Amorphous Silicon Cells Research Articles

Sustainable Recycling of Selenium-Based Optoelectronic Devices.

Selenium (Se), the world's oldest optoelectronic material, has been widely applied in various optoelectronic devices such as commercial X-ray flat-panel detectors and photovoltaics. However, despite the rare and widely-dispersed nature of Se element, a sustainable recycling of Se and other valuable materials from spent Se-based devices has not been developed so far. Here a sustainable strategy is reported that makes use of the significantly higher vapor pressure of volatile Se compared to other functional layers to recycle all of them from end-of-life Se-based devices through a closed-space evaporation process, utilizing Se photovoltaic devices as a case study. This strategy results in high recycling yields of ≈ 98% for Se and 100% for other functional materials including valuable gold electrodes and glass/FTO/TiO2 substrates. The refabricated photovoltaic devices based on these recycled materials achieve an efficiency of 12.33% under 1000-lux indoor illumination, comparable to devices fabricated using commercially sourced materials and surpassing the current indoor photovoltaic industry standard of amorphous silicon cells.

Comprehensive Analysis of Spectral Mismatch Factor for Solar Cells Based on In Situ Observation of Aerosol Optical Depth Spectra and Solar Spectral Irradiance in Korea

The spectral mismatch factor for solar cells quantifies their relative performance in converting solar irradiance between the incident and reference solar spectra into electricity. This study attempted to evaluate the spectral mismatch factor for eight types of solar cells and investigate their sensitivity to changes in the solar spectral irradiance, which is dependent on the aerosol optical properties in a clear sky. Copper indium gallium diselenide cells have the highest mean value of the spectral mismatch factor, implying that they are less sensitive to changes in the solar spectral irradiance. In contrast, perovskite and amorphous silicon cells are more sensitive to atmospheric conditions, with broader distributions of the spectral mismatch factor values. Additionally, our study found that heterojunction with intrinsic thin-layer cells has the highest substantial efficiency, considering the nameplate efficiency. The spectral mismatch factor decreased with increasing aerosol optical depth at 500 nm and was proportional to the humidity. The effects of aerosol optical properties on the spectral mismatch factor for different solar cells were clarified using clustering analysis and back-trajectory modeling results. In the present study, the aerosol optical depth spectra were found to be more important in determining the spectral mismatch factor than the aerosol optical depth at 500 nm. This study recommends further research on the relationship between the aerosol optical properties and solar spectral irradiance to better predict or estimate the spectral mismatch factor in solar power forecasting.

Indoor photovoltaics awaken the world's first solar cells.

Selenium (Se) solar cells were the world's first solid-state photovoltaics reported in 1883, opening the modern photovoltaics. However, its wide bandgap (~1.9 eV) limits sunlight harvesting. Here, we revisit the world's oldest but long-ignored photovoltaic material with the emergence of indoor photovoltaics (IPVs); the absorption spectrum of Se perfectly matches the emission spectra of commonly used indoor light sources in the 400 to 700 nm range. We find that the widely used Te adhesion layer also passivates defects at the nonbonded Se/TiO2 interface. By optimizing the Te coverage from 6.9 to 70.4%, the resulting Se cells exhibit an efficiency of 15.1% under 1000 lux indoor illumination and show no efficiency loss after 1000 hours of continuous indoor illumination without encapsulation, outperforming the present IPV industry standard of amorphous silicon cells in both efficiency and stability. We further fabricate Se modules (6.75 cm2) that produce 232.6 μW output power under indoor illumination, powering a radio-frequency identification-based localization tag.

Modelling of Novel Architecture of PV Generator Based on a-Si: H/c-Si Materials and Using Solar Tracker for Partial Shading

The purpose of this study is to investigate the shading effect on a novel architecture of photovoltaic generator (PVG) proposed in this paper. This architecture consists of three photovoltaic (PV) modules in series connected. Two of them consist of amorphous silicon cells in series connected. The third module consists of monocrystalline silicon cells in series connected. This architecture is conceived as a PV concentrator, where the two amorphous PV modules are located in the lower position, and the third one is located in the upper position precisely in the focus. The role of the upper module is to absorb the solar rays, which are reflected by the two other modules to gain the maximum of solar energy. This novel architecture is aimed at solving the problems existing with the architecture of tandem solar cells proposed in literature. Those problems are the mismatch between cells and the tunnel junction costs and fabrication. In this work, we use MATLAB/Simulink for modelling this architecture and studying its characteristics (I–V and P–V) in case of partial shading. Through this study, it was found that the maximum PV power is affected by the partial shading. To solve this problem, we have implemented in this work a solar tracker.

