Optical Properties Of Solar Cells Research Articles

Implementation of various colors in Cu(In,Ga)Se2 thin-film solar cells by diffractive nanostructures

With the increasing use of building-integrated photovoltaic technology, it has become necessary for solar panels to blend in with their surroundings. Diffractive nanostructures can be used to reduce optical losses and create colorful solar cells. To make colors on Cu(In,Ga)Se2 (CIGS) thin-film solar cells, we fabricated diffractive nanostructures by using nanoscale imprinting and transfer lithography methods. And we investigated how the material types and pattern shapes of the nanostructures influence the optical properties of solar cells, such as the short-circuit current density (JSC), coordination of color appearance, and color quality. We used two types of pillars and grating nanostructures of SiO2 and TiO2 layers on CIGS thin-film solar cells to produce various colors. The SiO2 demonstrated an increase in JSC without significant loss of color quality compared to TiO2. By utilizing a hexagonally arrayed pillar pattern, colors are observed at various angles on an axis different from the incident light, unlike colors observed only at a single angle in the grating structure. The nanoimprinting lithography process allowed us to produce high-quality nanostructures on both rigid glass and flexible stainless-steel substrates.

Adjustment of the eccentricity and random distribution of embedded ellipsoidal Ag nanoparticles to boost optical properties of PSC

Both the shape and distribution of embedded plasmon nanoparticles within the absorption layer are crucial factors affecting the optical properties of solar cells significantly. Herein, by employing a finite element method (FEM), we proposed a perovskite solar cell (PSC) by introducing a layer of position-randomly-distributed (PRD) ellipsoidal Ag nanoparticles in the CH3NH3PbI3thin film as they provide prototype nanoparticles encountered in experiments. The corresponding absorption spectra and photocurrent were calculated and optimized as a function of both their eccentricity and coverage, which are elucidated well in terms of their EM distributions. The maximum photocurrent is revealed to reach 22.68 mA/cm2, which is 1.18 times larger than that of planar reference. The present work is believed to be insightful for further boosting the optical efficiency of PSCs and easy of choosing appropriate coverage ratio and eccentricity of the embedded ellipsoidal Ag nanoparticles.

Study of electron paramagnetic resonance as a tool to discriminate between boron related defects in barium disilicide

Barium disilicide (BaSi2), composed of Earth-abundant and nontoxic elements, is a promising material for thin-film solar cells. The control of carrier type and carrier concentration by impurity doping is particularly important for the application of BaSi2 to solar cells. However, the presence of defects in semiconductors such as BaSi2 may have a significant impact on the electrical and optical properties of solar cells. In this study, we chose boron to act as a p-type impurity in BaSi2 and studied boron-related defects using the Quantum Espresso method with density functional theory. The formation energy of interstitial boron defects was found to be lower than that of boron in Si vacancy sites. The hyperfine coupling constants of 137Ba with antisite boron defects (BSi) are very localized and differ significantly from those of 137Ba with interstitial boron defects (Bi). This suggests that neutral BSi and Bi can be identified by electron paramagnetic resonance.

Determining the optical properties of solar cells using low cost scanners

This paper investigates the use of consumer flatbed scanners for the use of monitoring solar cell precursors. Two types of scanners are investigated a contact image scanner and scanners with more conventional optical setups. The contact image sensor is found to be more suitable as it does not require additional flat field calibration. The scanners’ ability to monitor variation in sample texture was investigated by monitoring the reflection of multi-crystalline and mono-crystalline textured wafers. For a baseline, a comparison was made to a high-end tool used in industry. Both good qualitative agreement and statistical correlation were achieved between the scanner and industry tool for the isotropic multi-crystalline wafers.

A new and simple method for simulation of lattice mismatch on the optical properties of solar cells: A combination of DFT and FDTD simulations

Since controlling strain in different types of heterostructures devices causes the improvement of properties and functionalities in real devices, considering this matter is vital in simulation. In this paper, the impact of strain in the interface of different layers of solar cells has been investigated with density functional theory (DFT) and finite-difference time-domain (FDTD) techniques. We have simulated the complex issue of strain and relaxation of atomic layers by using a new, effective and simple method and using a precise meshing technique. The amplitude and region of the strain have been meshed to specific values. The lattice strain is included in both simple and gradient patterns in the theoretical simulations. The strain factor has been considered in two steps; between active layers in solar cells and between the active layer and the electron transport layer (ETL). DFT results indicate alterations in the structural and optical properties of the material as a function of strain. The results of DFT have been used in FDTD simulation. To describe this new method, we used perovskite as the active layer in the solar cell. We realized that the electric and optical parameters such as short circuit current density, absorptance, and reflectance of strained solar cells are different in comparison to strain free cells, and applying strain to the contacting layers in the solar cell alters the optoelectronic properties of the device.

