Department of Chemistry

• The full article entitled “Hydrogen Plasma Treatment Compensates for the Intrinsic Defects in Cs₂AgBiBr₆ Thin Films” can be found at the Journal of Physical Chemistry C website at https://pubs.acs.org/doi/10.1021/acs.jpcc.4c05773
• Authors: Heng-Chi Chu, Chieh-Ming Hung, Hsin-Chen Huang, Shih-Chang Weng, Bi-Hsuan Lin, Song Yang, Yu-Hao Wu, Kai-Hsin Chang, Jing-Jong Shyue, Pi-Tai Chou*, and Chang-Ming Jiang*

Halide double perovskite materials have garnered significant attention in the past decade as ideal alternatives to lead-based perovskites due to their low toxicity and high stability, finding broad applications in photovoltaic and light-emitting devices, and Cs₂AgBiBr₆ represents one of the most promising materials among them. However, its wide optical bandgap and low carrier mobility pose challenges for practical applications. A potential strategy involves introducing B-site disorder to enhance its visible light absorption, thereby improving its efficiency as a photovoltaic material. Nevertheless, such disorder inevitably leads to deep-level Ag-on-Bi antisite defects, causing non-radiative recombination losses.

This collaborative study between Assistant Professor Chang-Ming Jiang's and Professor Pi-Tai Chou’s research groups demonstrates that hydrogen plasma post-treatment can effectively compensate for the B-site antisite defects in Cs₂AgBiBr₆, significantly increasing its self-trapped exciton emission lifetime and enhancing its photoluminescence intensity by nearly tenfold (see Figure 1). The research team found that the n-type characteristics of the material were markedly enhanced after hydrogen treatment, accompanied by notable changes in the bonding environment of Bi and Ag. Additionally, temperature-dependent spectroscopy and X-ray diffraction analysis allowed for an in-depth investigation of the complex interactions between hydrogen and Cs₂AgBiBr₆ double perovskites. However, below the cubic-to-tetragonal phase transition temperature, hydrogen instead acts as a non-radiative recombination center, losing its defect-compensation ability. This study highlights the critical role of hydrogen doping in Cs₂AgBiBr₆ materials while underscoring the potential of hydrogen plasma post-treatment in the development of novel optoelectronic devices.

Figure 1. (a) Photoluminescence spectra measured using 375 nm (3.3 eV) excitation from pristine and hydrogen plasma-treated Cs₂AgBiBr₆ films. (b) Dynamics of the photo-induced absorbance signal at 1.65 eV (750 nm) probe energy. The solid line represents the fitting results using a triexponential decay function. (c) Schematic comparison of the valence band (VB) and conduction band (CB) energetics between pristine and hydrogenated Cs₂AgBiBr₆ films.