The Simultaneous Impacts of the p nc-SiOx:H Window Layer Band Gap and the Back Reflection on the Performances of a-Si:H Based Solar Cells (original) (raw)
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AIP Advances, 2015
Thin film solar cells are cheaper but having low absorption in longer wavelength and hence, an effective light trapping mechanism is essential. In this work, we proposed an ultrathin crystalline silicon solar cell which showed extraordinary performance due to enhanced light absorption in visible and infrared part of solar spectrum. Various designing parameters such as number of distributed Bragg reflector (DBR) pairs, anti-reflection layer thickness, grating thickness, active layer thickness, grating duty cycle and period were optimized for the optimal performance of solar cell. An ultrathin silicon solar cell with 40 nm active layer could produce an enhancement in cell efficiency ∼ 15 % and current density ∼ 23 mA/cm 2. This design approach would be useful for the realization of new generation of solar cells with reduced active layer thickness.
Effect of back reflectors on photon absorption in thin-film amorphous silicon solar cells
Applied Nanoscience, 2017
In thin-film solar cells, the photocurrent conversion productivity can be distinctly boosted-up utilizing a proper back reflector. Herein, the impact of different smooth and textured back reflectors was explored and effectuated to study the optical phenomena with interface engineering strategies and characteristics of transparent contacts. A unique type of wet-chemically textured glass-substrate 3D etching mask used in superstrate (p–i–n) amorphous silicon-based solar cell along with legitimated back reflector permits joining the standard light-trapping methodologies, which are utilized to upgrade the energy conversion efficiency (ECE). To investigate the optical and electrical properties of solar cell structure, the optical simulations in three-dimensional measurements (3D) were performed utilizing finite-difference time-domain (FDTD) technique. This design methodology allows to determine the power losses, quantum efficiencies, and short-circuit current densities of various layers in such solar cell. The short-circuit current densities for different reflectors were varied from 11.50 to 13.27 and 13.81 to 16.36 mA/cm2 for the smooth and pyramidal textured solar cells, individually. Contrasted with the comparable flat reference cell, the short-circuit current density of textured solar cell was increased by around 24%, and most extreme outer quantum efficiencies rose from 79 to 86.5%. The photon absorption was fundamentally improved in the spectral region from 600 to 800 nm with no decrease of photocurrent shorter than 600-nm wavelength. Therefore, these optimized designs will help to build the effective plans next-generation amorphous silicon-based solar cells.
Dhaka University Journal of Science
In this work, the solar cell design parameters like- layer thickness, bandgap, donor and acceptor concentrations are varied to find optimum structure of a hydrogenated amorphous silicon (a-Si:H) and hydrogenated microcrystalline silicon (μc-Si:H) heterojunction p-i-n solar cell. A thin a-Si:H p-layer of 1 to 5 nm followed by a thick a-Si:H i-layer of thickness 1400 to 1600 nm and then thin n-layer of thickness 1 to 5 nm with acceptor concentration of 102 cm−3 and donor concentration of 1020 cm−3 and the bandgaps of p-, i-, and n- layers with higher bandgaps closer to 2.2 eV for a-Si:H p-layer, 1.85 eV for a-Si:H i-layer, and 1.2 eV for μc-Si:H n-layer have showed better performances. The optimum cell has a JSC of 18.93 mA/cm2, VOC of 1095 mV, Fill factor of 0.7124, and efficiency of 14.77%. The overall external quantum efficiency of the numerically designed cell also remained very high from 85-95 % for wavelengths of 300-650 nm range. This indicates that the device will perform its ...
Thin Solid Films
The relation between the open-circuit voltage (V oc) of hydrogenated amorphous silicon (a-Si:H) solar cells and the band gap of the absorber layer has been investigated by changing the substrate temperature of the absorber layer. By decreasing the substrate temperature from 200°C to 150°C the V oc has increased by 0.05V. However, the temperature dependence of the V oc is larger than the change of the optical band gap of individual intrinsic layers, which indicates that also other absorber layer properties play an important role. Using simulations the effect of changing the mobility gap of as well the absorber layer as the buffer layer at the p-i interface on the performance of a-Si:H solar cells has been investigated. The recombination rate profile in the solar cell at the V oc is a useful tool to analyze and optimize different parts of the solar cell to obtain a high V oc. The simulations confirm the trend of increasing the V oc when implementing absorber layers with a higher mobility gap. The simulations demonstrate that increasing the mobility gap of the buffer layer at the p-i interface results in a further improvement of the V oc , however an optimal value of the mobility gap is found with respect to the conversion efficiency.
