1-x: H) as window layer on graded band gap amorphous silicon (p+aSixC1-x: H/i-aSi:H/n+aSi1-xGe x:H) solar cells, for the first time. The working principle of the proposed structure is interpreted with the aid of energy band diagram. Experimentally validated parameters were adopted for the simulation of the proposed structure. It is observed that the proposed structure is efficient in delivering conversion efficiency (η) of 15.39% at 300 K on reducing its window layer thickness to 5 nm, which is commensurate to other announced amorphous silicon solar cells. The momentous cutback in thickness of one of the active layer leads to lesser material demand and diminishes the overall manufacturing cost. Further, the effect of variation in temperature on the proposed structure has been evaluated and observed that the performance remain almost unaltered. Furthermore, the proposed solar cell structure is compared with our previous work and state of art of single junction amorphous silicon solar cell structures.

Analysis, optimisation and experimental validation of [formula omitted]aSi:H/i-aSi:H/p+aSiGe:H graded band gap single junction solar cell

In this paper, we present a single junction graded band gap thin film solar cell using heavily phosphorous doped amorphous silicon, intrinsic amorphous silicon and heavily boron doped amorphous silicon germanium. The first part of the work presents a rigorous analysis of J-V characteristics of recommended photovoltaic structure under short circuit (SC), open circuit (OC), dark and AM 1.5G illumination standard. Further, optimisation of thickness of active layers of the suggested n+ aSi:H/i aSi:H/p+aSiGe:H solar cell structure is done using SCAPS1D solar simulator. The active layer thickness of the proposed solar cell is 430 nm only. Low active layer thickness and absence of multiple junctions reduces the material requirement, complexity and cost of the proposed solar cell. Furthermore, fabrication of individual layers and overall summary of their characterisation have been done. Finally, the proposed structure has been fabricated and validated its J-V characteristics. The fabricated solar cell has short circuit current density (Jsc) of 11.67 mA/cm2, open circuit voltage (Voc) of 1.18 V, fill factor (FF) of 0.857 and conversion efficiency (η) of 11.80% which is on par with other announced single junction amorphous silicon solar cells. Here, we are reporting a single junction graded band gap solar cell using combination of aSi:H and aSiGe:H alloys with varying doping levels for the first time, which is better in conversion efficiency while compact and light.

Performance evaluation of composition graded layer of aSi1-xGex: H in n+aSi:H/i-aSi:H/p+aSi1-xGex:H graded band gap single junction solar cells

The work investigates the role of composition grading of amorphous silicon germanium alloy on single junction graded band gap amorphous silicon solar cells, for the first time. The fabrication and optical characterization of composition graded aSi1-xGex: H alloy by varying the gas flow rate of germane (GeH4) are presented. We propose the composition graded p+aSi1−xGex: H layer to be considered as one of the active layers in amorphous silicon based solar cells. The principle of operation of the solar cell is illustrated with the energy band diagram of proposed n+aSi:H/i-aSi:H/p+aSi1-xGex:H solar cell structure. Further, the behavior of the structure is evaluated through simulation in terms of proposed layer thickness variation and temperature variation. It is observed that the proposed structure is capable of delivering an open circuit voltage (Voc), short circuit current density (Jsc), Fill Factor (FF) and conversion efficiency (η) of 1.1 V, 15.56 mA/cm2, 0.885 and 15.19% respectively, which is at par with any other single junction amorphous silicon solar cells. The cell performance parameters were compared with related state of the art as well as our previous works. The performance parameters of proposed structure show that it is better to use a single composition graded layer instead of using a number of non-graded composition layers in photovoltaic structures, which reduces complexity and cost of fabrication.

Sacrificial layer assisted front textured glass substrate with improved light management in thin film silicon solar cells

The surface morphology of the front transparent conductive oxide (TCO) films plays a vital role in amorphous silicon thin film solar cells due to their high transparency, conductivity and excellent light scattering properties. Low haze value (5.98%) and surface r.m.s roughness (3.07 nm) are the major issues of aluminium doped zinc oxide (AZO) films to be used as the front TCO due to ineffective scattering of light. Wet chemical texturization of glass substrates using aluminium doped zinc oxide (AZO) as the sacrificial layer was developed in this work to counter those issues. 45% haze and 134 nm surface r.m.s roughness were achieved in AZO coated textured glass. The etched glass/AZO samples presented a much stronger light-scattering capability than the flat glass/AZO and they showed equivalent electrical properties with flat glass/AZO. Single junction amorphous silicon solar cells were fabricated on both flat and textured AZO coated glass substrate and an increment of short circuit current of ~ 12.96% was achieved due to scattering of light from the textured substrate into the cell.

