Impurity Gettering in Polycrystalline‐Silicon Based Passivating Contacts—The Role of Oxide Stoichiometry and Pinholes. Issue 24 (1st May 2022)

• Record Type: Journal Article
• Authors: Yang, Zhongshu; Krügener, Jan; Feldmann, Frank; Polzin, Jana‐Isabelle; Steinhauser, Bernd; Le, Tien T.; Macdonald, Daniel; Liu, AnYao
• Is Part Of: Advanced energy materials. Volume 12:Issue 24(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-05-01
• Subjects: gettering -- iron -- polysilicon/oxide passivating contacts -- silicon oxide -- silicon solar cells; Energy harvesting -- Materials -- Periodicals; Energy conversion -- Materials -- Periodicals; Energy storage -- Materials -- Periodicals; Photovoltaics -- Periodicals; Fuel cells -- Periodicals; Thermoelectric materials -- Periodicals; 621.31
• DOI: 10.1002/aenm.202103773
• Languages: English
• ISSNs: 1614-6832

Abstract

Abstract: Polycrystalline‐silicon/oxide (poly‐Si/SiO x ) passivating contacts for high efficiency solar cells exhibit excellent surface passivation, carrier selectivity, and impurity gettering effects. However, the ultrathin SiO x interlayer can act as a diffusion barrier for metal impurities and this potentially slows down the overall gettering rate of the poly‐Si/SiO x structures. Herein, the factors that determine the blocking effects of the SiO x interlayers are identified and investigated by examining two general types of the SiO x interlayers: 1.3 nm ultrathin tunneling SiO x with negligible pinholes and 2.5 nm SiO x 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 SiO x interlayers are quantified by a transport parameter. Both the oxide stoichiometry and pinhole density affect the effective transport of iron through SiO x 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/SiO x structures, a SiO x interlayer that is less stoichiometric or with a higher pinhole density is preferred. Abstract : Heavily doped polycrystalline‐silicon/oxide (poly‐Si/SiO x ) passivating contacts gather Fe from the silicon wafer bulk to the poly‐Si gettering sink. Fe atoms either diffuse through the SiO x directly or transport via pinholes in the SiO x . Herein, the gettering kinetics to explore the role of the oxide stoichiometry and pinhole density on effective Fe diffusion through the SiO x interlayer is investigated and compared.