Colloidal CdSe nanocrystals are inherently defective

Abstract

Colloidal CdSe nanocrystals (NCs) have shown promise in applications ranging from LED displays to medical imaging. Their unique photophysics depend sensitively on the presence or absence of surface defects. Using simulations, we show that CdSe NCs are inherently defective; even for stoichiometric NCs with perfect ligand passivation and no vacancies or defects, we still observe that the low energy spectrum is dominated by dark, surface-associated excitations, which are more numerous in larger NCs. Surface structure analysis shows that the majority of these states involve holes that are localized on two-coordinate Se atoms. As chalcogenide atoms are not passivated by any Lewis base ligand, varying the ligand should not dramatically change the number of dark states, which we confirm by simulating three passivation schemes. Our results have significant implications for understanding CdSe NC photophysics, and suggest that photochemistry and short-range photoinduced charge transfer should be much more facile than previously anticipated.

Defect Passivation in Lead‐Halide Perovskite Nanocrystals and Thin Films: Toward Efficient LEDs and Solar Cells

“…[ 1c , 2 ] They play a key role in controlling the optical, electronic, and structural properties of semiconductors, and thus affect a wide range of applications. [ 1a , 1d , 1f , 2a , 3 ] Although defects give rise to numerous advantages (e.g. active sites for photocatalysis), the traps they introduce in the band gap are detrimental to the optoelectronic performance of semiconductors.…”

“…In classical semiconductor systems, such as Si, GaAs, CdTe, CdSe, InP, and metal chalcogenides, a small population of defects can be extremely detrimental, as reflected in the substantial decrease in their intrinsic photoluminescence quantum yield (PLQY), carrier mobility, and stability. [ 1f , 5 ] However, interestingly, some semiconductors are defect‐tolerant, which means that it is possible to achieve low nonradiative recombination rates despite high densities of traps in the band gap. [ 1a , 2c , 6 ] Defect‐tolerant semiconductors were rare and were not widely studied until the recent serendipitous discovery of LHPs.…”

“…voids or wrinkles) [1c, 2] . They play a key role in controlling the optical, electronic, and structural properties of semiconductors, and thus affect a wide range of applications [1a,d,f, 2a, 3] . Although defects give rise to numerous advantages (e.g.…”

Defect Passivation in Lead‐Halide Perovskite Nanocrystals and Thin Films: Toward Efficient LEDs and Solar Cells

“…In classical semiconductor systems, such as Si, GaAs, CdTe, CdSe, InP, and metal chalcogenides, a small population of defects can be extremely detrimental, as reflected in the substantial decrease in their intrinsic photoluminescence quantum yield (PLQY), carrier mobility, and stability [1f, 5] . However, interestingly, some semiconductors are defect‐tolerant, which means that it is possible to achieve low nonradiative recombination rates despite high densities of traps in the band gap [1a, 2c, 6] .…”

Revealing the Surface Structure of CdSe Nanocrystals by Dynamic Nuclear Polarization-Enhanced 77Se and 113Cd Solid-State NMR Spectroscopy

“…DFT calculations have become one of the primary tools to predict structures of surface atoms, ligand binding modes and linking these to NC optoelectronic properties. [32][33][34][35][36][37][38][39] Many of the elements that make up the most investigated inorganic NCs have NMR-active isotopes. Consequently, magic angle spinning (MAS) solid-state NMR spectroscopy has found increasing applications in the study of both the bulk (interior) and surface structures of NCs.…”