McIsaac Alexandra R, Goldzak Tamar, Van Voorhis Troy
Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States.
J Phys Chem Lett. 2023 Feb 9;14(5):1174-1181. doi: 10.1021/acs.jpclett.2c03317. Epub 2023 Jan 30.
Colloidal semiconductor nanocrystals have attracted much interest due to their unique optical properties, with applications ranging from displays to biomedical imaging. Nanocrystal optical properties depend on the structure of the surface, where defects can lead to traps. CdSe nanocrystals undergo surface reorganization, or self-healing, to eliminate defects, removing midgap traps from the band structure. However, the effect of this process on the optical spectrum is not well studied. Here, we show that self-healing not only eliminates midgap traps from the band structure but also brightens the spectrum and causes the excitonic states to emerge as the dominant features, in agreement with experimental annealing studies. We find that self-healing can lead to new traps like bonded Se-Se or Cd-Cd dimers, and their behavior is different from that of undercoordinated atom traps. These results suggest that eliminating traps requires a balance of allowing enough surface reorganization to eliminate undercoordinated atoms, but not so much that dimeric traps form.
胶体半导体纳米晶体因其独特的光学性质而备受关注，其应用范围涵盖从显示器到生物医学成像等领域。纳米晶体的光学性质取决于表面结构，表面缺陷会导致陷阱的产生。CdSe纳米晶体会经历表面重组或自我修复，以消除缺陷，从能带结构中去除带隙中间的陷阱。然而，这一过程对光谱的影响尚未得到充分研究。在此，我们表明自我修复不仅能从能带结构中消除带隙中间的陷阱，还能使光谱变亮，并使激子态成为主要特征，这与实验退火研究结果一致。我们发现自我修复会导致形成新的陷阱，如键合的Se-Se或Cd-Cd二聚体，它们的行为与配位不足的原子陷阱不同。这些结果表明，消除陷阱需要在允许足够的表面重组以消除配位不足的原子和避免形成二聚体陷阱之间取得平衡。
