Papers by Keyword: Light Trapping

Abstract: Thin crystalline silicon (c-Si) suffers from poor light absorption which hinders generation of high photocurrent in photovoltaic (PV) devices. To overcome this issue, efficient light trapping (LT) schemes need to be incorporated into the thin c-Si absorber. This paper presents ray tracing of LT schemes in thin c-Si to enhance broadband light absorption within 300-1200 nm wavelength region. For the ray tracing, mono c-Si wafer with 100 μm thickness is investigated and solar spectrum (AM1.5G) at normal incidence is used. Front and rear pyramid textures, silicon nitride (SiN_x) anti-reflective coating (ARC) and back surface reflector (BSR) are the LT schemes being studied in this work. With incremental LT schemes, optical properties of the thin c-Si are analyzed. From the absorption curve, maximum potential photocurrent density (J_max) is calculated, assuming unity carrier collection. The c-Si reference (without LT) exhibits J_max of 24.93 mA/cm². With incorporation of incremental LT schemes into the thin c-Si, the J_max increases, owing to enhanced light coupling and light scattering in the c-Si absorber. The J_max up to 42.12 mA/cm² is achieved when all the LT schemes are incorporated into the thin c-Si absorber. This represents 69% enhancement when compared to the J_max of the c-Si reference.

Abstract: The optical properties have been numerically investigated in crystalline silicon nanoholes array for various structural parameters. We have demonstrated that the light absorption can be greatly enhanced in silicon nanoholes array especially for long wavelength absorption compared with single diameter nanoholes array. We have also obtained the optimal parameters for absorption wavelength control, at which the photocurrent enhancement factors have been achieved to be 14.43% compared to silicon thin film. Furthermore, the underlying mechanism of the absorption enhancement in dual-diameter nanoholes array has been discussed.

Abstract: Tandem Solar Cells with Silicon as one of its constituents have flat surfaces (surfaces without texturing). That is why flat surfaces Solar cells have got quite importance. But the issue with the flat surfaces is the high reflection loss (flat) and poor light trapping (no-texturing) in the cells. So, some scattering film, other than direct texturing, that is polydimethylsiloxane (PDMS) polymer with the texture is used. The optimized PDMS film here is the random pyramidal film because random pyramidal PDMS films have a drop of 56.6% in reflectance used on polished Silicon while iso-textured and inverted pyramids have 51.55% and 48.47% respectively. This PDMS film with random textures when applied to 2-terminal monolithic perovskite/Silicon tandem, its external quantum efficiency shows an increase of 1.12mA/cm² in the short-circuit current and reflection loss reduces by 4.1 mA/cm².

Abstract: To reduce the cost of solar electricity, there is an enormous potential of thin-film photovoltaic technologies. An approach for lowering the manufacturing costs of solar cells is to use organic (polymer) materials that can be processed under less demanding conditions. Organic/polymer solar cells have many intrinsic advantages, such as their light weight, flexibility, and low material and manufacturing costs. But reduced thickness comes at the expense of performance. However, thin photoactive layers are widely used, but light-trapping strategies, due to the embedding of plasmonic metallic nanoparticles have been shown to be beneficial for a better optical absorption in polymer solar cells. This article reviews the different plasmonic effects occurring due to the incorporation of metallic nanoparticles in the polymer solar cell. It is shown that a careful choice of size, concentration and location of plasmonic metallic nanoparticles in the device result in an enhancement of the power conversion efficiencies, when compared to standard organic solar cell devices.Contents of Paper

Abstract: Optical losses chiefly effect the power from a solar cell by lowering the short-circuit current. There are a number of ways to reduce the optical losses, which includes top contact coverage of the cell surface can be minimized, anti-reflection coatings can be used on the top surface of the cell, reflection can be reduced by surface texturing, and the optical path length in the solar cell may be increased by a combination of surface texturing and light trapping. This work discusses all of the methods to reduce optical losses of silicon solar cells. Surface texturing, either in combination with an anti-reflection coating or by itself, can be used to minimize reflection, but the large reflection loss can be reduced significantly via a suitable anti-reflecting coatings. Significant improvement of the short circuit current after light trapping design was observed. In addition to these methods, top contact design of silicon solar cells is important. The design of the top contact involves the minimization of the finger and busbar resistance, and the overall reduction of losses associated with the top contact.

