TY - JOUR

T1 - Impurity Gettering in Polycrystalline-Silicon Based Passivating Contacts

T2 - The Role of Oxide Stoichiometry and Pinholes

AU - Yang, Zhongshu

AU - Krügener, Jan

AU - Feldmann, Frank

AU - Polzin, Jana Isabelle

AU - Steinhauser, Bernd

AU - Le, Tien T.

AU - Macdonald, Daniel

AU - Liu, An Yao

N1 - Funding Information: This work was supported by the Australian Renewable Energy Agency (ARENA) through project 2017‐RND017 and the Australian Centre for Advanced Photovoltaics (ACAP). A.L. acknowledges funding from the ACAP Postdoctoral Fellowship scheme. This work has been made possible through the access to the ACT node of the Australian National Fabrication Facility (ANFF‐ACT) and the Australian Microscopy and Microanalysis Research Facility at the Centre for Advanced Microscopy, at the Australian National University (ANU). The authors are grateful to our ANU colleagues Dr. Felipe Kremer, Dr. Frank Brink, Dr. Li Li, and Dr. Thomas Ratcliff for assistance with the TEM, FIB, and ion implantation processes. The authors also thank Dr. Sieu Pheng Phang for his contribution to Quokka 3 simulation.

PY - 2022/6/23

Y1 - 2022/6/23

N2 - Polycrystalline-silicon/oxide (poly-Si/SiOx) passivating contacts for high efficiency solar cells exhibit excellent surface passivation, carrier selectivity, and impurity gettering effects. However, the ultrathin SiOx interlayer can act as a diffusion barrier for metal impurities and this potentially slows down the overall gettering rate of the poly-Si/SiOx structures. Herein, the factors that determine the blocking effects of the SiOx interlayers are identified and investigated by examining two general types of the SiOx interlayers: 1.3 nm ultrathin tunneling SiOx with negligible pinholes and 2.5 nm SiOx with thermally created pinholes. Iron is used as tracer impurity in silicon to quantify the gettering rate. By fitting the experimental gettering kinetics by a diffusion-limited segregation gettering model, the blocking effects of the SiOx interlayers are quantified by a transport parameter. Both the oxide stoichiometry and pinhole density affect the effective transport of iron through SiOx interlayers. The oxide stoichiometry depends strongly on the oxidation method, while the pinhole density is affected by the activation temperature, doping concentration, doping technique, and possibly the dopant type as well. To enable a fast gettering process during typical high-temperature formation of the poly-Si/SiOx structures, a SiOx interlayer that is less stoichiometric or with a higher pinhole density is preferred.

AB - Polycrystalline-silicon/oxide (poly-Si/SiOx) passivating contacts for high efficiency solar cells exhibit excellent surface passivation, carrier selectivity, and impurity gettering effects. However, the ultrathin SiOx interlayer can act as a diffusion barrier for metal impurities and this potentially slows down the overall gettering rate of the poly-Si/SiOx structures. Herein, the factors that determine the blocking effects of the SiOx interlayers are identified and investigated by examining two general types of the SiOx interlayers: 1.3 nm ultrathin tunneling SiOx with negligible pinholes and 2.5 nm SiOx with thermally created pinholes. Iron is used as tracer impurity in silicon to quantify the gettering rate. By fitting the experimental gettering kinetics by a diffusion-limited segregation gettering model, the blocking effects of the SiOx interlayers are quantified by a transport parameter. Both the oxide stoichiometry and pinhole density affect the effective transport of iron through SiOx interlayers. The oxide stoichiometry depends strongly on the oxidation method, while the pinhole density is affected by the activation temperature, doping concentration, doping technique, and possibly the dopant type as well. To enable a fast gettering process during typical high-temperature formation of the poly-Si/SiOx structures, a SiOx interlayer that is less stoichiometric or with a higher pinhole density is preferred.

KW - gettering

KW - iron

KW - polysilicon/oxide passivating contacts

KW - silicon oxide

KW - silicon solar cells

UR - http://www.scopus.com/inward/record.url?scp=85129175023&partnerID=8YFLogxK

U2 - 10.1002/aenm.202103773

DO - 10.1002/aenm.202103773

M3 - Article

AN - SCOPUS:85129175023

VL - 12

JO - Advanced energy materials

JF - Advanced energy materials

SN - 1614-6832

IS - 24

M1 - 2103773

ER -