Simulation and analysis on device parameter variations of single junction hydrogenated amorphous silicon solar cell

A novel single junction amorphous silicon solar cell is investigated by numerical simulation tool AFORS-HET to understand the influence of various parameters such as bandgap, different layer thickness, doping concentrations of P and N layers, transparent conducting oxides as textured and plane surfaces with graded structures on efficiency of solar cell. The trade-off between input parameters were examined in terms of short circuit current density (Jsc), open circuit voltage (Voc), Fill Factor (FF) and efficiency (η) as a function of different structural variations for efficiency enhancement. The systematic approach from front to back layer is investigated and the output parameters are tabulated with varied layer configurations to get clear understanding on the relative improvements over the input parameter variations. Simulated results show that maximum of 8.04% and 11.03% efficiency is seen by graded and textured structures respectively compared to maximum 3.46% efficiency of standard p-i-n structure. A structure with combination of graded and textured layers could provide maximum efficiency up to 19.08% is presented.

Review of Maximum Power Point Tracking Control of Photovoltaic Systems in Case of Uniform & Non-uniform Irradiance Conditions

It is crucial to improve the photovoltaic (PV) system efficiency and to develop the reliability of PV generation control systems. One of the approaches to increase the efficiency of PV power generation system is to operate the PV systems optimally at the maximum power point. However, the PV system can be optimally operated only at a specific output voltage; otherwise the output power fluctuates under intermittent weather conditions. In addition, it is very difficult to test the performance of PV systems controller under the same weather condition during the development process where the field testing is costly and time consuming. For these reasons, the presentation is about the state of the art techniques to track the maximum available output power of photovoltaic systems called maximum power point tracking (MPPT) control systems. This topic could be also one of the most challenges in photovoltaic systems application that has been receiving much more attention worldwide. The talks will cover the application of intelligent techniques by means the artificial neural network (ANN) and fuzzy logic controller scheme using polar information to develop a novel real-time simulation technique for MPPT control by using dSPACE real-time interface system. In this case, the three-layer feed-forward ANN is trained once for different scenarios to determine the global MPP voltage and power and the fuzzy logic with polar information controller takes the global maximum power point (MPP) voltage as a reference voltage to generate the required control signal for the power converter. This type of fuzzy logic rules is implemented for the first time in MPPT control application. The proposed method has been tested using different solar cell technologies such as monocrystalline silicon, thin-film cadmium telluride and triple junction amorphous silicon solar cells. The verification of availability and stability of the proposed system through the real-time simulator shows that the proposed system can respond accurately for different scenarios and different solar cell technologies. In other cases, one of the main causes of reducing energy yield of photovoltaic systems is the partially shaded condition. Although the conventional MPPT control algorithms operate well in a uniform solar irradiance, they do not operate well in non-uniform solar irradiance conditions. The non-uniform conditions cause multiple local maximum power points on the power-voltage curve. The conventional MPPT methods cannot distinguish between the global and local peaks. Since the global power point may change within a large voltage window and also its position depends on shading patterns, it is very difficult to recognize the global operating point under partially shaded conditions. From these reasons, the presentation will address the effectiveness of the proposed MPPT method to solve the partially shaded conditions under the experimental real-time simulation technique based dSPACE real-time interface system for different size of PV arrays, such as 3x3(0.5kW) and 20x3(3.3kW) and different interconnected PV arrays, for instance series-parallel (SP), bridge link (BL) and total cross tied (TCT) configurations.

Effect of oxide based graded buffer and bottom n-layer on the performance of the single junction amorphous silicon solar cells

We have developed oxide based window layer, graded buffer layer and n-layer by radio frequency plasma enhanced chemical vapour deposition (rf-PECVD) method for use in the fabrication of single junction amorphous silicon (a-Si) small area (1 cm2) solar cell. From our earlier study we had observed that higher stabilized efficiency can be obtained using oxide based window and buffer layer. In this study, we have replaced conventional buffer layer by graded buffer (graded with four different band gaps) and conventional n-a-Si:H by wide band gap n-a-SiO:H to improve p/i interface and current density further of a single junction solar cell. The use of these two materials in a single junction a-Si structure enhances the open circuit voltage (Voc) and short circuit current of the cell and the conversion efficiency as well. Graded buffer layer can minimize the p/i interface defects to a large extent causing an improvement of Voc. The bandgap of n-a-SiO:H film is much higher and optical absorption is less than that of n-a-Si:H film having the dark conductivity almost same. Due to low absorption and wide optical gap of n-oxide layer allows more fraction of light enter into the absorber layer after reflection from back reflector resulting in increase in short circuit current. 9.53% of initial efficiency is achieved by the use of graded buffer layer and wide band gap n-layer in single junction small area (1 cm2) solar cell.

