Although metal halide double perovskites A₂B(I)B(III)X₆ are expected as nontoxic alternatives for lead halide perovskites, recent studies have shown that only Tl(I)–Bi(III) and In(I)–Bi(III) bromides are thermodynamically stable and possess optoelectronic properties suitable for photovoltaic absorbers. Here, we show, through density functional theory calculations, that Tl–Bi and In–Bi bromide double perovskites exhibit significantly different semiconducting behaviors due to the different energy levels of the highest-occupied pseudoclosed s² orbitals of Tl(I) and In(I). While Tl–Bi double perovskites can exhibit semiconducting p-type properties, In–Bi bromide double perovskites exhibit metallic p-type ones regardless of the synthesis condition due to the extremely low formation energy of In vacancy. Such difference makes Tl–Bi bromide double perovskites suitable for optoelectronic applications, but not In–Bi bromide double perovskites. Furthermore, there is a high probability for In to substitute a Bi site, forming a local In–In bromide double perovskite structure with a lower local conduction band minimum, detrimentally affecting the open circuit voltage of In–Bi bromide double perovskite-based thin film solar cells.

中文翻译：

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伪闭合s ²轨道对于Tl–Bi和In–Bi溴化物双钙钛矿之间不同的本征空穴生成的作用

尽管金属卤化物双钙钛矿A ₂ B（I）B（III）X ₆有望作为卤化钙钛矿铅的无毒替代品，但最近的研究表明，只有Tl（I）-Bi（III）和In（I）-Bi（ III）溴化物是热力学稳定的，并具有适用于光伏吸收器的光电特性。在这里，我们表明，通过密度泛函理论计算，即铊Bi和In-碧溴化双钙钛矿具有显著不同的半导体行为，由于占用最高pseudoclosed S的不同能级^2个轨道铊（I）和在（一世）。Tl-Bi双重钙钛矿可以表现出半导体的p型特性，而In-Bi溴化物双钙钛矿可以表现出金属p的特性。In空位的形成能极低，因此，与合成条件无关，都具有高能效。这种差异使T1-Bi溴化双钙钛矿适用于光电应用，但In-Bi溴化双钙钛矿却不适用。此外，In极有可能取代Bi位点，从而形成具有较低局部导带最小值的局部In-In溴化物双钙钛矿结构，从而不利地影响In-Bi溴化物双钙钛矿基薄膜的开路电压。太阳能电池。