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Arnab Das

Bio: Arnab Das is an academic researcher from Georgia Institute of Technology. The author has contributed to research in topics: Passivation & Silicon. The author has an hindex of 11, co-authored 25 publications receiving 449 citations.

Papers
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Journal ArticleDOI
TL;DR: In this article, a hierarchical structure was developed for a two-tier texturing method for lower light reflection using an antireflection coating (ARC) to reduce light reflectance via destructive interference of the reflected light at the air-ARC-substrate interfaces.
Abstract: Low conversion efficiency is still the main limiting factor for current solar-cell technologies. A large portion of the energy loss during solar-cell operation is attributed to optical loss, namely the loss of the incoming light by reflection.[1] To reduce the reflection loss, surface texturing and antireflection coatings are the most-commonly used strategies.[2–4] Surface texturing is able to enhance light trapping by multiplying the internal reflections. The industrial standard for the current Si-based photovoltaic (PV) industry process is alkaline fabrication of micrometer-sized pyramid textures. An emerging focus today is the incorporation of nanostructures as surface-texturing materials.[5–8] For example, porous Si and Si nanowires (NWs) have been applied to solar cells to effectively reduce the reflection loss.[9–11] Xiu et al. developed a hierarchical structure through a two-tier texturing method for lower light reflection.[12] Using an antireflection coating (ARC) is another method to reduce light reflectance via destructive interference of the reflected light at the air–ARC–substrate interfaces. A single-layer ARC, such as silicon nitride (SiNx), is the industry standard ARC on Si PVs.[13] A further reduction of reflection can be achieved through a multilayer ARC or fine control of the ARC geometry, which enables a gradual transition of the refraction index from air to the silicon.[14,15] As an outstanding 1D nanostructure, ZnO NWs have a high transparency due to the wide bandgap, appropriate refractive index (n ≈ 2 at 600 nm), and the capability of forming a textured coating on virtually any substrate.[16–19] These characteristics make it an attractive dielectric ARC material for PV applications. By the integration of ZnO NWs with optical fibers and quartz waveguides, an enhancement of the efficiency by a factor of 4–6 has been shown by utilizing a three-dimensional approach.[20,21] The application of ZnO nanostructures on planar Si as an ARC for solar cells has achieved a weighted reflectance

93 citations

Journal ArticleDOI
TL;DR: Hierarchically textured Si is explored for low reflection, and self-cleaning solar cells, which was fabricated from micropyramids with nanostructures that were added by Au-assisted electroless chemical etching as mentioned in this paper.

66 citations

Journal ArticleDOI
TL;DR: In this article, a combination of optimized front and back dielectrics, rear surface finish, oxide thickness, fixed oxide charge, and interface quality provided effective surface passivation without parasitic shunting.
Abstract: This paper describes the cell design and technology on large-area (239 cm2) commercial grade Czochralski Si wafers using industrially feasible oxide/nitride rear passivation and screen-printed local back contacts. A combination of optimized front and back dielectrics, rear surface finish, oxide thickness, fixed oxide charge, and interface quality provided effective surface passivation without parasitic shunting. Increasing the rear oxide thickness from 40 to 90 A in conjunction with reducing the surface roughness from 1.3 to 0.2 μm increased the Voc from 640 mV to 656 mV. Compared with 18.6% full aluminum back surface field (Al-BSF) reference cell, local back-surface field (LBSF) improved the back surface reflectance (BSR) from 65% to 93% and lowered the back surface recombination velocity (BSRV) from 310 to 130 cm/s. Two-dimensional computer simulations were performed to optimize the size, shape, and spacing of LBSF regions to obtain good fill factor (FF). Model calculations show that 20% efficiency cells can be achieved with further optimization of local Al-BSF cell structure and improved screen-printed contacts.

