Ultra-thin Film Solar Cells Research Articles

Computational Study of Moth-Eye Structures for Silicon Solar Cells Lights Harvesting Improvement

Abstract Recently Moth-Eye nanostructure is widely used in solar cell light harvesting enhancement, in this computational work, three different designs; rectangular, triangular, and semi-circular structures were introduced as anti-reflect structures placed above a silicon solar cell, anti-reflected nanostructured modeled and optimized for silicon ultra-thin film solar cells using the finite difference time domain method for optical, and Lumerical devise software for electrical properties study. The effect of the geometrical dimension of the three structures was investigated. It is found that light-harvesting and solar cell performance can be enhanced by choosing a suitable structure and dimension for the suggested structure. The optimum efficiency enhancement achieved was by a semi-circular structure with a radius of 200nm from 8.81% to 11.95%.

Broadband light absorption enhancement in a–Si:H ultrathin film solar cells with nanophotonic light trapping structures

Light trapping over a wide wavelength range is critical for applications such as thin-film solar cells (TFSCs). Therefore, in this paper, we report a plasmonic light trapping scheme as a solution to overcome the limited absorption of light in hydrogenated amorphous silicon (a-Si:H) thin film solar cells. Here we propose plasmonic nanostructures, which have periodic nanodisks added to the front surface of the cell. These structures combine a variety of photonic effects to reduce reflection, improve light trapping, and increase absorption over a broadband solar spectrum. Initially, to test whether the suggested plasmonic nanoparticles can enhance light-trapping within the absorber layers of the cell, we used the 3D finite difference time domain method to simulate the propagation of electromagnetic waves and the absorbed light in each layer of the cell. Additionally, the obtained optical properties after the FDTD simulation are used to design electrical model simulations using SCAPS software. The results show that the front surface of nanodisk-shaped solar cells with only a 100-nm-thick a-Si:H layer can absorb light at wavelengths ranging from 300 to 800 nm, which is greater than that of flat a-Si:H film devices. With optimized structural parameters, the short circuit current density Jsc could be enhanced by 98 % and 71 % with the addition of Au and Cu nanodisks, respectively. Additionally, the conversion efficiency is improved by 28 % and 26 % for Au and Cu, respectively. The proposed design of the light trapping structure can provide guidelines for ultra-TFSCs with high performance.

High performance GaAs ultrathin film solar cell based on optimized antireflection coating and dielectric nano-cylinders

This study presents an ultrathin crystalline GaAs solar cell consists of titanium dioxide (TiO2) nano-cylinders partially embedded in the GaAs film and covered by a proper antireflection coating. For light trapping over the solar spectrum and consequently, enhancing the optical and electrical characteristics of the cell, the thickness and refractive index (RI) of the antireflection coating and the embedding depth of the nano-cylinders in the GaAs film have been optimized. Also, aluminum (Al) metallic layer is applied at the backside of the cell to obtain a higher absorption at longer wavelengths due to photon reflection into the GaAs film. In the suggested solar cell, improvements of 70.65 % and 78.12 % in the short current density (JSC) and the power conversion efficiency are obtained, respectively compared to the conventional GaAs solar cell (Case 1).

Characterization of CdS/CdTe Ultrathin-Film Solar Cells with Different CdS Thin-Film Thicknesses Obtained by RF Sputtering

The development of semitransparent CdS/CdTe ultrathin solar cells has been delayed as a result of the activation annealing to which the device must be subjected, which may involve problems such as the sublimation of ultrathin films and the diffusion of Cd and S at the interface. In this work, CdS/CdTe ultrathin devices on soda-lime glass/SnO2:F/ZnO substrates were obtained by RF magnetron sputtering. CdS/CdTe ultrathin heterostructures were obtained with the following thicknesses for the CdS thin film: 70, 110, and 135 nm. The CdTe thickness film was kept constant at 620 nm. Subsequently, activation annealing with CdCl2 was carried out at 400 °C. Surface characterization was performed by scanning electron microscopy, which indicated that the CdCl2 annealing tripled the CdTe thin films’ grain size. Raman characterization showed that CdS thin films deposited by RF sputtering present the first, the second, and the third longitudinal optical modes, indicating the good crystallinity of the CdS thin films. The study showed that the photovoltaic properties of the CdS/CdTe ultrathin devices improved as the CdS thicknesses decreased.

