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Title: Solar cell efficiency and high temperature processing of n-type silicon grown by the noncontact crucible method

Journal Article · · Energy Procedia (Online)
 [1];  [2];  [1];  [3];  [4];  [4];  [4];  [1];  [2];  [1]
  1. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
  2. National Renewable Energy Lab. (NREL), Golden, CO (United States)
  3. FUTURE-PV Innovation, Fukushima (Japan)
  4. CEA, LITEN, INES, Le Bourget du Lac (France)
+ Show Author Affiliations

The capital expense (capex) of conventional crystal growth methods is a barrier to sustainable growth of the photovoltaic industry. It is challenging for innovative techniques to displace conventional growth methods due the low dislocation density and high lifetime required for high efficiency devices. One promising innovation in crystal growth is the noncontact crucible method (NOC-Si), which combines aspects of Czochralski (Cz) and conventional casting. This material has the potential to satisfy the dual requirements, with capex likely between that of Cz (high capex) and multicrystalline silicon (mc-Si, low capex). In this contribution, we observe a strong dependence of solar cell efficiency on ingot height, correlated with the evolution of swirl-like defects, for single crystalline n-type silicon grown by the NOC-Si method. We posit that these defects are similar to those observed in Cz, and we explore the response of NOC-Si to high temperature treatments including phosphorous diffusion gettering (PDG) and Tabula Rasa (TR). The highest lifetimes (2033 us for the top of the ingot and 342 us for the bottom of the ingot) are achieved for TR followed by a PDG process comprising a standard plateau and a low temperature anneal. Further improvements can be gained by tailoring the time-temperature profiles of each process. Lifetime analysis after the PDG process indicates the presence of a getterable impurity in the as-grown material, while analysis after TR points to the presence of oxide precipitates especially at the bottom of the ingot. Uniform lifetime degradation is observed after TR which we assign to a presently unknown defect. Lastly, future work includes additional TR processing to uncover the nature of this defect, microstructural characterization of suspected oxide precipitates, and optimization of the TR process to achieve the dual goals of high lifetime and spatial homogenization.

Research Organization:
National Renewable Energy Laboratory (NREL), Golden, CO (United States)
Sponsoring Organization:
USDOE Office of Energy Efficiency and Renewable Energy (EERE), Solar Energy Technologies Office (EE-4S), SunShot National Laboratory Multiyear Partnership (SuNLaMP); National Science Foundation (NSF)
Grant/Contract Number:
AC36-08GO28308
OSTI ID:
1348151
Report Number(s):
NREL/JA-5J00-68182
Journal Information:
Energy Procedia (Online), Vol. 92, Issue C; ISSN 1876-6102
Publisher:
ElsevierCopyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 10 works
Citation information provided by
Web of Science

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Sacrificial high-temperature phosphorus diffusion gettering process for lifetime improvement of multicrystalline silicon wafers
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Darwin at High Temperature: Advancing Solar Cell Material Design Using Defect Kinetics Simulations and Evolutionary Optimization journal May 2014

Cited By (1)

Processing Methods of Silicon to its Ingot: a Review journal September 2018

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Related Subjects

14 SOLAR ENERGY
36 MATERIALS SCIENCE
silicon
noncontact crucible
defect
swirl
lifetime
tabula rasa
gettering
capex