45 citations

Journal ArticleDOI
TL;DR: In this paper, a boron diffusion process using boric acid as a low cost, nontoxic spin-on source is introduced, achieving sheet resistances ranging from 20 to 200 Ω/□ with saturation current densities as low as 85 fA/cm 2.
Abstract: A boron diffusion process using boric acid as a low cost, nontoxic spin-on source is introduced. Using dilute solutions of boric acid, sheet resistances ranging from 20 to 200 Ω/□ were achieved, along with saturation current densities as low as 85 fA/cm 2 . These results indicate that boric acid is a suitable source for forming both p + emitters and back surface fields for high efficiency n- and p-type solar cells. The degradation of the minority carrier bulk lifetime, which is a common efficiency-limiting characteristic of low cost boron sources, was also minimized through the use of a high purity boric acid source. The ability to achieve low sheet resistances, high bulk lifetimes and low saturation current densities with boric acid were exploited to achieve a 19.7% efficient screen printed solar cell exhibiting a bulk lifetime >400 μs.

36 citations

Journal ArticleDOI
TL;DR: In this article, a thin thermal-SiO2/SiNX stack was demonstrated to provide similar passivation on both p+ and n+ surfaces, and a spin-on boric acid source was used to create uniform, well-passivated p+ emitters on textured surfaces.
Abstract: N-type Si cells offer a compelling alternative to p-type cells to achieve high, stabilized cell efficiencies because they do not suffer from light-induced degradation. However, the most common dielectric materials that are used to passivate the n+ emitters of p-type cells-thermal SiO2 and SiNX-have historically provided poor passivation of the p+ emitters required for n-type cells. In this paper, we demonstrate that a thin thermal-SiO2/SiNX stack can, when appropriately fired, provide similar passivation on both p+ and n+ surfaces. Passivation studies on textured, SiO2/SiNX passivated p+-Si surfaces indicate that a high-temperature firing cycle is the most important step to achieving high-quality passivation and that the positive charge in the dielectric stack may have little detrimental effect on industrial-type, high surface concentration emitters. In addition, the suitability of spin-on boric acid sources for forming uniform, well-passivated p+ emitters on textured surfaces was studied. This passivation scheme and spin-on boron source were used to achieve 4-cm2 screen-printed n-type cells with efficiencies over 20% and open-circuit voltages up to 650 mV.

31 citations


Cited by
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TL;DR: In this paper, aluminum oxide (Al2O3) nanolayers synthesized by atomic layer deposition (ALD) have been used for the passivation of p-and n-type crystalline Si (c-Si) surfaces.
Abstract: The reduction in electronic recombination losses by the passivation of silicon surfaces is a critical enabler for high-efficiency solar cells. In 2006, aluminum oxide (Al2O3) nanolayers synthesized by atomic layer deposition (ALD) emerged as a novel solution for the passivation of p- and n-type crystalline Si (c-Si) surfaces. Today, high efficiencies have been realized by the implementation of ultrathin Al2O3 films in laboratory-type and industrial solar cells. This article reviews and summarizes recent work concerning Al2O3 thin films in the context of Si photovoltaics. Topics range from fundamental aspects related to material, interface, and passivation properties to synthesis methods and the implementation of the films in solar cells. Al2O3 uniquely features a combination of field-effect passivation by negative fixed charges, a low interface defect density, an adequate stability during processing, and the ability to use ultrathin films down to a few nanometers in thickness. Although various methods can be used to synthesize Al2O3, this review focuses on ALD—a new technology in the field of c-Si photovoltaics. The authors discuss how the unique features of ALD can be exploited for interface engineering and tailoring the properties of nanolayer surface passivation schemes while also addressing its compatibility with high-throughput manufacturing. The recent progress achieved in the field of surface passivation allows for higher efficiencies of industrial solar cells, which is critical for realizing lower-cost solar electricity in the near future.