Enhancement of light absorption by ultra-thin film solar cells using graded gratings

In this study, we developed a novel method based on uniform and graded gratings on the front surface of ultra-thin film Si solar cells to enhance light absorption. The proposed gratings were designed in two configurations comprising penetration into the active layer and placement on it. These structures enhance absorption by scattering and diffracting light, and enlarging the optical path for photons. Simulations based on the finite element method and finite difference time domain technique showed that the graded gratings could significantly enhance absorption in the visible and infrared regions. The maximum current density and efficiency achieved for graded gratings placed on the top surface of the active layer were 21.7 mA/cm2 and 23.9%, respectively (47.6% and 48.4% higher compared with the reference cell).

Absorption enhancement of ultra-thin film Solar Cell using Fabry-Perot and plasmonic modes

In this paper, we investigate the photonic and plasmonic modes in order to enhance the absorption of ultrathin film Si Solar Cells. The simulations based on FEM show that these mechanisms enhance the absorption of the cell significantly. In order to investigate the plasmonic effects and use the amazing optical properties of localized surface plasmons (LSPs), multiple Au nanoparticles (NPs) with different radii have been used on the front surface of the Cell. Simulations show that the use of Au NPs with radii of 25, 50, and 75 nm simultaneously on the front surface of the Cell, increases the absorption dramatically. It is observed that multiple Au NPs with configuration illustrated in Case 5, enhance the absorption significantly due to the excitation of the multiple plasmonic modes in UV and Visible regions. In order to enhance the absorption in near-IR, we use Cu NPs on the backside of the cell. The highest average absorption of 84.7%, short-circuit current density of 36.7 (mA/cm2), and efficiency of 30.1% is achieved, with an increase of 177.7%, 178%, and 178.7% compared to Case 1, respectively. These methods promise the performance improvement of ultra-thin film solar cells and increase their application potential in Solar energy harvesting.

Plasmonic enhanced ultra-thin solar cell: A combined approach using fractal and nano-antenna structure to maximize absorption

In this study, a combined structure is proposed to develop ultra-thin silicon solar cells. This integrated structure consists of silver fractal-like nano-particles and leaky wave nanoantennas. The nano-cuboid pattern embedded inside anti-reflective coating benefits from different optical modes, such as surface plasmons and cavity modes, which trap more light and amplify the electric field in the upper region of the absorber layer. On the bottom side, the hybrid plasmonic mode in the structure of the optical nanoantenna makes it possible to focus and direct the incoming light on the bottom of the absorber layer and increase the optical pathlengths in the ultra-thin film solar cell. The nanoantenna behavior and three-dimensional finite-difference time-domain analysis show that photon absorptions improve significantly at long wavelength lightwaves through this proposed combined structure. The short circuit current enhancement of the solar cell under 1 sun standard illumination is obtained by a factor of 1.94 and 1.80 for TM and TE polarization of incident light, respectively. Due to the acceptable results for different incident angles and polarizations, ultra-thin thickness, and nano-cuboids synthesis feasibility, our structure has the potential to be applied in the design of miniaturized photovoltaic devices.

Role of metallic nanoparticles in the optoelectronic performance enhancement of InP ultrathin film solar cell

III-V material-based ultrathin Solar Cells (SCs) garnered a great deal of interest due to their benefits such as efficient charge transport, recycling of photons, adaptability, and material usage but suffer from low optical absorption due to thicker active material. In order to increase the optical absorption in the ultra-thin SC, metal nanoparticles (MNPs) are employed that scatter the incident light in the absorber layer resulting in higher optical absorption with the reduced requirement of active material. The role of MNPs in the efficiency improvement of InP SCs has not yet been explored. Therefore, in this paper, we have investigated the impact of plasmonic MNPs of different materials such as gold (Au), silver (Ag) and aluminium (Al) placed on the top of ITO coated 280 nm ultra-thin InP SC with FDTD simulations, which employ the surface plasmon resonance (SPR) to increase the optical absorption by tuning the dimensions of the MNPs. The thickness of InP thin-film and an anti-reflective coating of ITO are optimized to achieve maximum absorption. In addition, the diameter and period of Au, Ag, and Al MNPs are also optimized to achieve higher optical Jsc, and results show that Au nanoparticle with diameter of 50 nm and period of 100 nm shows higher Jsc when compared to Ag and Al nanoparticles of optimized diameter. The device analysis shows the Au nanoparticles placed on the top surface of ITO coated InP ultrathin SC with a power conversion efficiency (PCE) of 22.3% outperform the Ag NPs and Al NPs ITO coated InP ultrathin SC and ITO/InP ultrathin SC without MNPs.