The study of spectral variations is very important in the characterization of silicon solar cells. The spectral variations of monocrystalline, polycrystalline and amorphous solar cells is studied through the spectral response with the help of spectral response evaluation meter, CEP-25HS-50SR. PV Syst 6.4.3 software is used to study the variation of air mass throughout the day and the year and to understand that how solar irradiance varies with the changing air mass. As per the findings, the spectral sensitivity of monocrystalline and polycrystalline silicon solar lies in the entire visible region and partial UV and infrared region of solar spectrum whereas amorphous silicon solar cells have a narrow spectral range. This is most likely due to partial absorption of the long wavelength photon. It is observed that with the increase in value of zenith angle and air mass there's a continuous decrease in light intensity received in the form of solar radiation. The intensity of solar radiations decreases because of atmospheric refraction which further decreases the spectral response value and hence the power output power of the silicon solar cells is affected adversely.
Ag/ZnO back reflectors (BR) on specular stainless steel substrates are optimized for hydrogenated amorphous silicon germanium alloy (a-SiGe:H) and nanocrystalline silicon (nc-Si:H) solar cells. The BRs are deposited using a sputtering method. The texture of the Ag and ZnO layers is controlled by deposition parameters as well as chemical etching with diluted HCl. The surface morphology is investigated by atomic force microscopy. The scattered light intensity from a He-Ne laser, which illuminates the sample surface perpendicularly, is measured at different angles. Finally, a-SiGe:H and nc-Si:H solar cells are deposited on the BR substrates prepared under various conditions. For a-SiGe:H bottom cells, the improved BR with large micro-features leads to an enhanced open-circuit voltage. For the nc-Si:H solar cells, large micro-features on the improved BR eliminate interference fringes otherwise observed in the quantum efficiency measurement and result in high short circuit current density. The result is consistent with an enhanced scattered light intensity. Hence, the cell performance was improved. We also deposited a-Si:H/a-SiGe:H/nc-Si:H triple-junction cells on the optimized BR and achieved a high initial active-area efficiency of 14.6%.
Analysis of thin silicon solar cells for high efficiency
Solar Energy Materials and Solar Cells, 1994
A comprehensive theoretical analysis taking into account the contribution from both the emitter and base regions having finite surface recombination velocity has been developed for computing short-circuit current, open-circuit voltage, and efficiency of thin AR coated thin silicon solar cells with textured front surface. The dependence of efficiency on the front surface and back surface recombination velocities and on the cell parameters have been investigated in details for varying cell thickness considering the effects of bandgap narrowing and Auger recombination in the material. It is shown that efficiency exceeding 24% can be attained with silicon solar cells having thickness as low as 25 i~m provided both front and back surfaces are well passivated (S < 103 cm/s) and the doping concentration in the base and emitter are in the range of 5 × 1016 to 1017 cm-3 and 1018 to 5 × 1018 cm-3, respectively. It is also shown that an efficiency of about 23% can be obtained for thin cells of 25 Ixm thickness with a much inferior quality materials having diffusion length of about 40 p.m.
Development of multilayer back reflectors for improved a-Si based solar cell performance
Conference Record of the Thirty-first IEEE Photovoltaic Specialists Conference, 2005.
A new back reflector comprised of an Al/(multi-layered stack)/ZnO structure is being developed to replace AllZnO used in manufacturing and boost conversion efficiencies with improved back reflector performance. Use of the multi-layered stack should lead to improved reflectivity that will in turn improve solar cell currents and efficiencies. Using TCOs with low indices of refraction between 1.6 and 1.7, Af(specular)/MUZnO back reflectors have been fabricated with reflectance values in the red portion of the light spectrum (600-1 000nm) that are close to those obtained with the AI/MgF2/Si/MgF2 optical stacks and AglZnO back reflectors. With the Al(specular)/ML/ZnO back reflector stacks, a 1.7 W c m 2 improvement in the red light short circuit curren! has been obtained for a-SiGe cells. However, the gain in red light efficiency is not as large as expected with textured back reflectors. Improvements should come through re-optimization of the the multi-layer stack or use of different texturing schemes.
Enhance the solar cell efficiency by reduction of reflection losses
IOP Conference Series: Materials Science and Engineering, 2019
The enhancement of the solar cell efficiency field has been achieved in many methods due to the different factors and conditions that led to loss the solar energy. This work deals with the increasing of the efficiency of solar cell that made of single crystalline silicon. This increment achieved by the reduction of biggest type of losses of the conversion efficiency named reflection. by using two methods first; forming grooves on the surface using pulse Nd:YAG laser with max energy 1J and pulse width 10ns, using the fast and accurate movement of the 3D optical galvo mirror scanning system to form the grooves, the second method was by deposition nanomaterials as Silver (Ag) and Cadmium telluride (CdTe) to constitute an antireflection layer for the incident solar spectrum. The effect of antireflection layer material type and the effect of incident light angle on the reflection had been studied in this work. The reflectance had been measured by a system designed and built to give the r...