Amorphous silicon solar cells on nano‐imprinted commodity paper without sacrificing efficiency

Paper is a cheap substrate which is in principle compatible with the process temperature applied in the plasma enhanced chemical vapour deposition (PECVD) and hot wire CVD (HWCVD) of thin film silicon solar cells. The main drawback of paper for this application is the porosity due to its fibre like structure. The feature size (micrometre scale) is larger than the thickness of the applied photovoltaic layers. To overcome this problem, UV curable lacquer was used to planarize the surface. Plain 80 grams printer paper was taken as a substrate and the lacquer smoothens the rough surface of the paper such that a designed nanostructure can be imprinted for light scattering. In this manner single junction amorphous silicon solar cells with a HWCVD deposited intrinsic layer were processed on paper, without any concessions to the process temperature of 200 °C. The cell performance is comparable to that of reference cells grown on stainless steel, proving that solar cells can be deposited on paper substrates without sacrificing performance. PV on paper could be applied as ”disposable” power source for gadgets, electronic labelling, remote sensing systems, etc. (Internet of Things). (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)

Effect of thermal annealing on the optical and electrical properties of boron doped a-SiOx:H for thin-film silicon solar cell applications

The p-type layer in a p-i-n thin-film solar cell plays a crucial role in determining efficiency. The requirements for p-type layer films are high optical band gap (Eg), narrow valence band tail to minimize optical absorption, high dark conductivity, and low activation energy to reduce the parasitic series resistance of the solar cell. We investigated the effects of temperature during film growth and post-deposition thermal annealing on the optical and electronic properties of p-type amorphous silicon oxide films (p-a-SiOx:H) for thin-film silicon solar cell applications. The activation energy of thermally annealed p-a-SiOx:H film prepared at low substrate temperature decreased from 0.72eV to 0.56eV with similar Eg. Our improvements are explained in the changed ratio of conjugation with the three- and four-fold coordinated boron atoms by the shift of the B (1s) X-ray photoelectron spectrum. Taking into account the reversible electrical change by thermal annealing while maintaining high optical properties, we propose necessary process-procedure conditions for obtaining high photovoltaic performance in thin-film-Si solar cells with high-quality p-a-SiOx:H. We carried out device modeling of p-i-n junction amorphous silicon solar cells by employing a thermal annealing effect on p-type a-SiOx:H layer, using an advanced semiconductor analysis simulator. Due to reduced Ea with high Eg of p-type a-SiOx:H layer after thermal annealing, the solar cell performance of the open circuit voltage, fill factor, and conversion efficiency improved by 11.1%, 60.42%, and 53.75%, respectively.

Fabrication of single junction amorphous silicon solar cell/mini module using novel n-type nanocrystalline SiOx:F:H back reflector

A novel n-type nanocrystalline hydrogenated and fluorinated silicon oxide (nc-SiOx:F:H) based back reflector layer (BRL) has been successfully developed for the fabrication of amorphous silicon based single junction solar cells by radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) technique. Optoelectronic properties, particularly the refractive index (n) suitable for BRL were controlled by varying the oxygen content within the film without compromising the essential nanocrystalline growth. Surface morphology, structural and optical analysis of nc-SiOx:F:H were investigated by using AFM, HRTEM, Raman, FTIR and Ellipsometer. Advantage of this nanocrystalline material as BRL has been demonstrated by incorporating it into a single junction amorphous silicon solar cell and compared its performance with conventional aluminium doped zinc oxide (ZnO:Al) and n doped hydrogenated microcrystalline silicon oxide (n-µc-SiOx:H) based BRL. Single junction thin film a-Si solar cells with initial efficiency ~9.66 % have been successfully fabricated. It is found that the solar cell fabricated using newly developed BRL shows ~6 % more efficiency compared to n-µc-SiOx:H based BRL. Spectral response studies revealed that the improvement was mainly due to enhanced response at visible as well as higher wavelength region.

