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Ajay Upadhyaya

Bio: Ajay Upadhyaya 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 17, co-authored 76 publications receiving 913 citations.


Papers
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Journal ArticleDOI
TL;DR: In this paper, the use of ion-implantation for high-volume manufacturing of silicon solar cells is presented, which provides a unique opportunity to obtain grid-parity because it simplifies the fabrication of advanced cell structures.

108 citations

Journal ArticleDOI
TL;DR: In this article, a carrier-selective tunnel oxide passivated rear contact for high-efficiency screen-printed large area n-type front junction crystalline Si solar cells was proposed.
Abstract: This paper reports on the implementation of carrier-selective tunnel oxide passivated rear contact for high-efficiency screen-printed large area n-type front junction crystalline Si solar cells. It is shown that the tunnel oxide grown in nitric acid at room temperature (25°C) and capped with n+ polysilicon layer provides excellent rear contact passivation with implied open-circuit voltage iVoc of 714 mV and saturation current density J0b′ of 10.3 fA/cm2 for the back surface field region. The durability of this passivation scheme is also investigated for a back-end high temperature process. In combination with an ion-implanted Al2O3-passivated boron emitter and screen-printed front metal grids, this passivated rear contact enabled 21.2% efficient front junction Si solar cells on 239 cm2 commercial grade n-type Czochralski wafers. Copyright © 2016 John Wiley & Sons, Ltd.

83 citations

Journal ArticleDOI
TL;DR: In this paper, an effective chemical etching treatment to remove a boron-rich layer which has a significant negative impact on n-type silicon (Si) solar cells with a BORON emitter was reported.
Abstract: This paper reports on an effective chemical etching treatment to remove a boron-rich layer which has a significant negative impact on n-type silicon (Si) solar cells with boron emitter. A nitric acid-grown oxide/silicon nitride stack passivation on the boron-rich layer-etched boron emitter markedly decreases the emitter saturation current density J0e from 430 to 100 fA/cm2. This led to 1.6% increase in absolute cell efficiency including 22 mV increase in open-circuit voltage Voc and 1.9 mA/cm2 increase in short-circuit current density Jsc. This resulted in screen-printed large area (239 cm2) n-type Si solar cells with efficiency of 19.0%.

49 citations

Journal ArticleDOI
TL;DR: In this paper, the detailed optical properties of various SiN films and their effect on silicon solar cell efficiency in air and under glass is evaluated by a combination of Monte-Carlo geometrical ray tracing program, Sunrays, and a device modeling program PC1D.
Abstract: Plasma-enhanced chemical vapor deposition (PECVD) SiN films are widely used as antireflection (AR) coating for silicon solar cells and particularly for multi-crystalline solar cells for hydrogen passivation of bulk defects. In this paper, the detailed optical properties of various SiN films and their effect on silicon solar cell efficiency in air and under glass is evaluated by a combination of Monte-Carlo geometrical ray tracing program, Sunrays, and a device modeling program PC1D. Maximum module power under glass and ethylene vinyl acetate (EVA) encapsulation is used as the figure of merit for optimizing the index and thickness of the SiN films. Simulations are categorized by surface morphology (planar or textured) and ambient (air or glass). SiN films with refractive index (n) in the range of 2.03–2.42 are used for this study. It is found that although n = 2.03 is not the optimum index in terms of reflectance under glass (n = 1.5), it produces maximum cell or module efficiency under glass. This is because n = 2.03 film produces much higher cell efficiency (17.9%) in air, therefore, even after a significant optical encapsulation loss of 0.8% in absolute efficiency, the cell efficiency remains highest (17.1%) under glass. In contrast SiN film with an index of 2.4 produces only 0.5% air to glass efficiency loss but due to the low starting efficiency of 17% in air; the final cell efficiency under glass is only 16.5%. In addition, texturing provides a larger window of thickness around the optimum without affecting the optical performance. Similar analysis done for planar cells indicate that optimum index for highest module power is 2.20. This is because reflection is much higher in planar cells, therefore higher index can be tolerated before loss due to absorption in SiN exceeds the gain in reflectance under glass. Copyright © 2011 John Wiley & Sons, Ltd.

48 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


Cited by
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Journal ArticleDOI
TL;DR: In this article, the authors review the dynamic field of crystalline silicon photovoltaics from a device-engineering perspective and give an up-to-date summary of promising recent pathways for further efficiency improvements and cost reduction employing novel carrierselective passivating contact schemes, as well as tandem multi-junction architectures, in particular those that combine silicon absorbers with organic-inorganic perovskite materials.
Abstract: With a global market share of about 90%, crystalline silicon is by far the most important photovoltaic technology today. This article reviews the dynamic field of crystalline silicon photovoltaics from a device-engineering perspective. First, it discusses key factors responsible for the success of the classic dopant-diffused silicon homojunction solar cell. Next it analyzes two archetypal high-efficiency device architectures – the interdigitated back-contact silicon cell and the silicon heterojunction cell – both of which have demonstrated power conversion efficiencies greater than 25%. Last, it gives an up-to-date summary of promising recent pathways for further efficiency improvements and cost reduction employing novel carrier-selective passivating contact schemes, as well as tandem multi-junction architectures, in particular those that combine silicon absorbers with organic–inorganic perovskite materials.

751 citations

Journal ArticleDOI
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: In this article, the efficiency of n-type silicon solar cells with a front side boron-doped emitter and a full-area tunnel oxide passivating electron contact was studied experimentally as a function of wafer thickness W and resistivity ρ b.

470 citations