Abstract: The reflectance of the hexagonal array silicon nanohole structure was systematically studied using various measurements and through simulations. It was found that the hexagonal array silicon nanohole can reduce the reflectance along the entire spectrum range by approximately 6%. It is suggested that the enhancement of the electric field intensity at short wavelength is mainly due to the large surface area provided by the nanohole structure, while multiple reflections occurring in the nanohole contribute to electric field enhancement in the long wavelength range. In addition, the simulation of a hexagonal array silicon nanohole coated with a thin layer of indium tin oxide (ITO) was carried out. The results show that reflectance is greatly decreased along nearly the entire spectrum range, except from 400 nm to 440 nm, and almost zero reflectance is achieved at wavelengths from 650 nm to 750 nm. The results provide a practical guideline to the design and fabrication of a low-reflectance, and as a consequence, a high-efficiency hexagonal array silicon nanohole solar cell.

Abstract: We show that the optical absorption in thin-film photovoltaic cells can be enhanced by texturing the silicon absorbing layer into nanostructured array. The optical absorption of the proposed configuration is enhanced by 70% compared to a nonpatterned silicon thin film of the same thickness. Furthermore, the proposed silicon thin film PV cell has a good angle-independent response of up to 60°. The omnidirectional absorbance enhancement of the nanopatterned silicon thin film is attributed to its unusual light trapping mechanism and omnidirectional bandgap.

Abstract: ZnO:Al thin films were deposited on low-iron glass substrates (size: 1100×1400 mm2 ) in an in-line sputtering system, using ZnO:Al ceramic targets. The initially smooth films exhibit high transparencies (T≥85% for visible light) and excellent electrical properties (carrier concentration N=3.810×1020cm-3, mobility μ=20.47 cm2/V•s). The films, etched by diluted HCl for different time, appear roughness morphology with suitable angles and crater structure, used for controlling the light scattering properties of the textured ZnO:Al films. Moreover, the electrical properties are not affected by the etching process. Thus, it is possible to optimize separately the electro-optical and light trapping properties. The textured ZnO:Al films (haze 21.2%, 550 nm) were used as front contacts for amorphous silicon thin film solar cells prepared by PECVD, 6.5% conversion efficiency were obtained.

Abstract: Back–side diffraction gratings enhance a solar cell’s near–band–gap response by diffracting light into higher orders and thereby reducing front–side escape losses. The resulting increased photon absorption and carrier generation improves short–circuit current densities and solar cell efficiencies. Combining rigorous coupled–wave analysis and ray tracing yields a three–dimensional, polarization sensitive optical model to calculate Si absorbance, front–side and back–side losses. For industrially used, pyramidally textured, 180 μm Si solar cells with 85 nm SiN_x anti–reflection coating, the application of an optimized back–side grating enhances the short–circuit current density by ≈ +1 mA/cm², a relative increase of ≈ +2.7 %.

Abstract: Light trapping in the absorber layer of thin-film solar cells is of great importance for obtaining a high photocurrent. A novel light-trapping technique is based on light scattering by metal nanoparticles through excitation of localized surface plasmons. By evaporation of thin silver layers of different thicknesses followed by thermal annealing, silver nanoparticles with different sizes were formed. We show that the plasmon resonance wavelength can be tuned by changing the embedding medium and the particle size. Furthermore, amorphous silicon solar cells with silver nanoparticles embedded between the absorber layer and the back reflector were fabricated. The effect of different sizes of the particles on the solar cell performance was studied. The performance of the solar cells was characterized by quantum efficiency and current-voltage measurements. Both the external quantum efficiency in the wavelength region of 600 to 800 nm and the current density increase as particle size increases, but remain lower than those of the reference device without particles. These results demonstrate that nanoparticles can enhance light trapping, provided that parasitic absorption in the nanoparticles is minimized. This can be achieved by better control of particle shape and size using improved fabrication techniques.