Performance improvement of an ultra-thin film solar cell based on optimized CIGS (Cu(In1-x, Gax)Se2) using appropriate plasmonic nanoparticles

In this paper, the main aim is to improve the absorption and efficiency of an ultra-thin film Cu(InxGa1-x)Se2 (CIGS) solar cell using plasmonic nanoparticles on the back surface of the cell at an optimal molar concentration (X) of the active layer. For this purpose, the effect of changing the molar concentration as well as the key parameters of nanoparticles on the back surface of the cell such as shape, material, size, and period are analyzed. Based on characteristics parameters such as short-circuit current density, open-circuit voltage, fill factor, and power conversion efficiency, the optimal molar concentration for the non-plasmonic cell is 0.4. For the plasmonic case, cubic Ag nanoparticles, with a size of 55 nm and a period of 220 nm, show an improvement of 20.02% and 20.89% for the short-circuit current density and efficiency, respectively. This is due to the near field distribution effect and localized surface plasmon resonance that causes effective scattering of light into the active layer. In addition, for a more detailed analysis of the solar cell performance in the presence of metal nanoparticles, and to investigate the effect of metal oxidation, an Ag2O layer with different thicknesses was added to the optimized Ag nanoparticle.

Numerical modeling of ultra-thin CuSbS2 heterojunction solar cell with TiO2 electron transport and CuAlO2:Mg BSF layers

The ternary chalcostibite copper antimony sulfide (CuSbS2) system, with its very high optical absorption coefficient, low-cost, vacuum-free fabrication techniques, and earth-abundant elements, is a rising candidate as solar absorber material for ultrathin film solar cells. However, due to the Schottky barrier formed at the back-contact and high carrier recombination at the CuSbS2/CdS interface, the efficiency of conventional CuSbS2/CdS heterojunction solar cell is very poor. This article proposes titanium dioxide (TiO2) as an alternative to CdS layer for the CuSbS2-based thin film solar cells (TFSCs). Using TiO2, CuSbS2, and Mg-doped CuAlO2 (CuAlO2:Mg) as an electron transport layer (ETL), absorber layer, and back-surface field (BSF) layer, respectively, a novel (Al/ITO/n-TiO2/p-CuSbS2/p+-CuAlO2:Mg/Au)-based npp+ heterojunction solar cell has been designed and simulated by SCAPS-1D solar cell simulator. The effects of integrating the CuAlO2:Mg BSF layer on the PV responses of the CuSbS2-based heterojunction solar cell in terms of the built-in potential and the back-contact carrier recombination have been studied. In addition, an investigation on the influences of various device parameters viz. carrier concentration and thickness of each layer, back-contact metal work function, shunt and series resistance, and working temperature have been carried out systematically. The results are analyzed in correlation with the PV parameters of the device to optimize the efficiency of the proposed solar cell. The optimized CuSbS2-based solar cell shows good performance stability at high temperature, with a maximum efficiency of 23.05% (Voc = 969 mV, Jsc= 34.61 mA/cm2, FF = 68.71%).

“To Spin or Not to Spin?”—Is Spin‐Coating the Ideal Technique for Pre‐Deposition of Sodium Fluoride for CIGS Rear Surface Passivated Ultrathin Solar Cells?

Herein, using the spin‐coating process as a sodium pre‐deposition technique for Cu(In,Ga)Se2, ultrathin film solar cells is discussed. Throughout this study, several challenges are detected to overcome, such as unevenly deposited salt layers and unplanned clusters (even islands) of sodium salts due to accumulation. The solar cell performances with the optimal and nonoptimal amounts of sodium are shared to assess the effect of varying sodium amounts on performance. The hyperspectral photoluminescence (PL) mapping and imaging and reflection measurements are also used to emphasize the importance of homogeneity of the sodium layer.

