PVI Paper

Cz-Si wafers in solar cell production: Efficiency-limiting defects and material quality control

Share on facebook
Facebook
Share on twitter
Twitter
Share on linkedin
LinkedIn
Share on reddit
Reddit
Share on email
Email

By Jonas Haunschild, luminescence Imaging Team Leader, Fraunhofer ISE; Juliane Broisch, In-line Measurement Techniques and Quality Assurance Group, Fraunhofer ISE; Isolde Reis, Member of the luminescence Imaging Team, Fraunhofer ISE; Stefan Rein, Head of the In-line Measurement Techniques and Quality Assurance Group, Fraunhofer ISE

Most high-efficiency solar cells are fabricated from monocrystalline Czochralski silicon (Cz-Si) wafers because the material quality is higher than multicrystalline silicon (mc-Si) wafers. However, the material study presented in this paper reveals strong variations in the material quality of commercially available Cz-Si wafers, leading to a loss in solar cell efficiency of 4% absolute. The reason for this is the presence of defects, which appear as dark rings in photoluminescence (PL) images of the finished solar cells. It is shown that these efficiency-limiting defects originate from oxygen precipitation during emitter diffusion. It is demonstrated that an incoming inspection in the as-cut state is difficult, as strong ring structures in as-cut wafers turn out to originate most often from thermal donors. These are dissolved during high-temperature treatments and are therefore harmless, whereas moderate ring structures in the as-cut state may become severe. That is why critical wafers can be identified and sorted out reliably only after emitter diffusion, by using QSSPC-based lifetime measurements or PL imaging. The two-year statistics gathered from the research line at Fraunhofer ISE on the occurrence of ring defects in Cz-Si wafers indicate that ring defects are highly relevant in terms of material yield.

L3dwLWNvbnRlbnQvdXBsb2Fkcy9sZWdhY3ktcHVibGljYXRpb24tcGRmcy9lZTdlYzU2NzZjLWN6c2ktd2FmZXJzLWluLXNvbGFyLWNlbGwtcHJvZHVjdGlvbi1lZmZpY2llbmN5bGltaXRpbmctZGVmZWN0cy1hbmQtbWF0ZXJpYWwtcXVhbGl0eS1jb250cm9sLnBkZg==

Published In

PVI Issue
The 15th edition of Photovoltaics International hopes to bring some optimism to 2012 by tackling the key factors on how to cope with the current situation. Contributions come from MIT on using TCAD as a viable method for modelling metal impurity evolution; Alternative Energy Investing presents a comprehensive look at materials cost; and efficiency improvements are on offer by ECN. REC Solar and Tata BP Solar report on module lifetime and IMS Research gives us a brief rundown of 2012 global market expectations.

Read Next

PVI Paper
Cell Processing, Photovoltaics International Papers
This paper presents preliminary results of SERIS’ biPolyTM cell: the bifacial application of polysiliconbased passivating contact stacks with front and rear screen-printed and fired metallization.
PVI Paper
Cell Processing, Photovoltaics International Papers
This work reports the latest results obtained at Jolywood for full-area (251.99cm2) n-type bifacial passivating-contact solar cells using a cost-effective process with industrially-feasible boron diffusion, phosphorus ion implantation and low-pressure chemical vapour deposition (LPCVD) with in situ oxidation.
PVI Paper
Cell Processing, Photovoltaics International Papers
This paper reviews the key technology improvements which have enabled a continuous 0.5%abs/year increase in efficiency of industrial PERC and PERC+ cells.
PVI Paper
Photovoltaics International Papers, Thin Film
This paper provides a concise overview of existing c-Si-based 2-, 3- and 4-terminal tandem technologies, summarizes the current development status, and sets out the future roadmap. In addition, a discussion is included of what will be required over the coming years to bring these promising technologies to market, enabling commercial efficiencies above 30%.
PVI Paper
Photovoltaics International Papers, Thin Film
This paper discusses, at both the cell and the module level, the balance between the advantages and drawbacks of increasing the cell bifaciality from a typical value of 90% towards 100%, or decreasing it towards that of monofacial cells (0%).
PVI Paper
Photovoltaics International Papers, PV Modules
Because it leads to higher efficiencies than aluminium back-surface field (Al-BSF) cells, passivated emitter and rear cell (PERC) technology is attracting more and more attention in the industry and gaining market share. However, PERC technology brings new challenges with regard to the phenomenon of degradation: some monofacial/bifacial PERC cell modules were found to demonstrate much higher power degradation than Al-BSF cell modules after damp-heat (DH: 85°C and 85% relative humidity RH, 1000h) and potential-induced degradation (PID: 85°C and 85% RH, –1,500V, 96h) tests, which will be the focus of this paper.

Subscribe to Newsletter

Upcoming Events

Solar Media Events, Upcoming Webinars
March 9, 2021
Solar Media Events
March 17, 2021
Solar Media Events
April 13, 2021
Solar Media Events
April 20, 2021
Solar Media Events
May 11, 2021