All-round performance improvement of semitransparent perovskite solar cells by a pressure-assisted method

A pressure-assisted method was used to achieve a remarkable enhancement in the crystallinity and flatness of ultra-thin MAPbI3 films. This process facilitates an all-round improvement in the photoelectric and optical properties of solar cells.

Exploring optical properties of solar cells by programming and modeling

One of the main factors influencing the efficiency of solar cells is their optical properties. So, most light is reflecting back and transmit through solar cell. This leads to a decrease in the efficiency. We know that the refractive index of silicon is 3-4 depending on the wavelength of light, and the refractive index of air is about 1. This causes to reflect 34 percentages of the incident light. To reduce the amount of reflected light, the surface of the solar cell should be covered with an anti-reflection layer. It is important to determine the conditions of the types and thicknesses of the material covering the surface of the solar cell. Semiconductor devices modeling has become very popular. Because the results obtained through modeling are very close to the experimental results. In this study, we also modeled the solar cell with and without an anti-reflective layer using the Sentaurus TCAD software package and presented the results obtained. A new program was developed using the C # programming language, and a library was developed to help new researchers study the optical properties of solar cells directly for that program, and a number of results were obtained.

Exploring optical properties of solar cells by programming and modeling

Exploring optical properties of solar cells by programming and modeling

Recent Developments of Solar Cells from PbS Colloidal Quantum Dots

PbS (lead sulfide) colloidal quantum dots consist of crystallites with diameters in the nanometer range with organic molecules on their surfaces, partly with additional metal complexes as ligands. These surface molecules are responsible for solubility and prevent aggregation, but the interface between semiconductor quantum dots and ligands also influences the electronic structure. PbS quantum dots are especially interesting for optoelectronic applications and spectroscopic techniques, including photoluminescence, photodiodes and solar cells. Here we concentrate on the latter, giving an overview of the optical properties of solar cells prepared with PbS colloidal quantum dots, produced by different methods and combined with diverse other materials, to reach high efficiencies and fill factors.

Enhancing Charge Transfer and Photoelectric Characteristics for Organic Solar Cells

The main purpose of this work is to analyze the effect of steric hindrance on the photoelectric performance of three different donor sensitizers (ZHG5, ZHG6, and ZHG7) by molecular theory simulation engineering. Photoelectric physical and photoelectric chemical parameters are investigated by means of frontier molecular orbital, global reactivity descriptors, optical absorption properties, fluorescent lifetime, charge density difference, and influence of external electric field. The results showed that the performance of the quinoxaline sensitizer was deteriorated by gradually increasing the steric hindrance to auxiliary donors. The optical properties of the hybridization of cir-coronene graphene quantum dot (GR) with the three dyes have been revealed, and the results show that graphene quantum dots can indeed improve the optical properties of solar cells. In addition, nine new molecules were designed by inserting six functional groups; it is found that inserting -CN in the acceptor part of the molecular structure is beneficial to the performance of the sensitizer.

Degradation characteristics of electron and proton irradiated InGaAsP/InGaAs dual junction solar cell

The degradation characteristics of MOCVD grown InGaAsP/InGaAs dual junction solar cells, irradiated by 1 MeV electron, 3 MeV and 10 MeV proton, have been investigated. Main electrical and optical properties of solar cell degraded seriously with the increase of irradiation fluences due to the irradiation induced defects which are acting as non-radiative recombination centers in the active layers of the solar cell. The remaining factor of Pmax is 0.67, 0.53 and 0.51 for 1 MeV electron, 10 MeV proton, and 3 MeV proton irradiation, respectively, when the displacement damage dose (DDD) is 3.16×1010 MeV/g. The degradation of external quantum efficiency (EQE) of each subcell mainly occurred in the long wavelength region, the integrated current density Jsc of InGaAsP and InGaAs subcells degraded more seriously upon 3 MeV and 10 MeV proton irradiation comparing to 1 MeV electron irradiation. The InGaAsP subcell turned out to be the current limiting unit due to the lower Jsc before and post irradiation. By applying equivalent displacement damage dose model, the relative damage coefficient for 3 MeV proton to 10 MeV proton and 1 MeV electron to 10 MeV proton have been calculated.

Second-Order Nonlinear Optical Switch Manipulation of Photosensitive Layer by an External Electric Field Coupled with Graphene Quantum Dots.

