Front Surface Of Solar Cell Research Articles

Effective index model as a reliable tool for the design of nanostructured thin-film solar cells

Nanostructured anti-reflection coatings (ARC) are used to reduce the reflectivity of the front surface of solar cells. Computational electromagnetism helps to evaluate the spectral reflectivity of of this type of ARC using several approaches. They typically require large computational resources both in time and hardware elements (memory allocation, speed of processors, etc.). Long computational times may jeopardize optimization processes based on the iterative evaluation of a given merit function that depends on several parameters. Then, simplified analytic methods can speed up this evaluation with moderate computational resources. In this contribution we adapt an Effective Index Model (EIM) to the case of the design of an ARC made with nanoparticles (NP) embedded in a medium at the front surface of a thin-film silicon solar cell. Our approach modifies the discrete dipole approximation method to adapt it to the geometric and material properties of the NPs. The results obtained from the analytic method are compared with those evaluated through a Finite Element Method (FEM) for several cases involving variations in the size and geometry of the NP arrangement, obtaining reflectances that differ less than 10% for the worst case analyzed but bieng about 100 times faster than the FEM.

Record Photocurrent Density over 26 mA cm−2 in Planar Perovskite Solar Cells Enabled by Antireflective Cascaded Electron Transport Layer

Planar perovskite solar cells (PSCs) hold promise for simple processing at low temperatures; however, they usually show lower short‐circuit current density (Jsc) than their mesoporous counterparts owing to their higher primary optical reflection losses at the front side. The antireflective nature of a mesoporous electron transport layer (ETL) enables a low optical reflection in the front surface of solar cells, which is challenging to realize in planar PSCs. Herein, an antireflective cascaded ETL structure using SnO2/TiO2–Cl bilayers is devised to reduce optical reflection losses and to improve electrical performance in planar PSCs. The antireflective cascaded ETL results in an enhanced Jsc of 25.4 mA cm−2 in formamidinium lead triiodide based planar PSCs, compared with the control Jsc of 24.6 mA cm−2 using single‐layered SnO2 ETL. A record‐high Jsc of 26.1 mA cm−2 is further achieved using an additional antireflective coating on the front glass side, leading to a power conversion efficiency of 22.9%.

Single material TiO2 thin film by atomic layer deposition for antireflection and surface passivation applications on p-type c-Si

A thin film deposited on the front surface of solar cell plays an important role in reducing the reflection of incident light and providing surface passivation. Although ultrathin TiO2 films have shown excellent performance of surface passivation, simultaneously serving both functions is hindered by the crystallization issue, which can degrade the passivation quality of TiO2 film, as the film thickness is over certain value (few nanometer only). Here we showed that both functions can be satisfied by single material of titanium oxide film through atomic layer deposition at low temperatures. By varying deposition temperatures from 80 to 200 °C, the TiO2 film deposited at 80 °C can maintain its amorphous phase up to the thickness of 114 nm. In addition, the optimal thickness for antireflection calculated by OPAL 2 is 61 nm, meaning that amorphous TiO2 film to provide antireflection and surface passivation can be achieved. The passivation quality is verified by minority carrier lifetime measurement using photo-conductance decay method and presented the ultralow surface recombination velocity of 8.7 cm/s. Furthermore, the passivation mechanism is investigated by X-ray diffraction (XRD) and secondary ion mass spectroscopy (SIMS), in which the absence of crystalline issue is confirm and both chemical passivation (due to H termination) and field effect passivation (due to residual Cl atoms) are associated with the improvement of passivation quality. A post deposition anneal is conducted on the TiO2 film deposited at 80 °C. The results present that extra thermal budgets can ruin the passivation quality, which is explicated by the TiO2 crystallization as the temperature exceeding 350 °C from the XRD measurements, and by the descending of Cl atom (also field effect passivation) as increasing of the annealing temperature from the SIMS measurements.

Optimization and Modeling of Antireflective Layers for Silicon Solar Cells: In Search of Optimal Materials

Depositing an antireflection coating on the front surface of solar cells allows a significant reduction in reflection losses. It thus allows an increase in the efficiency of the cells. A modeling of the refractive indices and the thicknesses of an optimal antireflection coating has been proposed. Thus, the average reflective losses can be reduced to less than 8% and less than 2.4% in a large wavelength range respectively for a single-layer and double-layer anti-reflective coating types. However, the difficulty of finding these model materials (materials with the same refractive index) led us to introduce two notions: the refractive index difference and the thickness difference. These two notions allowed us to compare the reflectivity of the antireflection layer in silicon surface. Thus, the lower the refractive index difference is, the more the material resembles to the ideal material (in refractive index), and thus its reflective losses are minimal. SiNx and SiO2/TiO2 antireflection layers, in the wavelength range between 400 and 1100 nm, have reduced the average reflectivity losses to less than 9% and 2.3% respectively.

