Local Structure of High Performance TiOx Electron‐Selective Contact Revealed by Electron Energy Loss Spectroscopy

Abstract

AbstractRecent increases in the power conversion efficiency of crystalline silicon (c‐Si) heterojunction (SHJ) solar cells are due to implementation of carrier‐selective contacts (CSCs) with high passivation performance and low contact resistivity. These electrical properties of CSCs significantly depend on the nature of the CSCs/c‐Si interface at the atomistic scale, and precise control of the interface with the SiOx interlayer is the key to obtaining superior electrical properties. It is shown that a TiOx/c‐Si structure with an interlayer prepared by nitric acid at room temperature shows the best performance among points with five different interlayer formation methods. The underlying mechanisms are investigated by combining high‐resolution transmission electron microscopy and electron energy loss (EEL) spectroscopy. The EEL spectra reveal that the Si:O ratio of an as‐deposited SiOx interlayer is nonstoichiometric (x < 2), which could contribute to lower contact resistivity. Furthermore, the as‐deposited SiOx leads to formation of a Ti containing SiOx layer with few oxygen vacancies after forming gas annealing, resulting in the significant enhancement of passivation performance. These results show that the control of the interlayer with atomistic scale is of crucial importance to realize higher power conversion efficiency of SHJ solar cells.