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Rohatgi, Ajeet

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Author: Ruby, D. S. × Start date: 1990 × search.filters.applied.f.isOrgUnitOfPublicationTitle: University Center of Excellence for Photovoltaics × Type: Text ×

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RIE-Texturing of Multicrystalline Silicon Solar Cells

2001-06 , Ruby, D. S. , Zaidi, S. H. , Narayanan, S. , Damiani, Benjamin Mark , Rohatgi, Ajeet

We developed a maskless plasma texturing technique for multicrystalline silicon (mc-Si) cells using Reactive Ion Etching (RIE) that results in higher cell performance than that of standard untextured cells. Elimination of plasma damage has been achieved while keeping front reflectance to extremely low levels. Internal quantum efficiencies as high as those on planar cells have been obtained, boosting cell currents and efficiencies by up to 7% on evaporated metal and 4% on screen-printed cells.

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Comparison of Front and Back Surface Passivation Schemes for Silicon Solar Cells

1998-07 , Moschner, J. D. , Doshi, P. , Ruby, D. S. , Lauinger, T. , Aberle, A. G. , Rohatgi, Ajeet

This work presents a comprehensive study on fast, low-cost methods for the electronic passivation of the phosphorus-diffused front surface and the non-diffused p-type rear surface of crystalline Si solar cells. Titanium dioxide is compared with rapidly-grown thermal oxide (RTO) and PECVD silicon nitrides from three different laboratories. Double layers of RTO and Ti02 or SiN are also investigated. We demonstrate that SiN and RTO single layers can provide very good passivation on both the front and back surface of solar cells. It is also shown that double layers consisting of a thin RTO film and silicon nitride can improve the passivation quality of most SiN layers, and enhance the stability under thermal treatment. With the proper choice of RTO, SiN, and thermal treatment, excellent surface recombination velocities on the back as well as very low emitter saturation currents can he reached using these fast, industrially feasible methods. All films used also provide or are compatible with a good antireflection coating of the cell surface.

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Rapid Thermal Technologies for High Efficiency Silicon Solar Cells

2001-06 , Ebong, Abasifreke , Cho, Y. H. , Hilali, Mohamed M. , Rohatgi, Ajeet , Ruby, D. S.

This paper shows that rapidly formed emitters (≤ 6 min) in a conveyor belt furnace or 3 minutes in an RTP system, in conjunction with a screen-printed (SP) RTP Al-BSF and passivating oxide formed simultaneously in 2 minutes can produce high efficiency cells with no surface texturing, point contacts, or selective emitter. It is shown for the first time that an 80 Ω/ emitter and SP Al-BSF formed in a high throughput belt furnace can produce 19% FZ cells, 18.4% MCZ cells and greater than 17% CZ cells with photolithography (PL) contacts. Using PL contacts, we also achieved 19% efficient cells on FZ, >18% on MCZ, and ~17% boron-doped CZ by emitter and SP Al-BSF formation in less than 10 minutes in a single wafer RTP system. Finally, a manufacturable process with 45 Ω/ emitter and screen-printed (SP) Al-BSF and Ag contacts formed in the conveyor belt furnace gave 17% efficient cells on FZ silicon. Compared to the photolithography cells, the SP cell gave ∼2% lower efficiency along with a decrease in Jsc and fill factor (FF). This loss in performance is attributed to a combination of the poor blue response, higher series resistance and higher contact shading in the SP devices.

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Effective Passivation of the Low Resistivity Silicon Surface by a Rapid Thermal Oxide/PECVD Silicon Nitride Stack and Its Application to Passivated Rear and Bifacial Si Solar Cells

1998-07 , Rohatgi, Ajeet , Narasimha, S. , Ruby, D. S.

A novel stack passivation scheme, in which plasma silicon nitride (SiN) is stacked on top of a rapid thermal SiO(2) (RTO) layer, is developed to attain a surface recombination velocity (S) approaching 10 em/s at the 1.3 Ω-cm p-type (l00) silicon surface. Such low S is achieved by the stack even when the RTO and SiN films individually yield considerably poorer surface passivation. Critical to achieving low S by the stack is the use of a short, moderae temperature anneal (in this study 730°C for 30 seconds) after film growth and deposition. This anneal is believed to enhance the release and delivery of atomic hydrogen from the SiN film to the Si-Si0(2) interface, thereby reducing the density of interface traps at the surface. Compatibility with this post-deposition anneal makes the stack passivation scheme attractive for cost-effective solar cell production since a similar anneal is required to fire screen-printed contacts. Application of the stack to passivated rear screen-printed solar cells has resulted in V(oc)'s of 641 mV and 633 mV on 0.65 Ω-cm and 1.3 Ω-cm FZ Si substrates, respectively. These V(oc) values are roughly 20 mV higher than for cells with untreated, highly recombinative back surfaces. The stack passivation has also been used to form fully screen-printed bifacial solar cells which exhibit rear-illuminated efficiency as high as 11.6% with a single layer AR coating.

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Development of RIE-Textured Silicon Solar Cells

2000-09 , Damiani, Benjamin Mark , Ludemann, R. , Ruby, D. S. , Zaidi, S. H. , Rohatgi, Ajeet

A maskless plasma texturing technique using Reactive Ion Etching for silicon solar cells results in a very low reflectance of 5.4 % before and 3.9 % after SiN deposition. A detailed study of surface recombination and emitter properties was made, then solar cells were fabricated using the DOSS solar cell process. Different plasma damage removal treatments are tested to optimize low lifetime solar cell efficiencies. Highest efficiencies are observed for little or no plasma-damage removal etching on mc-Si. Increased & due to the RIE texture proved superior to a single layer anti-reflection coating. This indicates that RIE texturing is a promising texturing technique, especially applicable on lower lifetime (multicrystalline) silicon. The use of non-toxic, non-corrosive SFS makes this process attractive for mass production.

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