Intrinsic Amorphous Silicon Bilayers for Effective Surface Passivation in Silicon Heterojunction Solar Cells: A Comparative Study of Interfacial Layers

• Published in: Physica status solidi. A, Applications and materials science Vol. 218; no. 9
• Main Authors: Sai, Hitoshi, Hsu, Hung-Jung, Chen, Po-Wei, Chen, Pei-Ling, Matsui, Takuya
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01.05.2021
• Subjects: Amorphous silicon; Chemical vapor deposition; Comparative studies; Fourier transform infrared spectroscopy; Heterojunctions; hydrogen; Hydrogen bonds; Infrared absorption; Microstructure; Parameter modification; Passivity; Photovoltaic cells; plasma chemical vapor deposition; Process parameters; Silicon; silicon solar cells; Solar cells; surface passivation
• ISSN: 1862-6300; 1862-6319
• DOI: 10.1002/pssa.202000743

The impact of intrinsic amorphous silicon bilayers in amorphous silicon/crystalline silicon (a‐Si:H/c‐Si) heterojunction solar cells is investigated. Intrinsic a‐Si:H films with a wide range of film densities and hydrogen contents are prepared via a plasma‐enhanced chemical vapor deposition (PECVD) technique by modifying various process parameters. For silicon heterojunction (SHJ) solar cells with a‐Si:H films applied as single i‐layers, the resulting surface passivation at the a‐Si:H/c‐Si interface is poor. However, surface passivation is significantly improved by applying intrinsic bilayers, which are composed of a porous interfacial layer (≈2 nm) and an overlying dense layer (≈8 nm). The microstructure factor R* of the interfacial a‐Si:H layer, which is related to the SiH bond microstructure and determined by infrared absorption spectroscopy, closely correlates to the surface passivation capability of the bilayers. A variety of PECVD process parameters (temperature, pressure, or precursor gas species) can be utilized to grow an interfacial layer for good surface passivation, provided that its R* is controlled within a suitable range. This indicates that R* is a key universal parameter for optimizing i‐bilayers and realizing high‐efficiency SHJ solar cells. Herein, silicon heterojunction solar cells with intrinsic amorphous silicon (a‐Si:H) bilayers are investigated. The microstructure factor R* of the interfacial a‐Si:H layer, which is related to the SiH bond microstructure, closely correlates to the surface passivation, and must be controlled within a suitable range for realizing high‐efficiency silicon heterojunction solar cells.