Investigations of III–V concentrator solar cells with liquid immersion for high concentrating photovoltaic systems

Liquid-immersed III–V concentrator solar cells have been proposed either for providing a new concentrator with high optical performance or for solving the receiver thermal management issue under high concentration. In this paper, the behavior of III–V GaInP/GaInAs/Ge triple junction (TJ) solar mini-receivers immersed in white oils A/B/C, C14 n-alkane, C16 iso-alkane, and dimethyl silicone oil, respectively, is examined. A sizeable relative percentage increase (4.67–8.99%) in electrical conversion efficiency of TJ solar mini-receivers is found for 4-mm-thick liquid layers. Increasing the thicknesses of all the liquid candidates to approximately 9–10 mm continues to raise the efficiency of the corresponding TJ solar mini-receivers. The optical effect and the electrical effect contributing to the increase in efficiency, which is caused by the thin liquid layer on the solar cell front surface, are discussed. Further, to evaluate the durability of TJ solar mini-receivers operating in the examined liquids, UV exposure, damp heat, and step temperature accelerated lifetime tests on the liquid-immersed TJ solar mini-receivers were carried out. Results from the tests demonstrate the long-term stability of TJ solar mini-receivers operated in C14 n-alkane, C16 n-alkane and dimethyl silicone oil, respectively. They also indicate that among these the best liquids for immersing III–V concentrator solar cells is dimethyl silicone oil, followed by C14 n-alkane.

Optimizing front metallization patterns: Efficiency with aesthetics in free-form solar cells

Free-form solar cells are cells of unconventional shapes (e.g. hexagonal, leaf-shaped etc). Their flexible shape adds to the aesthetics of the surroundings as well as allows to place them over objects where conventional solar cells might not fit. Evidently, these cells need to be efficient as well, and one of the important factors that controls their performance is the front metallization design. In this paper, we present the application of topology optimization (TO) to optimize the front metallization patterns for free-form solar cells. TO distributes the electrode material on the solar cell front surface in an efficient manner, such that the total power output is maximized. To demonstrate the capability of the proposed methodology, we use it to optimize front metal grids for several complex solar cell shapes e.g. circular, hexagonal, leaf-shaped, motorbike fairings, etc. The results presented here demonstrate the capability of TO to generate efficient designs for these free-form shapes.

Numerical simulation of light absorption enhancement in microcrystalline silicon solar cells with Al nanoparticle arrays

Metal nanoparticles with low cost and high performance have good potential applications in light-trapping of solar cells. In this paper, a three-dimensional model is proposed to simulate the light absorption of microcrystalline silicon (μc-Si:H) thin film solar cells. The effects of spherical and hemispherical Al nanoparticle arrays located on the front surfaces of solar cells are investigated, and the particle radius and array period are optimized by the finite element method. The results show that the optimal Al nanoparticle arrays can enhance broadband absorption in thin film solar cells. For spherical particle arrays, the key parameter that influences light absorption in solar cells is period/radius ratio (P/R) or particle surface coverage. When P/R=4-5, the optimum integrated absorption enhancement (Eabs) is over 20% under AM1.5 illumination compared with the solar cell without nanoparticles. The value of Eabs is small and decreases with the increase of P/R when P/R>5, and Eabs is less than zero when P/RP=500 nm and R=120 nm, the spectral absorption rate as a function of wavelength shows broadband absorption including four distinct peaks, which are attributed to quadrupole plasmon resonance mode, dipole resonance mode and waveguide mode respectively according to the electric field distribution in the solar cell. For hemispherical particle arrays, the maximum value of Eabs is 24.5%, which is higher than that of the solar cell with optimized spherical particle arrays. This is due to the high coupling efficiencies of the particles, so that most of the scattered light is directly coupled into the substrate. However, the value of Eabs is very sensitive to the hemispherical particle radius. As the radius decreases, the scattering cross-section and scattering efficiency of the particle decrease dramatically. As the radius increases, the dipole plasmon resonance wavelength rapidly shifts towards longer wavelength (red shift). Both of these are detrimental to absorption enhancement of solar cells. Thus we conclude that spherical Al particle arrays are more preferable in actually fabricating the light-trapping of solar cells.

Mass production of Si quantum dots for commercial c-Si solar cell efficiency improvement

An approach to mass producing Si quantum dots (QDs) based on a controlled chemical etching process is developed. Si ultrafine powders in methanol are oxidized and etched consecutively, followed by sequential filtering. Si QDs thus obtained are well dispersive and uniform in size, and are applied to improving commercial c-Si solar cell performance by depositing Si QD-contained SiO2 sol–gel on the front surface of solar cell. A maximal relative efficiency enhancement of 3.93% is achieved after Si QD concentration optimization, and the photoelectric conversion efficiency increases from 18.05% to 18.76% via photoluminescence conversion of Si QDs.

