Muchun Guo,Ming Liu,Jianbo Zhu,Yuke Zhu,Fengkai Guo,Wei Cai,Yongsheng Zhang,QinYong Zhang,Jiehe Sui
Chemical bonds determine electron and phonon transport in solids. Tailoring chemical bonding in thermoelectric materials causes desirable or compromise thermoelectric transport properties. In this work, taking an example of CaMg 2 Bi 2 with covalent and ionic bonds, density functional theory calculations uncover that element Zn, respectively, replacing Ca and Mg sites cause the weakness of ionic and covalent bonding. Electrically, Zn doping at both Ca and Mg sites increases carrier concentration, while the former leads to higher carrier concentration than that of the latter because of its lower vacancy formation energy. Both doping types increase density-of-state effective mass but their mechanisms are different. The Zn doping Ca site induces resonance level in valence band and Zn doping Mg site promotes orbital alignment. Thermally, point defect and the change of phonon dispersion introduced by doping result in pronounced reduction of lattice thermal conductivity. Finally, combining with the further increase of carrier concentration caused by Na doping and the modulation of band structure and the decrease of lattice thermal conductivity caused by Ba doping, a high figure-of-merit ZT of 1.1 at 823 K in Zn doping Ca sample is realized, which is competitive in 1–2–2 Zintl phase thermoelectric systems.
Qianjin Wang,Zhilin Xiang,Peizhi Yang,Yingkai Liu,Qiuhong Tan
Metal halide perovskites recently have emerged as a promising candidate for photodetection due to their exceptional photoelectric performance. However, the high dark current in these materials has hindered their practical application to imaging. In this study, a novel halogen-mixed CsPbIBr 2 microwire photodetector that has a remarkable reduction of dark current by over 100-fold (compared to CsPbBr 3 ), along with a substantial increase in photocurrent, which yields a significantly improved on/off ratio of 6.56 × 10 4 , is developed. More importantly, the halogen-mixed perovskite photodetector exhibits enhanced photodetection performance, including a high responsivity of 133 A W −1 and a remarkable specific detectivity of 4.02 × 10 12 Jones even under ultraweak light conditions as low as 4.5 nW cm −2 . More specifically, high-resolution images are successfully obtained under ultraweak light conditions. The combined analysis of experimental results and first-principles calculation attribute the excellent performance of the CsPbIBr₂ microwire photodetector to a significant reduction in dark current by suppressing ion migration and increasing carrier effective mass, and a remarkable increase in photocurrent resulting from reduced bandgap and enhanced light absorption, as compared to CsPbBr 3 . This research represents a significant advancement in the development of high-performance 1D perovskite-based photodetectors, with promising implications for ultra-weak light imaging applications.
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