Washable textile embedded solar cells for self-powered wearables

PurposeSolar cells could make textile-based wearable systems energy independent without the need for battery replacement or recharging; however, their laundry resistance, which is prerequisite for the product acceptance of e-textiles, has been rarely examined. This paper aims to report a systematic study of the laundry durability of solar cells embedded in textiles.Design/methodology/approachThis research included small commercial monocrystalline silicon solar cells which were encapsulated with functional synthetic textile materials using an industrially relevant textile lamination process and found them to reliably endure laundry washing (ISO 6330:2012). The energy harvesting capability of eight textile laminated solar cells was measured after 10–50 cycles of laundry at 40 °C and compared with light transmittance spectroscopy and visual inspection.FindingsFive of the eight textile solar cell samples fully maintained their efficiency over the 50 laundry cycles, whereas the other three showed a 20%–27% decrease. The cells did not cause any visual damage to the fabric. The result indicates that the textile encapsulated solar cell module provides sufficient protection for the solar cells against water, washing agents and mechanical stress to endure repetitive domestic laundry.Research limitations/implicationsThis study used rigid monocrystalline silicon solar cells. Flexible amorphous silicon cells were excluded because of low durability in preliminary tests. Other types of solar cells were not tested.Originality/valueA review of literature reveals the tendency of researchers to avoid standardized textile washing resistance testing. This study removes the most critical obstacle of textile integrated solar energy harvesting, the washing resistance.

A high gain solar cell aperture‐coupled patch antenna based on substrate‐integrated suspended line platform for 5G application

AbstractThe aperture‐coupled patch antenna integrated with the amorphous silicon solar cell based on the substrate‐integrated suspended line platform is presented in this letter. The antenna patch on G1 layer is used as the cathode of amorphous silicon cell and the 1 × 2 array antenna is proposed based on the unit. The solar cell antenna operating from 4.67 to 5.17 GHz has the characteristic of high gain, which is achieved by air coupling to reduce loss. The gain of the unit and array is 9.21 and 11.92 dBi, respectively. In addition, the results of the antennas with and without solar cells are little different.

Parametric Analysis of a Novel Photovoltaic/Thermal System Using Amorphous Silicon Cells and Micro-Channel Loop Heat Pipes

Photovoltaic/thermal (PV/T) systems are taking up an increasing market share owing to a high overall solar energy efficiency. An innovative PV/T system that combines amorphous silicon cells and micro-channel loop heat pipes is proposed in this paper. It can overcome problems of large thermal stress at fluctuating temperature and frosting in winter which exist in conventional PV/Ts using crystalline silicon cells and copper tube heat exchangers. A distributed parameter model is built and experimental validation on heat transfer and electricity generation is conducted. The parametric influences of thickness of air interlayer, cover factor, number of MCHPs, area of condenser are investigated. The results indicate that the overall energy efficiency increases from 22.30% to 47.61% as the thickness of air interlayer rises from 0 to 15 mm. A number of MCHPs of 8–14 and length of condenser of 4–6 m are recommended for the sake of cost-effectiveness, and the corresponding thermal and electrical efficiencies are about 47% and 6%. The proposed PV/T system can efficiently harness solar heat with a minor impact on electricity output and has significant potential in the medium temperature applications.

Spectral mismatch and its effect on artificial solar light source under standard test conditions

Under standard test conditions, the spectral irradiance of artificial solar light sources and the spectral response of photovoltaic devices are important factors that affect the accuracy of device test results. This paper takes the standard solar spectrum AM1.5 as a reference, and calculates the difference between the four commonly used artificial solar light sources (Arc Lamp, Q-Flash, Q-Flash w and ELH) and the standard solar spectrum AM1.5 from the perspective of spectral mismatch. The spectral mismatch factor and the output parameters of the amorphous silicon cell under the irradiation of these light sources. Calculations show that the spectral mismatch factor of Arc Lamp is only 1.005, which matches the standard solar spectrum AM1.5 best. Due to the effect of spectral mismatch, the output parameters of amorphous silicon cells will change significantly after different artificial light sources irradiate them.

