Comprehensive prediction of lead-free mixed-valence Cs2AgIAuIIIX6 (X = Cl, Br, I) halide double perovskites for high-efficiency photovoltaics.

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    • Abstract:
      • The structural stability, optoelectronic properties, and photovoltaic performance of lead-free mixed-valence Cs 2 AgIAuIIIX 6 (X = Cl, Br, I) are firstly disclosed. • The structural stability is validated by comprehensive theoretical calculations. • The studied perovskites exhibit appropriate optical band gaps (1.2 − 1.5 eV) for photovoltaic applications. • The predicted maximum efficiency of 30.3 % is achieved for Cs 2 AgIAuIIII 6. In light of their suitability for optoelectronic and photovoltaic devices, lead-free halide double perovskites (HDPs) have been extensively concerned in recent years. However, most HDPs have large and indirect band gaps (> 2 eV), which is unfavorable for perovskite solar cells. Here, the structural stability, optoelectronic response, and photovoltaic performance of mixed-valence HDPs Cs 2 AgIAuIIIX 6 (X = Cl, Br, I) have been theoretically examined. The thermodynamic, dynamical, and mechanical stability are verified in terms of the decomposition energy, phonon dispersion, and elastic constants. The computed indirect-gaps are 1.44 eV for Cs 2 AgIAuIIICl 6 , 1.25 eV for Cs 2 AgIAuIIIBr 6 , and 1.22 eV for Cs 2 AgIAuIIII 6 , respectively. These mixed-valence Cs 2 AgIAuIIIX 6 (X = Cl, Br, I) HDPs possess more suitable optical band gaps in comparison with that of Cs 2 AuIAuIIIX 6. The role of different metal cations in determining electronic properties is further elucidated. Furthermore, the optical analysis discloses that three mixed-valence HDPs exhibit high visible-light absorption coefficients. Additionally, the photovoltaic response of Cs 2 AgIAuIIIX 6 (X = Br, I) is further substantiated since the predicted efficiency is beyond 28 %. Overall, our study reveals that mixed-valence Cs 2 AgIAuIIIX 6 (X = Cl, Br, I) HDPs shows good stability and superior photovoltaic performance, which is an efficient candidate for single-junction perovskite solar cells. [ABSTRACT FROM AUTHOR]
    • Abstract:
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