The main purpose of this work is to explore the effect of graphene quantum dots (GR) filling the photosensitive layer. The multibranched dye JH-1 as the photoactive layer material was used to analyze the non-negligible role of graphene quantum dots from the perspectives of optimized structure, electrochemical parameters, optical properties, nonlinear optical (NLO) switch, and external electric field. The results demonstrated that the graphene quantum dots not only improve the optical properties of solar cells but also control the electron transfer in the photosensitive layer molecules under the manipulation of a specific external electric field. When the external electric field intensity is below 20 × 10-4 au, the excess electron orbital does not change. When the external electric field reaches 25 × 10-4 au, the excess electron orbital on the graphene quantum dots evolves. This discovery allows the electron transfer from the photosensitive layer, which should be controlled by the NLO switch. In addition, the optical properties of sensitizers showed regular evolution in the external electric field, which provides an effective way to improve the performance. Comprehensive analysis indicated that the doping of graphene quantum dots with the photosensitive layer can be used as a new way to improve the photoelectric conversion efficiency of solar cells.

Photonic Structures for Light Trapping in Thin Film Silicon Solar Cells: Design and Experiment

One of the foremost challenges in designing thin-film silicon solar cells (TFSC) is devising efficient light-trapping schemes due to the short optical path length imposed by the thin absorber thickness. The strategy relies on a combination of a high-performance back reflector and an optimized texture surface, which are commonly used to reflect and scatter light effectively within the absorption layer, respectively. In this paper, highly promising light-trapping structures based on a photonic crystal (PC) for TFSCs were investigated via simulation and experiment. Firstly, a highly-reflective one-dimensional photonic crystal (1D-PC) was designed and fabricated. Then, two types of 1D-PC-based back reflectors (BRs) were proposed: Flat 1D-PC with random-textured aluminum-doped zinc oxide (AZO) or random-textured 1D-PC with AZO. These two newly-designed BRs demonstrated not only high reflectivity and sufficient conductivity, but also a strong light scattering property, which made them efficient candidates as the electrical contact and back reflector since the intrinsic losses due to the surface plasmon modes of the rough metal BRs can be avoided. Secondly, conical two-dimensional photonic crystal (2D-PC)-based BRs were investigated and optimized for amorphous a-SiGe:H solar cells. The maximal absorption value can be obtained with an aspect ratio of 1/2 and a period of 0.75 µm. To improve the full-spectral optical properties of solar cells, a periodically-modulated PC back reflector was proposed and experimentally demonstrated in the a-SiGe:H solar cell. This periodically-modulated PC back reflector, also called the quasi-crystal structure (QCS), consists of a large periodic conical PC and a randomly-textured Ag layer with a feature size of 500–1000 nm. The large periodic conical PC enables conformal growth of the layer, while the small feature size of Ag can further enhance the light scattering. In summary, a comprehensive study of the design, simulation and fabrication of 1D-PC- and 2D-PC-based back reflectors for TFSCs was carried out. Total absorption and device performance enhancement were achieved with the novel PC light-trapping systems because of their high reflectivity or high scattering property. Further research is necessary to illuminate the optimal structure design of PC-based back reflectors and high solar cell efficiency.

Formation of silicon carbide by laser ablation in graphene oxide-N-methyl-2-pyrrolidone suspension on silicon surface

Laser ablation of a silicon wafer in graphene oxide-N-methyl-2-pyrrolidone (GO-NMP) suspension was carried out with a pulsed Nd:YAG laser (pulse duration=250ns, wavelength=1064nm). The surface of silicon wafer before and after laser ablation was studied using optical microscopy, scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). The results showed that the ablation of silicon surface in liquid by pulsed laser was done by the process of melt expulsion under the influence of the confined plasma-induced pressure or shock wave trapped between the silicon wafer and the liquid. The X-ray diffraction‌ (XRD) pattern of Si wafer after laser ablation showed that 4H-SiC layer is formed on its surface. The formation of the above layer was also confirmed by Raman spectroscopy, and X-ray photoelectron spectroscopy‌ (XPS), as well as EDX was utilized. The reflectance of samples decreased with increasing pulse energy. Therefore, the morphological alteration and the formation of SiC layer at high energy increase absorption intensity in the UV‌–vis regions. Theoretical calculations confirm that the formation of silicon carbide from graphene oxide and silicon wafer is considerably endothermic. Development of new methods for increasing the reflectance without causing harmful effects is still an important issue for crystalline Si solar cells. By using the method described in this paper, the optical properties of solar cells can be improved.

Angular matrix framework for light trapping analysis of solar cells.