Comparative study on energy and exergy properties of solar photovoltaic/thermal air collector based on amorphous silicon cells

This paper compared the performance of solar photovoltaic/thermal (PV/T) air collectors (SPVTAC) based on amorphous silicon solar cells with traditional solar air collectors and individual photovoltaic (PV) modules. The SPVTAC was proposed to overcome the problems of large thermal stresses at fluctuating temperatures and frost in winter, and also due to their working suitability in medium–high temperature ranges. The energy and exergy performance of the three devices were tested and analyzed with different airflow rates, inlet temperatures and solar irradiance. The experimental results show that the thermal efficiency of SPVTAC was approximately 25% lower than the traditional solar air collector at the same operating condition. Also, the electrical efficiency of SPVTAC was higher than the individual PV system (4.65%) when the air mass flow rate was over 0.040 kg/s. For each degree increase in the inlet temperature, the thermal efficiency of the amorphous silicon SPVTAC decreased by approximately 0.45%, the electrical efficiency decreased by approximately 0.042% and the temperature difference between the inlet and outlet decreased by 0.24 °C. The maximum total exergy efficiency of the SPVTAC (12.22%) and the maximum thermal exergy efficiency of the traditional solar air collector (8.71%) was achieved at an inlet air temperature of 60 °C. These experimental results provide a reference for further applications of amorphous silicon solar cells integrated with SPVTAC.

Promising Shadow Masking Technique for the Deposition of High-Efficiency Amorphous Silicon Solar Cells Using Plasma-Enhanced Chemical Vapor Deposition

In this work, a detailed description of the various steps involved in the fabrication of high-efficiency hydrogenated amorphous-silicon cells using plasma-enhanced chemical vapor deposition, and a novel shadow masking technique is presented. The influence of the different masking methods on the cell parameters was experimentally investigated. Particularly, the short-circuit current density (Jsc), the fill factor, the open circuit voltage (Voc), and the resistive losses indicated by the shunt (Rsh) and series (Rs) resistances were measured in order to assess the performance of the cells as a function of the masks used during the cell fabrication process. The results indicate that the use of a masking technique where the p-i-n structure was first deposited over the whole surface of a 20 cm2 × 20 cm2 substrate, followed by the deposition, deposits the back contact through a metal mask, and by the ultrasonic soldering of indium to access the front contact is a good alternative to laser scribing in the laboratory scale. Indeed, a record efficiency of 8.8%, with a short-circuit current density (Jsc) of 15.6 mA/cm2, an open-circuit voltage (Voc) of 0.8 V, and a fill factor of 66.07% and low resistive losses were obtained by this technique. Furthermore, a spectroscopic ellipsometry investigation of the uniformity of the film properties (thickness, band gap, and refractive index) on large-area substrates, which is crucial to mini-module fabrication on a single substrate and for heterojunction development, was performed using the optimal cell deposition recipes. It was found that the relative variations of the band gap, thickness, and refractive index n are less than 1% suggesting that the samples are uniform over the 20 cm2 × 20 cm2 substrate area used in this work.

Investigation of an innovative PV/T-ORC system using amorphous silicon cells and evacuated flat plate solar collectors

Solar-driven organic Rankine cycle (s-ORC) power generation is a promising technology with thermal storage for flexible operation to meet domestic variable electricity demand. A satisfactory efficiency of this technology can be obtained only at medium-to-high temperature, for which conventional flat plate and evacuated tube solar collectors are not suitable while solar concentrators cannot efficiently utilize diffuse solar radiation. Evacuated flat plate (EFP) collectors have recently been developed for efficient solar heat collection in the temperature range from 100 to 200°C, suitable for the ORC system. At present, the cost of EFP collectors is relatively high and will lead to a long payback period of the s-ORC system. To increase the annual power yield and reduce the payback time, inexpensive amorphous silicon (a-Si) solar cells are proposed to be integrated into the EFP collectors. It is the first time to put forward such photovoltaics/thermal (PV/T) design combining a-Si cells and EFP collectors. Compared with polycrystalline silicon cells (poly-Si), a-Si cells may have a higher electrical efficiency at a higher operating temperature due to the thermal annealing effect and are expected to have a long lifetime without encapsulation in the vacuum environment provided by the EFP collectors. In this study, the a-Si PV/T-ORC system using EFP collectors is investigated. Transient performance analysis of a-Si PV/T-ORC is given for the weather data of two selected days. A comparison is also made with a stand-alone poly-Si PV system, poly-Si PV/T-ORC system and s-ORC system with EFP collectors alone, respectively. The results indicate that for a typical day in July, the a-Si PV/T-ORC system has the highest daily power output of 0.822 kWh/m2, 102.3% more than the s-ORC system, 23.8% more than the stand-alone poly-Si PV system and 12% more than the poly-Si PV/T-ORC system, respectively.

