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He J.,Peking University | Mao Q.,Optony Inc. | Zhang X.,Optony Inc. | Zhang S.,Peking University | And 4 more authors.
Energy Education Science and Technology Part A: Energy Science and Research | Year: 2014

In the conventional "precursor-selenization" process for Cu(InGa)Se2 (CIGS) thin films, Ga accumulates near the Mo back contact when the selenization is carried out at a relatively low temperature (550°C). This results in a low open-circuit voltage. If the selenization occurs at a higher temperature, i.e. 700°C, the crystallinity of the film is poor which results in a low fill factor. To obtain both high open-circuit voltage and high fill factor films, a two-step selenization process using Se pellets was examined: the precursors were firstly selenized at 550°C for 20 minutes, and then sequentially selenized for 10 minutes after temperature ramped up to 700°C. This process produces CIGS absorber films with high crystallinity as well as high band-gap, and the solar cell efficiency increases from 9.71% to 11.11% compared with conventional process. © Sila Science. All rights reserved.

Tian L.,Peking University | Zhang X.-Y.,Optony Inc. | Mao Q.-N.,Optony Inc. | Li X.-G.,Optony Inc. | And 2 more authors.
Wuji Cailiao Xuebao/Journal of Inorganic Materials | Year: 2015

CIGS absorber layers were prepared by sequential sputtering/selenization method. Based on that, CIGS solar cells were fabricated with a structure of glass/Mo/CIGS/CdS/i-ZnO/ZnO:Al/Ni-Al grid. The influences of annealing treatment on the performance of CIGS solar cells were investigated. By optimizing annealing condition, the cell efficiency increased from 4.91% to 14.01%. Further investigation revealed that the post-annealing treatment had two advantages. Firstly, it facilitated the diffusion of Cd ions into CIGS surface to substitute the Cu vacancies. Thus, the surface of CIGS converted from p-type to n-type conduction, leading to the shift of p-n junction from CIGS/CdS interface into the CIGS layer. Therefore, the recombination centers at the p-n junction were greatly reduced. Secondly, most H2O molecules being adsorbed on the CIGS surface were eliminated by annealing, which improved the uniformity of electrical properties and band-gap of CIGS layer, resulting better performance of CIGS solar cell. ©, 2015, Science Press. All right reserved.

Mao Q.-N.,Peking University | Zhang X.-Y.,Optony Inc. | Li X.-G.,Optony Inc. | He J.-X.,Peking University | And 2 more authors.
Wuli Xuebao/Acta Physica Sinica | Year: 2014

In the sequential sputtering/selenization process, Ga segregation at the back of Cu(In, Ga)Se2 (CIGS) absorber is frequently observed. In this paper, Ga diffusion in CIGS absorber is investigated during the sputtering and selenization process. Results show that Ga diffusion is closely related to Cu/(In+Ga) ratio in the metallic precursors and the selenization temperature, but barely influenced by Ga/(In+Ga) ratio in the metallic precursors. Based on Fick's second law, a simplified model is established to describe Ga diffusion from the back to the surface of CIGS absorber, which suggests that Ga diffusion coefficient is the dominant factor to constrain Ga content near the absorber surface. By process optimization, Ga/(In+Ga) ratio near the absorber surface is successfully increased. Accordingly, a CIGS solar cell device with efficiency of 12.42% has been obtained. © 2014 Chinese Physical Society.

Wang Q.,National Renewable Energy Laboratory | Page M.R.,National Renewable Energy Laboratory | Iwaniczko E.,National Renewable Energy Laboratory | Xu Y.-Q.,National Renewable Energy Laboratory | And 8 more authors.
Conference Record of the IEEE Photovoltaic Specialists Conference | Year: 2010

We study amorphous/crystalline silicon heterojunctions (Si HJ) in both p-type and n-type c-Si solar cells under high level of photon injection using concentrated light up to 55 suns. The performance of the cells under intensive light is similar to other types of crystalline Si solar cells. The open circuit voltage (Voc) increases logarithmically with light intensity for both n-type and p-type base cells and best 760 mV at 48 suns. The best cell efficiency peaks around 10 suns at 19.6% on an untextured p-type Si HJ cell. It represents an 11% increase of the efficiency relative to the one at 1 sun. The decrease of cell efficiency at a higher light intensity is mainly due to the decrease of fill factor (FF). We also found that the FF decreases much quickly in the cell with an n-type wafer compared to a p-type wafer. After more experiments with controlled front finger space, wafer bulk resistivity, and the area of the cells, we conclude that there is a difference in carrier collection for the heterojunction emitters of the n-type and of the p-type c-Si solar cells under intensive illumination. © 2010 IEEE.

News Article | August 29, 2008

The idea behind Optony, a year-old startup that is working on combining thin film solar cells with a solar concentrating system, is to merge two of the solar industry’s low-cost options to produce solar power prices that rival grid parity. At least that’s the theory — the company is still in the development phase. P. R. Yu, CEO and founder of the Sunnyvale, Calif.-based startup, tells us that the company has just started to raise a Series A round to help continue work on its rooftop and ground-mounted solar system. Usually, solar concentrating systems use mirrors and lenses to focus sun rays onto tiny, highly-efficient, multi-junction solar cells that can withstand the high concentrations and heat. The problem is that while only a small amount of the solar cell is used in these systems, the material itself can be pretty expensive. Yu says the company’s thin-film material, which it plans to manufacture itself, is cheaper than these cells as well as traditional silicon-based photovoltaics. But to stand up to concentrations and heat, the thin-film solar cells would have to be tweaked significantly. Yu wouldn’t discuss what the thin-film material was made of or how it was modified, only that it is to be able to withstand high heat. Thin-film material deposited onto glass could help with a modest dissipation of heat. Yu also wouldn’t describe the level of concentration, but we’re thinking it’s probably at a lower concentration than the high-powered systems being developed in other concentrating set-ups. Yu plans to first focus on the commercial market to sell the systems, and estimates the power output of the system between tens of kilowatts and a megawatt. So far, Yu says Optony has raised only angel funding and $250,000 from the Department of Energy’s Technology Commercialization Development Fund (TCDF). The company is also working to develop the technology with the National Renewable Energy Labs (where Yu worked for five years, previously). The merger of the low-cost solar options could be a winning idea, but we’ll wait to learn (and see) more from the firm before we get too excited.

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