On the application of thin films of silicon nanoparticles for increasing solar cell efficiency

The effect of thin films of silicon nanoparticles (nc-Si), deposited onto the front surface of single-crystal silicon solar cells, on their conversion efficiency is studied. The thin films are grown using non-luminescent silicon nanoparticles with an average diameter of 12 nm with SiO x (0 ≤ x ≤ 2) shells and silicon nanoparticles 2 nm in diameter with organic shells of octadecene, which exhibit photoluminescence in the red spectral region. It was found that nc-Si film deposition increases the solar-cell conversion efficiency by 12% with respect to the initial value. An analysis of the current-voltage characteristics and reflectance spectra of solar cells allows the conclusion that the increase in the conversion efficiency is controlled by the passivation of defects on the front surface of the solar cell by nanoparticles and a decrease in the light reflectance of this surface.

태양전지 모듈의 구성 요소가 PID 발생에 미치는 영향

PID (potential induced degradation) of PV module is the degradation of module due to the high potential difference between the front surface of solar cells and ground when PV modules operate under high humidity and temperature conditions. PID is generally derived from the positive sodium ions in front glass that are accumulated on P-type solar cells. Therefore, some papers for the electrical characteristic of only front components as glass, EVA sheet, solar cell under PID generation condition were revealed. In this paper, we analyzed the different outputs of module with PID by considering the all parts of module including the back side elements such as glass, back sheet. Mini modules with one solar cell were fabricated with the various parts on front and back sided of module. To generate PID of module in a short time, the all modules were applied.1,000 V in , 85% RH. The outputs, dark IV curves and EL images of all modules before and after experiments were also measured to confirm the main components of module for PID generation. From the measured results, the outputs of all modules with front glass were remarkably reduced and the performances of modules with back and front glass were greatly deteriorated. We suggest that the obtained data could be used to reduce the PID phenomenon of diverse modules such as conventional module and BIPV (building integrated photovoltaic) module.

Optimization of plasmonic cavity-resonant multijunction cells

Improving spectral photon harvesting is important for thin-film multijunction cells. We show that efficient spectral flux management can be achieved using genetic algorithm-optimized surface plasmon (SP) cav- ity-resonant type multijunction cells. We also observe that the excitation of the SP quasi-guided mode, Fabry-Perot mode, and SP polariton signifi- cantly enhance the photocurrent of multijunction cells. Two types of cavity structures are investigated. For the optimized SP intermediate reflector and bottom-grating cavity, the resonant cavity mode efficiently increases the long-wavelength absorption in the bottom cell by 63.27%, resulting in reduced absorbance asymmetry between the top and the bottom cells. Accordingly, the matched integrated absorbance is increased by 14.92%. For the optimized SP top- and bottom-grating (TBG) cavity, the integrated absorbance and current matching are improved due to the higher transmission through the solar cell front surface and the exci- tation of the quasi-guided mode with a more localized field in the bottom cell. The matched integrated absorbance is improved by 85.68% for the TBG cavity. © 2013 Society of Photo-Optical Instrumentation Engineers (SPIE) (DOI: 10

Characterization of 2-D reflection pattern from textured front surfaces of silicon solar cells

Reflected light from textured front surfaces of a solar cell contains useful information about the surface geometry as well as the optical properties of the cell. In this study, the 2-D reflected light distributions from front surfaces of silicon cells textured in various ways are characterised by an appropriate optical setup. The results are compared to those of conventional ray tracing. For surfaces with regular inverted pyramids, we identified reflected light diffraction patterns that can be explained by the principles of geometrical optics. These reflected light patterns can be used to extract details of surface morphologies and hence be used as a tool to fine tune and monitor fabrication processes. Surfaces with random pyramids reflect light without diffraction patterns but with other distinctive features. Their reflections lie primarily in the angular range between 0° and 50°, with a maximum intensity at about 25°. The impact of the encapsulant's refractive index on the amount of total internal reflection is discussed for various types of textured surface. For both random and regularly textured surfaces, it appears possible to achieve higher total internal reflection ratio when the encapsulant's index increases from conventional 1.5 to 1.6.

Use of photovoltage for electrodeposition in solar cell processing technology

Reports the development of a new technology for the electrolytic deposition of a metal on a solar cell, without employing an external electric bias field, but by using the internal photo-induced voltage of the solar cell itself. The experimental details of depositing silver over the existing metallised contact structure of the cell and a transparent conducting oxide coating over the entire solar cell front surface are discussed. The proposed technique reduces the consumption of the processing materials and makes the fabrication procedure less expensive and simpler.