Ag@SiO<sub>2</sub> coupled structure’s design and regulation and control of response to thin film solar cells

The coupled nano-structure Ag@SiO<sub>2</sub> has both plasmon excitation like metallic nanoparticles and diffraction scattering like a dielectric nanosphere, which effectively controls the propagation path and the energy distribution of incident light and shows great potential applications in light trapping for thin film solar cells. In this work, we construct a three-dimensional electromagnetic model based on the finite-difference time-domain (FDTD) and rigorous coupled-wave analysis (RCWA) method to investigate the regulation mechanism of Ag@SiO<sub>2</sub> coupling structure to the spectral response of amorphous silicon cells. By being optimally designed, a high-efficiency cell device is achieved. The results show that the transmitted light into the active layer reaches a maximum value when Ag and SiO<sub>2</sub> have their feature sizes of 18 and 150 nm, respectively. The absorption spectrum of the corresponding cell device also arrives at its maximum value. The photoelectric conversion efficiency is enhanced from 7.19% to 7.80%, with an increment of 8.48% compared with the flat solar cell with an equivalent thickness of absorbing layer.

Feasibility of an innovative amorphous silicon photovoltaic/thermal system for medium temperature applications

Medium temperature photovoltaic/thermal (PV/T) systems have immense potential in the applications of absorption cooling, thermoelectric generation, and organic Rankine cycle power generation, etc. Amorphous silicon (a-Si) cells are promising in such applications regarding the low temperature coefficient, thermal annealing effect, thin film and avoidance of large thermal stress and breakdown at fluctuating temperatures. However, experimental study on the a-Si PV/T system is rarely reported. So far the feasibility of medium temperature PV/T systems using a-Si cells has not been demonstrated. In this study, the design and construction of an innovative a-Si PV/T system of stainless steel substrate are presented. Long-term outdoor performance of the system operating at medium temperature has been monitored in the past 15 months. The average electrical efficiency was 5.65%, 5.41% and 5.30% at the initial, intermediate and final phases of the long-test test, accompanied with a daily average thermal efficiency from about 21% to 31% in the non-heating season. The thermal and electrical performance of the system at 60 °C, 70 °C and 80 °C are also analyzed and compared. Moreover, a distributed parameter model with experimental validation is developed for an inside view of the heat transfer and power generation and to predict the system performance in various conditions. Technically, medium temperature operation has not resulted in interruption or observable deformation of the a-Si PV/T system during the period. The technical and thermodynamic feasibility of the a-Si PV/T system at medium operating temperature is demonstrated by the experimental and simulation results.

Continuous performance assessment of thin-film flexible photovoltaic cells under mechanical loading for building integration

Building integration using thin-film flexible photovoltaic (PV) cells with load-carrying structures requires understanding of their electrical performance under continuous mechanical loadings. Limited results mainly focus on the electrical performance of PV cells under certain fixed mechanical strains. In this paper, an approach is examined to continuously apply tensile strains on PV cell specimens; therefore the short circuit current (ISC) and open circuit voltage (VOC) are constantly monitored. Two types of PV cells are studied under the proposed approach including amorphous silicon (a-Si) and organic PV cells and the results demonstrate its practicability to determine the critical tensile strains reliably for both PV types. It is found that VOC is more sensitive than ISC to the applied tensile strain for both types of PV cells and substantial degradation in VOC for a-Si cells initiates at the tensile strain of 1.51%. For organic cells, significant reduction in VOC is observed at the critical tensile strain of 1.46% in association with yielding of the substrate. While noticeable degradation can be only observed in ISC from 1.67% strain for a-Si PV cells and from 3.09% strain for organic ones. In addition, linear declines with temperature in VOC of both PV types are quantified for temperatures over 30 °C.

Experimental study on a novel photovoltaic thermal system using amorphous silicon cells deposited on stainless steel

Amorphous silicon (a-Si) cells are able to perform better as temperature increases due to the effect of thermal annealing. a-Si cells have great potential to solve or ease the problems of high power temperature coefficient, large thermal stress caused by temperature fluctuation and gradient, and thick layer of conventional crystalline silicon cell-related photovoltaic/thermal (PV/T) collectors. In this paper, an innovative a-Si PV/T system is developed. It is the first time that a-Si cells deposited on stainless steel have been used in a practical PV/T system. The system comprises of two PV/T collectors. In each collector, there are 8 pieces of solar cells in series. Long-term outdoor performance has been monitored. Experimental results on the thermal efficiency (ηth), electrical efficiency (ηPV) and I-V characteristic are presented. The peak instantaneous ηth,p was about 42.49% with the maximum ηPV,p of 5.92% on April 2, 2017. The daily average ηth,a and ηPV,a were 32.8% and 5.58%. Accordingly, ηth,p, ηPV,p, ηth,a and ηPV,a on October 27 were 43.47%, 5.69%, 38.65% and 5.22%. During more than half a year operation, no technical failure of the system has been observed. The feasibility of the a-Si PV/T is preliminarily demonstrated by the prototype.

