Mixed Valence Perovskite Cs2Au2I6: A Potential Material for Thin-Film Pb-Free Photovoltaic Cells with Ultrahigh Efficiency

Abstract

New light is shed on the previously known perovskite material, Cs₂Au₂I₆, as a potential active material for high-efficiency thin-film Pb-free photovoltaic cells. First-principles calculations demonstrate that Cs₂Au₂I₆ has an optimal band gap that is close to the Shockley–Queisser value. The band gap size is governed by intermediate band formation. Charge disproportionation on Au makes Cs₂Au₂I₆ a double-perovskite material, although it is stoichiometrically a single perovskite. In contrast to most previously discussed double perovskites, Cs₂Au₂I₆ has a direct-band-gap feature, and optical simulation predicts that a very thin layer of active material is sufficient to achieve a high photoconversion efficiency using a polycrystalline film layer. The already confirmed synthesizability of this material, coupled with the state-of-the-art multiscale simulations connecting from the material to the device, strongly suggests that Cs₂Au₂I₆ will serve as the active material in highly efficient, nontoxic, and thin-film perovskite solar cells in the very near future.

Cs₂Au₂I₆ is an interesting perovskite material having mixed-valence Au centers. The current state-of-the-art multiscale simulation shows that this old-but-new material is highly advantageous as a lead-free and stable material for very thin-film perovskite solar cells (PSCs). This work is expected to inspire experimentalists to realize this new concept in PSCs based on mixed-valence perovskites.

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