Enhanced absorption in thin and ultrathin silicon films by 3D photonic band gap back reflectors

Since thin and ultrathin silicon films have limited optical absorption, we explore the effect of a nanostructured back reflector to recycle the unabsorbed light. As a back reflector, we investigate a three-dimensional (3D) photonic band gap crystal made from silicon that is readily integrated with the thin silicon films. We numerically obtain the optical properties by solving the 3D time-harmonic Maxwell equations using the finite-element method, and model silicon with experimentally determined optical constants. The absorption enhancement spectra and the photonic band gap generated current density are obtained by weighting the absorption spectra with the AM 1.5 standard solar spectrum. We study thin films in two different regimes, much thicker (L Si = 2400 nm) or much thinner (L Si = 80 nm) than the wavelength of light. For L Si = 2400 nm thin film, the 3D photonic band gap crystal enhances the spectrally averaged (λ = 680 nm to 880 nm) silicon absorption by 2.22 × (s −pol.) to 2.45 × (p −pol.), which exceeds the enhancement of a perfect metal back reflector (1.47 to 1.56 ×). The absorption is considerably enhanced by the (i) broadband angle and polarization-independent reflectivity in the 3D photonic band gap, and (ii) the excitation of many guided modes in the film by the crystal’s surface diffraction leading to greatly enhanced path lengths. For L Si = 80 nm ultrathin film, the photonic crystal back reflector yields a striking average absorption enhancement of 9.15 ×, much more than 0.83 × for a perfect metal. This enhancement is due to a remarkable guided mode that is confined within the combined thickness of the ultrathin film and the photonic crystal’s Bragg attenuation length. An important feature of the 3D photonic band gap is to have a broad bandwidth, which leads to the back reflector’s Bragg attenuation length being much shorter than the silicon absorption length. Consequently, light is confined inside the thin film and the remarkable absorption enhancements are not due to the additional thickness of the photonic crystal back reflector. We briefly discuss a number of high-tech devices that could profit from our results, including ultrathin film solar cells.

Distributed silicon nanoparticles: an efficient light trapping platform toward ultrathin-film photovoltaics.

In this paper, a new architecture comprising silicon nanoparticles inside a hole transport layer laid on a thin silicon layer is proposed to develop ultrathin film solar cells. Using generalized Mie theory, a fast analytical approach is developed to evaluate the optical absorption of the proposed structure for various geometries, polarizations and angles of incidence. The analytical results are verified through comparison with full-wave simulations, illustrating a reasonable agreement. The electrical performance of a distributed silicon nanoparticle solar cell is determined for selected configurations. To be able to predict the light-trapping in a solar cell comprising randomly distributed nanospheres, a new technique based on probability theory is developed and validated through comparison with the simulation results. Both analytical and numerical results show that the excited Mie resonant modes in the proposed structure lead to a significant enhancement in both absorption and the photo-generated current, in comparison to a conventional silicon solar cell with an equivalent volume of the active layer. In the case of random distributions, other advantages, including the simple fabrication process, indicate that the cell is a promising structure for ultrathin photovoltaics.

High-efficiency ultra-thin Cu2ZnSnS4 solar cells by double-pressure sputtering with spark plasma sintered quaternary target

In recent years, Cu2ZnSnS4 (CZTS) semiconductor materials have received intensive attention in the field of thin-film solar cells owing to its non-toxic and low-cost elements. In this work, double-pressure sputtering technology is applied to obtain highly efficient and ultra-thin (~450 nm) pure Cu2ZnSnS4 (CZTS) solar cell. Using mixed materials with sulfides and copper powder as a quaternary target via spark plasma sintering (SPS) method and adopting double-layer sputtering (high + low pressure), a highly adhesive and large-grained CZTS thin film is achieved. As a result, the damage to the surface of Mo contact is decreased so that the reflectivity of incident light can be improved. Moreover, the composition of CZTS film was more uniform and the secondary phase separation at the Mo interface was reduced. Therefore, the interface defect state and deep level defect density in corresponding device with double-pressure is reduced and the ratio of depletion thickness to absorption layer thickness can reached to 0.58, which promoted the collection of photogenerated carriers. Finally, an efficiency of 9.3% for ultra-thin (~450 nm) CZTS film solar cell is obtained.

Light absorption enhancement in ultrathin film solar cell with embedded dielectric nanowires

A novel design of thin-film crystalline silicon solar cell (TF C-Si-SC) is proposed and numerically analyzed. The reported SC has 1.0 µm thickness of C-Si with embedded dielectric silicon dioxide nanowires (NWs). The introduced NWs increase the light scattering in the active layer which improves the optical path length and hence the light absorption. The SC geometry has been optimized using particle swarm optimization (PSO) technique to improve the optical and electrical characteristics. The suggested TF C-Si-SC with two embedded NWs offers photocurrent density ({J}_{ph}) of 32.8 mA cm−2 which is higher than 18 mA cm−2 of the conventional thin film SC with an enhancement of 82.2%. Further, a power conversion efficiency of 15.9% is achieved using the reported SC.