Luminescent layers based on rare earth elements for thin-film flexible solar cells applications

Flexible inorganic solar cells are nowadays produced commercially on polymer and metal foils. Many technological enhancements are used to increase their conversion efficiency. In this paper authors focused on down conversion of ultraviolet and short wavelength visible light for improvement of amorphous silicon cells’ quantum efficiency. Towards this goal, rare-earth elements were applied as active particles in flexible polymer down converting layer. For practical experiments, screen-printing method, as the cheap, reliable and industrially-ready technology was used. Various materials composition as well as different layer thicknesses and morphology were tested in order to obtain optimal luminescent effect.

Efficiency of polycrystalline photovoltaic parks in Romania: Possibility of using renewable energy

The performance of photovoltaic panels and lifetime are determined to a large extent by the quality of photovoltaic cells, their soldering technology, the quality of ethyl vinyl acetate film in which they are encapsulated, the encapsulation technology and the back sheet. Depending on the manufacturing technology, photovoltaic panels can be made of monocrystalline, polycrystalline, and amorphous silicon cells. This manuscript studies the main factors that influence the aging of photovoltaic panels in order to assess their effectiveness and sustainability in terms of energy, in order to establish the optimum conditions of photovoltaic panel?s location, being a contribution to the attainment of the targets in terms of growth using renewable sources of energy. The main purpose of this research is to study the current state, in Romania, in the field of renewable energies by using solar panels.

Comparing energy performance of different semi-transparent, building-integrated photovoltaic cells applied to “reference” buildings

Semi-transparent, building-integrated photovoltaics (BIPVs) are receiving significant attention by several research groups, given their increasing efficiencies combined to improved visual performance (being cell transparency and color rendering index, two key features to ensure their widespread use). Several technologies have been developed in the last years, based on the use of amorphous silicon cells, Cu(In,Ga)Se2 (CIGS) cells, organic PV cells, photoelectrochemical (DSC) cells, and perovskite-based cells. Each technology has pros and cons, but among them the two most reliable and promising seem to be the first one (ηSTC= 3-6% and Tvis= 7-40%) and the last one (ηSTC= 6.6% and Tvis= 42.4%). The second, in particular, may be processed so to appear neutrally colored, resulting in a substantially gray glass, while the first one, absorbing nearly all the blue-green radiation, presents an orange-brown coloration. The paper investigates how the use of both technologies affects the energy balance of buildings. For this purpose the EnergyPlus platform was employed and two validated reference buildings were used for comparison (one residential and one office building). Energy yield due to BIPV technologies, variation in heating and cooling loads due to cell transparency, and implications on visual comfort and on artificial lighting usage are finally discussed.

Effect of New Ellipse Design on the Performance Enhancement of PV/T Collector: CDF Approach

Photovoltaic and thermal collectors are combined via a photo­voltaic/thermal (PV/T) collector system to increase collector efficiency. The efficiency of photovoltaic collectors is known to decrease when ambient temperature increases and vice versa. PV/T collector systems function by absorbing the heat gained from the sun via photovoltaic panels and by converting this heat into electrical energy. Simulations CFD have been investigated to explore the impact of different mass flow rates against photovoltaic and thermal efficiencies of PVT collector using FVM. New ellipse design of collectors have been modeled and investigated to generate hot water and electricity. In this simulation, the absorber collectors were assumed to be attached underneath the photovoltaic (PV) module, and water is used as a heat transfer medium in absorber collectors. The results shown that new ellipse absorber collector generates a combined PV/T efficiency of 74.3% with electrical efficiency of 13.78%. The efficiency of the PV/T system should be improved further by developed the surfaces between the absorber and solar panel (PV module). However, different types of PV cells, such as amorphous silicon cells with black mat surface properties, should be used to improve the thermal absorption of PV/T systems. Highlights: (i) A three-dimension hybrid photovoltaic/thermal solar collector module was performed in CFD software; (ii) The results agree with those obtained through steady-state characterization; (iii) The simultaneous use of new ellipse design of absorber, which absorbs much more thermal energy compared to other normal designs, increase thermal and electrical efficiency significantly.

Amorphous Silicon Solar Vivaldi Antenna

An ultrawideband solar Vivaldi antenna is proposed. Cut from amorphous silicon cells, it maintains a peak power at 4.25 V, which overcomes a need for lossy power management components. The wireless communications device can yield solar energy or function as a rectenna for dual-source energy harvesting. The solar Vivaldi performs with 0.5-2.8 dBi gain from 0.95-2.45 GHz , and in rectenna mode, it covers three bands for wireless energy scavenging.