Complex light trapping structures make it challenging to simulate the optical properties of solar cells accurately. In this paper, a framework is proposed where matrices are used to describe the transition of the angular distribution of the light when it is reflected, transmitted or absorbed. The matrices can be computed using a range of different simulation methods and when parts of a complex structure are to be optimized, or the incident light is altered, the pre-computed matrices can be used with the potential benefit of saving computational time. The optical properties of silicon wafers with different texturing, surface coatings and light incident angles were simulated and compared with measurements to demonstrate the accuracy of the proposed framework. It is shown that different simulation methods can be effectively integrated to model different parts of the solar cell and structures with multiple coherent and incoherent layers. These features enable efficient and rapid evaluation of the optical properties of the device as a function of its physical properties.

The optical properties of solar cells before and after encapsulation

In this work we investigate how the optical properties of monocrystalline silicon and polycrystalline silicon wafers are affected by texturing techniques and encapsulation. For monocrystalline wafers, the KOH etching is better than acid etching while reactive ion etching (RIE) is proven to be preferred compared to acid etching for polycrystalline wafers. The differences in reflectance (R) between two textures are apparent before encapsulation, but when the textured wafers are encapsulated with glass especially antireflectance coated (ARC) glass, the difference can be reduced from about five percentage points to below a percentage point. More important, the optical losses caused by reflectance (R) losses and parasitic absorption losses (A) for four types of commercial monocrystalline and polycrystalline silicon module are quantified and compared. Analyses are carried out for eight configurations using a stratified model consisting of solar cell wafers as well as cover glass and ethylene vinyl acetate (EVA). The model is to first obtain the external reflectance (R) and transmittance (T) in each layer, and the spectrally parasitic absorption loss associated with the cover glass and EVA is calculated with the aid of R and T measurements, which allows us to do a complete optical loss analysis for the solar module. The results show that the KOH texture with ARC glass encapsulation may be better choice for monocrystalline wafers, which gives a 94.04% of effective light collected by silicon. The RIE technique with ARC glass is suitable for polycrystalline substrates with excellent light trapping of 94.14%. After all, reflectance from glass surface and silicon surface accounts for over 70% of total loss, while the absorption of glass and EVA accounts for the rest and less loss.

Optimization of a-Si1–xGex:H single-junction and a-Si:H/a-Si1–xGex:H tandem solar cells with enhanced optical management

This work aimed at improving the optical management of a-Si:H/a-Si1–xGex:H tandem cells and a-Si1–xGex:H single-junction cells. To improve the optical management, the effects of the a-Si1–xGex:H bandgap, the bandgap graded absorber and the n-type μc-SiOx:H back reflecting layer on the cell performance were investigated. Optical reflection spectra, internal quantum efficiency, external quantum efficiency (EQE), and cell performance were used to evaluate the improvement of the optical properties of solar cells. The tandem cells with a-Si1–xGex:H bandgap of 1.53 eV exhibited sufficient optical absorption from 630 to 900 nm and thus lead to higher JSC. Second, the EQE of a-Si1–xGex:H single-junction cell was significantly enhanced from 630 to 720 nm by employing bandgap graded absorber that relatively improved the JSC by 3.8% despite that the reduction in EQE from 720 to 900 nm compared to the cell without bandgap grading. Moreover, the μc-SiOx:H(n)/Ag back reflector showed higher optical reflection than a-Si:H(n)/Ag did, which relatively improved the JSC by 12.3%. The cell with μc-SiOx:H(n)/Ag back reflector exhibited a comparable JSC and efficiency to the cell with ITO–Ag. The previously mentioned approaches are relevant to enhance the optical management in cells and can be applied to silicon-based thin-film solar cells.

Effects of InGaN/GaN superlattice absorption layers on the structural and optical properties of InGaN solar cells

This article studies metal-organic vapor phase epitaxy-grown InGaN p-i-n solar cells with superlattice (SL) absorption layers on c-plane sapphire for the influence of InGaN/GaN SLs on the structural and optical properties of the solar cells. Numerical simulations indicate that conventional p-i-n solar cells with a 200-nm-thick In0.06Ga0.94N absorption layer provide absorption rates as high as 65%. However, experimentally, the optical properties of such an epistructure are deteriorated by the formation of structural defects and result in the fabricated devices having worse photovoltaic characteristics. On the other hand, high-resolution x-ray diffraction and photoluminescence analyses show that solar cells with a SL have improved crystalline quality and can accommodate more indium content than those using an InGaN layer. It was also found that the degree of the exciton localization effect does not rise considerably with increases in the indium content and the SL pair numbers. This could be due to variations in dislocation density, interface roughness, and well width during the SL growth. Using SLs of a reasonable crystalline quality, these fabricated solar cells exhibit improved photovoltaic characteristics.