Assessing the stability of p⁺ and n⁺ polysilicon passivating contacts with various capping layers on p-type wafers

verfasst von

Chukwuka Madumelu, Yalun Cai, Christina Hollemann, Robby Peibst, Bram Hoex, Brett J. Hallam, Anastasia H. Soeriyadi

Abstract

Polysilicon (poly-Si)-on-oxide passivating contact structures (POLO/TOPCon) enable high-efficiency solar cells as they simultaneously provide a very high level of surface passivation and a high conductance for either electrons or holes. The ease of incorporation with existing manufacturing lines and their tolerance for high-temperature processing has increased the wide acceptance of this structure in the PV industry. In this report, we explore the effects of short high-temperature annealing required for effective hydrogenation and formation of ohmic screen-printed contacts across a wide temperature range (636 °C–846 °C) on the stability of passivating contact structures. We study this on p-type c-Si substrates with phosphorus-doped (n-type) or boron-doped (p-type) polysilicon contacts capped with either an AlO_x or SiN_x coating. Our experimental results show that irrespective of the poly-Si doping type, AlO_x-capped samples suffer a loss in surface passivation across the investigated temperature range, while SiN_x-capped samples show an improvement at lower annealing temperatures. Above 744 °C, severely ruptured blisters occur for the samples coated with a SiN_x layer, leading to lift-off of the poly layer in extreme cases, and in all cases, significant surface passivation losses, up to 99%. A study of the long-term stability of these fired samples under 1-sun illumination @ 140 °C shows that they suffer from both bulk and surface-like instabilities. Two degradation cycles were observed: the first, a boron-oxygen light-induced degradation (BO-LID) observed after 5 min, with capture cross-section ratios of 15.8–19.2, and a slower secondary degradation, similar to light and elevated temperature-induced degradation (LeTID), with maximum degradation reached after ∼ 14 days. The presence of a silicon nitride layer does not appear to influence the kinetics of post-degradation recovery. Our results suggest that the effect of firing may be influenced by the polarity of the bulk c-Si or perhaps the chemistry of the SiN_x film and highlight that passivating contact structures based on p-type c-Si may offer better long-term stability than those based on n-type c-Si.

Organisationseinheit(en)

Institut für Materialien und Bauelemente der Elektronik

Externe Organisation(en)

University of New South Wales (UNSW)
Institut für Solarenergieforschung GmbH (ISFH)
ITP Renewables
University of Oxford

Typ

Artikel

Journal

Solar Energy Materials and Solar Cells

Band

253

ISSN

0927-0248

Publikationsdatum

05.2023

Publikationsstatus

Veröffentlicht

Peer-reviewed

Ja

ASJC Scopus Sachgebiete

Elektronische, optische und magnetische Materialien, Erneuerbare Energien, Nachhaltigkeit und Umwelt, Oberflächen, Beschichtungen und Folien

Ziele für nachhaltige Entwicklung

SDG 7 – Erschwingliche und saubere Energie

Elektronische Version(en)

https://doi.org/10.1016/j.solmat.2023.112245 (Zugang: Offen)