Development of n-μc-SiOx:H as cost effective back reflector and its application to thin film amorphous silicon solar cells

Development of doped silicon oxide based microcrystalline material as a potential candidate for cost-effective and reliable back reflector layer (BRL) for single junction solar cells is discussed in this article. Phosphorus doped μc-SiOx:H layers with a refractive index ∼2 and with suitable electrical properties were fabricated by radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) technique, using the conventional capacitively coupled reactors. Optoelectronic properties of these layers were controlled by varying the oxygen content within the film. The performance of these layers as BRL have been investigated by incorporating them in a single junction amorphous silicon solar cell and compared with the conventional ZnO:Al based reflector layer. Single junction thin film a-Si solar cells with efficiency ∼9.12% have been successfully demonstrated by using doped SiO:H based material as a back reflector. It is found that the oxide based back reflector shows analogous performance to that of conventional ZnO:Al BRL layer. The main advantage with this technology is that, it can avoid the ex-situ deposition of ZnO:Al, by using doped μc-SiO:H based material grown in the same reactor and with the same process gases as used for thin-film silicon solar cells.

Silica nanoparticles on front glass for efficiency enhancement in superstrate-type amorphous silicon solar cells

Antireflective coating on front glass of superstrate-type single junction amorphous silicon solar cells (SCs) has been applied using highly monodispersed and stable silica nanoparticles (NPs). The silica NPs having 300 nm diameter were synthesized by Stober technique where the size of the NPs was controlled by varying the alcohol medium. The synthesized silica NPs were analysed by dynamic light scattering technique and Fourier transform infrared spectroscopy. The NPs were spin coated on glass side of fluorinated tin oxide (SnO2: F) coated glass superstrate and optimization of the concentration of the colloidal solution, spin speed and number of coated layers was done to achieve minimum reflection characteristics. An estimation of the distribution of the NPs for different optimization parameters has been done using field-emission scanning electron microscopy. Subsequently, the transparent conducting oxide coated glass with the layer having the minimum reflectance is used for fabrication of amorphous silicon SC. Electrical analysis of the fabricated cell indicates an improvement of 6.5% in short-circuit current density from a reference of 12.40 mA cm−2 while the open circuit voltage and the fill factor remains unaltered. A realistic optical model has also been proposed to gain an insight into the system.

Radial junction amorphous silicon solar cells on PECVD-grown silicon nanowires

Constructing radial junction hydrogenated amorphous silicon (a-Si:H) solar cells on top of silicon nanowires (SiNWs) represents a promising approach towards high performance and cost-effective thin film photovoltaics. We here develop an all-in situ strategy to grow SiNWs, via a vapour–liquid–solid (VLS) mechanism on top of ZnO-coated glass substrate, in a plasma-enhanced chemical vapour deposition (PECVD) reactor. Controlling the distribution of indium catalyst drops allows us to tailor the as-grown SiNW arrays into suitable size and density, which in turn results in both a sufficient light trapping effect and a suitable arrangement allowing for conformal coverage of SiNWs by subsequent a-Si:H layers. We then demonstrate the fabrication of radial junction solar cells and carry on a parametric study designed to shed light on the absorption and quantum efficiency response, as functions of the intrinsic a-Si:H layer thickness and the density of SiNWs. These results lay a solid foundation for future structural optimization and performance ramp-up of the radial junction thin film a-Si:H photovoltaics.

A novel structured plastic substrate for light confinement in thin film silicon solar cells by a geometric optical effect

We present a novel method to achieve light trapping in thin film silicon solar cells. Unlike the commonly used surface textures, such as Asahi U-type TCO, that rely on light scattering phenomena, we employ embossed periodically arranged micro-pyramidal structures with feature sizes much larger than the wavelength of visible light. Angular resolved transmission of light through these substrates indeed showed diffraction patterns, unlike in the case of Asahi U-type substrates, which show angular resolved scattering. Single junction amorphous silicon (a-Si) solar cells made at 125°C on the embossed structured polycarbonate (PC) substrates showed an increase in current density by 24% compared to a similar solar cell on a flat substrate. The band gap and thickness of the i-layer made by VHF PECVD are 1.9eV and 270nm respectively. A double p-layer (nc-Si:H/a-Si:H) was used to make proper contact with ZnO:Al TCO.Numerical modeling, called DokterDEP was performed to fit the dark and light current–voltage parameters and understand the characteristics of the cell. The output parameters from the modeling suggest that the cells have excellent built-in potential (Vbi). However, a rather high recombination voltage, Vμ, affects the FF and short circuit current density (Jsc) for the cells on Asahi as well as for the cells on PC. A rather high parallel resistance≫1MΩcm2 (obtained from the modeling) infers that there is no significant shunt leakage, which is often observed for solar cells made at low temperatures on rough substrates. An efficiency of more than 6% for a cell on PC shows enormous potential of this type of light trapping structures.