684 citations

Journal ArticleDOI
TL;DR: With worldwide efforts, innovations in chemistry and materials elaborated in this review will push forward the frontiers of smart textiles, which will soon revolutionize the authors' lives in the era of Internet of Things.
Abstract: Textiles have been concomitant of human civilization for thousands of years. With the advances in chemistry and materials, integrating textiles with energy harvesters will provide a sustainable, environmentally friendly, pervasive, and wearable energy solution for distributed on-body electronics in the era of Internet of Things. This article comprehensively and thoughtfully reviews research activities regarding the utilization of smart textiles for harvesting energy from renewable energy sources on the human body and its surroundings. Specifically, we start with a brief introduction to contextualize the significance of smart textiles in light of the emerging energy crisis, environmental pollution, and public health. Next, we systematically review smart textiles according to their abilities to harvest biomechanical energy, body heat energy, biochemical energy, solar energy as well as hybrid forms of energy. Finally, we provide a critical analysis of smart textiles and insights into remaining challenges and future directions. With worldwide efforts, innovations in chemistry and materials elaborated in this review will push forward the frontiers of smart textiles, which will soon revolutionize our lives in the era of Internet of Things.

536 citations

Journal ArticleDOI
TL;DR: In this article, a review gives an overview of recent advances in the potential applications of superhydrophobic materials, which are characterized by extremely high water contact angles and various adhesion properties.
Abstract: This review gives an overview of recent advances in the potential applications of superhydrophobic materials. Such properties are characterized by extremely high water contact angles and various adhesion properties. The conception of superhydrophobic materials has been possible by studying and mimicking natural surfaces. Now, various applications have emerged such as anti-icing, anti-corrosion and anti-bacterial coatings, microfluidic devices, textiles, oil–water separation, water desalination/purification, optical devices, sensors, batteries and catalysts. At least two parameters were found to be very important for many applications: the presence of air on superhydrophobic materials with self-cleaning properties (Cassie–Baxter state) and the robustness of the superhydrophobic properties (stability of the Cassie–Baxter state). This review will allow researchers to envisage new ideas and industrialists to advance in the commercialization of these materials.

470 citations

Journal ArticleDOI
TL;DR: In this article, the use of black silicon (BSi) as an anti-reflection coating in solar cells is examined and appraised, based upon strategies towards higher efficiency renewable solar energy modules.
Abstract: Black silicon (BSi) represents a very active research area in renewable energy materials. The rise of BSi as a focus of study for its fundamental properties and potentially lucrative practical applications is shown by several recent results ranging from solar cells and light-emitting devices to antibacterial coatings and gas-sensors. In this paper, the common BSi fabrication techniques are first reviewed, including electrochemical HF etching, stain etching, metal-assisted chemical etching, reactive ion etching, laser irradiation and the molten salt Fray-Farthing-Chen-Cambridge (FFC-Cambridge) process. The utilization of BSi as an anti-reflection coating in solar cells is then critically examined and appraised, based upon strategies towards higher efficiency renewable solar energy modules. Methods of incorporating BSi in advanced solar cell architectures and the production of ultra-thin and flexible BSi wafers are also surveyed. Particular attention is given to routes leading to passivated BSi surfaces, which are essential for improving the electrical properties of any devices incorporating BSi, with a special focus on atomic layer deposition of Al2O3. Finally, three potential research directions worth exploring for practical solar cell applications are highlighted, namely, encapsulation effects, the development of micro-nano dual-scale BSi, and the incorporation of BSi into thin solar cells. It is intended that this paper will serve as a useful introduction to this novel material and its properties, and provide a general overview of recent progress in research currently being undertaken for renewable energy applications.

397 citations

Journal ArticleDOI
TL;DR: Inspired by the structures of the insect compound eyes, nanostructure arrays (NSAs) have been developed as effective antireflective surfaces, which exhibit promising broadband and quasi-omnidirectional properties together with multifunctions.
Abstract: Reducing the reflection and improving the transmission or absorption of light from wide angles of incidence in a broad wavelength range are crucial for enhancing the performance of the optical, optoelectronic, and electro-optical devices. Inspired by the structures of the insect compound eyes, nanostructure arrays (NSAs) have been developed as effective antireflective surfaces, which exhibit promising broadband and quasi-omnidirectional antireflective properties together with multifunctions. This review summarizes the recent advances in the fabrication and performance of antireflective surfaces based on NSAs of a wide variety of materials including silicon and non-silicon materials. The applications of the NSA-based antireflective surfaces in solar cells, light emitting diodes, detection, and imaging are highlighted. The remaining challenges along with future trends in NSA-based antireflective surfaces are also discussed.

312 citations