Large area and low-cost nanoholes-based plasmonic back reflector fabricated by a simple nanofabrication technique for photovoltaics applications

Plasmonic back reflectors (PBRs) are employed in thin film and ultra-thin film solar cells to increase their optical thickness and energy conversion efficiency. Here, we report a wet-chemical etching based nanofabrication technique to prepare large area and low-cost nanoholes-based plasmonic back reflectors (n-PBRs). The n-PBR is a 150 nm thick Ag thin film embedded with random nanoholes with varying structure and morphology. We successfully incorporated the n-PBR into a standard a-Si:H thin film solar cell built on a randomly textured FTO substrate; the textured FTO serves as both the front contact and light-entry side light trapping medium. Three n-PBRs each with different density of random nanoholes were studied. All the plasmonic a-Si:H solar cells with n-PBRs exhibited an optical absorption enhancement in the spectrally intense 550–800 nm wavelength range with an overall enhancement factor of 1.1 and a maximum enhancement factor of 1.3 in the 720–780 nm wavelength range. The n-PBRs produced a haze of 65% in the 700–800 wavelength range. The hazy back contact effectively scatters the unabsorbed light back into the active medium of the solar cell with increased path length and hence, contributes to the enhanced absorption in the solar cell. The method of nanofabrication reported here to produce plasmonic back reflectors can be easily adopted into commercial fabrication of various types of solar cells including ultrathin inorganic and organic, polymer, perovskite and dye-sensitized solar cells to enhance their energy conversion efficiency without adding any cost/watt to the solar cells.

Production and photovoltaic characterisation of n-Si/p-CZTS heterojunction solar cells based on a CZTS ultrathin active layers

In this study, Au/n-Si/p-CZTS/Ag solar cells have been produced by using PLD technique. Ultrathin CZTS films have been grown on n-Si wafer in different thicknesses depending on number of laser pulses. These ultrathin CZTS films were analysed by XRD, AFM and UV–vis spectra. J–V characteristics of Au/n-Si/p-CZTS/Ag solar cells have been determined based on thickness of ultrathin CZTS films under AM 1.5 solar radiation of 80 mW/cm2. Short circuit current density (mA/cm2), fill factor, open circuit voltage (V) and power conversion efficiency (%) of ultrathin CZTS film solar cells have been determined for device produced in this work. The photovoltaic (PV) characteristics of ultrathin CZTS film solar cells has been discussed in detail in this present article and, as a result, the ideal ultrathin CZTS film solar cell structure having the highest efficiency has been determined and concluded.

Efficient Light Management in Ultrathin Crystalline GaAs Solar Cell Based on Plasmonic Square Nanoring Arrays

Improving the photon absorption in ultrathin-film solar cells with active layer thickness of a few micrometers is important for enhancing efficiency and reducing cost. We present a computational study of novel design consisting of ultrathin absorber layer made of gallium arsenide (GaAs) integrated with plasmonic square nanoring particles. The energy absorbed by GaAs layer is significantly enhanced with the help of plasmonic nanorings, resulting in substantial absorption enhancement of approximately 34% compared with bare active layer. For qualitative analysis, the short-circuit current density of thin-film cell is evaluated for AM 1.5 G solar illumination and is found to be 1.4 times higher compared with unpatterned solar cell structure. Furthermore, the structure is optimized by varying different parameters and materials of functional layers, yielding a photocurrent density of 30.185 mA/cm2, which is close to the Yablonovitch limit.

Performance enhancement methods of an ultra-thin silicon solar cell using different shapes of back grating and angle of incidence light

The goal of this research is to evaluate the efficiency dependence of a silicon based ultra-thin film solar cell on angle of incident of light. Here, the optical path length of incoming light inside the active layer is increased using a distributed Bragg reflector (DBR) and a rectangular, triangular or cylindrical shaped grating horizontally arranged and place on top of DBR. This arrangement of DBR and horizontal grating is used to control the light inside the absorber. It is shown that by implementing these structures, it is possible to enhance the efficiency of a 3 µm thin silicon solar cell near up to %20. In addition, when incidence angles of 0°–30° are considered, it is learned that cylindrical shaped backside reflector, when is combined with the DBR results in best efficiency.

Quantum-kinetic perspective on photovoltaic device operation in nanostructure-based solar cells

Abstract