Optimization of indium tin oxide by pulsed DC power on single junction amorphous silicon solar cells

We investigated the optimal deposition conditions of a thin indium tin oxide (ITO) film on an amorphous silicon (a-Si) single-junction solar cell using pulsed DC magnetron sputtering. Thin ITO films were deposited while power, deposition time, pressure, gas flow and temperature were varied to find such conditions. The efficiency of a-Si solar cells with ITO films was 6.65% at the optimal conditions — a pulsed DC power of 40 W, a deposition time of 460 s, a pressure of 0.53 Pa, gas flow of 16 sccm and 151 °C. On the other hand, an a-SiGe tandem solar cell with the ITO films made at the optimal conditions yields an efficiency of 7.20%. We have also examined the surface morphology of ITO coated a-Si solar cells, using atomic force microscopy. Interestingly, a change in power does not alter the surface morphology at small length scales, whereas at large scales, the lower power sample had a lower surface roughness than the samples made with higher powers. We also find that for the range of deposition conditions examined, the value of the roughness exponent does not change with α ≃ 2/3 and a thin layer of ITO does not modify the surface morphology significantly.

Efficient Anode and Cathode Materials for Amorphous Silicon Solar Cell Driven all Solar Electrolysis of Water

AbstractFew non-noble metal based anode and cathode materials were investigated for all solar electrolysis of water to hydrogen and oxygen gases powered by double junction amorphous silicon (Dj-a-Si) solar cell under solar simulated light of 1 sun. The highest hydrogen generation current efficiency of 58.68% was obtained when Pt wire was used as a cathode with the non-noble metal based Ni-Co

High quality hydrogenated amorphous silicon oxide film and its application in thin film silicon solar cells

Wide gap, high quality hydrogenated intrinsic amorphous silicon oxide (i-a-SiO:H) films have been prepared by very high frequency plasma-enhanced chemical vapor deposition (60 MHz VHF-PECVD) technique for using as an absorber layer for the single junction amorphous silicon solar cells. In this study, we mainly investigated the effect of plasma power density on the defect density of the films, since the defect density is a critical parameter for estimating the thin film silicon-based quality It was found that the defect density was increased with increasing plasma power density. The thin film i-a-SiO:H based solar cells with the structure of TCO/p/i-a-SiO:H/n/ZnO/Ag were fabricated in order to investigate the effects of plasma power density for the i-a-SiO:H deposition on the solar cell performance. The experimental results showed that the conversion efficiency ( η) was improved from 6.8 to 7.3% due to the improvement in fill factor (FF) by decreasing plasma power density from 50.0 to 33.3 mW/cm 2. In comparison with the cell using conventional i-a-Si:H absorber, a peak of the spectra response in the short wavelength region (400–600 nm) was shifted from 600 to 550 nm. These results showed the potential of the i-a-SiO:H films for applying in top cell of multi-junction solar cell in order to improve the light absorption in the short wavelength region.

In Search of Efficient Anode and Cathode Materials for Double Junction Amorphous Silicon Solar Cell Driven all Solar Electrolysis of Water to Hydrogen and Oxygen Gases

Few non-noble metal based anode and cathode materials were investigated for all solar electrolysis of water to hydrogen and oxygen gases powered by double junction amorphous silicon (Dj-a-Si) solar cell under solar simulated light of 1 sun. The highest hydrogen generation current efficiency of 58.68 % was obtained when Pt wire was used as a cathode with the non-noble metal based Ni-Co3O4 as an anode in the electrochemical cell. However, when Pt metal was replaced by a non-noble metal Ni the maximum hydrogen generation current efficiency of 51.28 % was observed. Comparable hydrogen generation current efficiencies were found when Ni-Co3O4 anode or thin RuO2 coated Ti metal anode (RuO2-Ti) was used in combination with Pt metal cathode. The percent solar to hydrogen conversion efficiencies (% STH) were found to be 8.66 % and 8.46 % for the Dj-a-Si solar cell driven electrolysis of water in the Ni-Co3O4||Pt and RuO2-Ti||Pt electrochemical cells respectively. For non-noble metal based electrochemical cell, Ni-Co3O4||Ni the % STH efficiency was found to be 7.57 %.