Mechanism of Pressure-Driven Band Gap Evolutions in Lead-Free Halide Double Perovskites
Mechanism of Pressure-Driven Band Gap Evolutions in Lead-Free Halide Double Perovskites
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DOI：
10.1021/acs.jpcc.2c03250
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发表时间：
2022-06
期刊：
影响因子：
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通讯作者：
Lingjun He;Yuanhui Sun;M. Miao;Haiqing Lin
中科院分区：
文献类型：
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作者：
Lingjun He;Yuanhui Sun;M. Miao;Haiqing Lin
无铅卤化物双钙钛矿Cs2BBiCl6（B = Na, Ag）由于其无毒性和固有稳定性，在光电应用中具有潜在的替代品。有趣的是，它们的立方相的光致发光光谱显示，在压力下带隙的演变强烈依赖于b位金属。我们的第一性原理计算表明，这种独特的现象是由能带边缘的b位阳离子（Na和Ag）的轨道贡献引起的。与Na在cs2nabicl6中的3s价轨道对能带边缘态贡献不大相反，Ag在cs2agbicl6中由于Ag - cl键的成键-反键能分裂在费米能级以下的扩大，在压力下可以引起价带最大能的大幅向上移动。其他具有不同b位阳离子（K, Rb， Cu和Au）的双钙钛矿在+1价态表现出与cs2nabicl6和Cs2AgBiCl6相似的带隙演变，表明b位阳离子在无铅卤化物双钙钛矿的电子性质调节中起着关键作用。此外，我们的计算表明，cs2cubicl6和cs2aubicl6的光学吸收系数在可见光区域可以达到105cm - 1，并且可以通过外压进一步增强。我们的研究揭示了s/d块金属调控双钙钛矿带隙的机理，为高压下光电子带工程提供了指导。
Lead-free halide double perovskites Cs2BBiCl6(B = Na, Ag) are potential alternatives in optoelectronic applications because of their nontoxicity and intrinsic stability. Intriguingly, the photoluminescence spectra of their cubic phases revealed that the band gap evolution under pressure strongly depends on B-site metals. Our first-principles calculations demonstrate that this distinct phenomenon is caused by orbital contributions of B-site cations (Na versus Ag) at the band edges. In contrast to Na in Cs2NaBiCl6whose 3s valence orbitals contribute insignificantly to the band edge states, Ag in Cs2AgBiCl6can cause large upward shifts of the valence band maximum energy under pressure because of the enlargement of the bonding–antibonding energy split of Ag–Cl bonds below the Fermi level. Other double perovskites with different B-site cations (K, Rb, Cu, and Au) in the +1 valence state exhibit band gap evolutions similar to Cs2NaBiCl6and Cs2AgBiCl6, indicating that the B-site cation plays a critical role in regulating the electronic properties of lead-free halide double perovskites. Moreover, our calculations show that the optical absorbance coefficients of Cs2CuBiCl6and Cs2AuBiCl6can be as large as 105cm–1in the region of visible lights and could be further enhanced by external pressure. Our study reveals the mechanism of how s/d-block metals regulate the band gap of double perovskites and provides a guideline for the band engineering of optoelectronics under high pressure.