Toward Bright Colloidal Near-Infrared Emitters: Surface Passivation of 2D PbSe Nanoplatelets by Metal Halides

Abstract

Colloidal 2D PbSe nanoplatelets (NPLs) are promising near- and short wave-infrared emitters for optoelectronic applications at telecommunication wavelengths. However, their photoluminescence quantum yield (PLQY) is limited by the ubiquitous presence of surface-related trap states. Here, we apply a treatment of colloidal PbSe NPLs with different metal halides (MX2, M = Zn, Cd, Pb; X = F, Cl, Br, I) to improve their emission brightness. A surface passivation of the NPLs by PbI2 leads to the best results with a strongly increased PLQY (27% for PbSe NPLs emitting at 0.98 eV (1265 nm) and up to 61% for PbSe NPLs emitting at 1.25 eV (989 nm)). Simultaneously, the full width at half-maximum of the NPL photoluminescence decreased by 10% after the treatment. X-ray photoelectron spectroscopy and complementary surface treatment of PbSe NPLs with organic halides reveal the combined passivating role of both X-type binding halides X– and Z-type binding metal halides MX2 in enhancing the optical properties of the PbSe NPLs. Our results emphasize the potential of 2D PbSe NPLs for efficient emission tailored for the application in fiber optics.

Metal-Dictated Reactivity of Z-Type Ligands to Passivate Surface Defects on CdSe Nanocrystals

“…56 Biesterfelt et al observed the greatest PLQY increase of 2D PbSe NPLs after treatment with PbI 2 and the greatest PLQY decrease after treatment with CdF 2 . 23 The results for CdSe NCs presented here show that Cd-based ligands are more effective at passivating surface defects than Pb-based ligands. Thus, in both studies, the Z-type ligand native to the NC material yields the brightest NC.…”

“…Biersterfield and co-workers noted that CdF 2 -modified PbSe nanoplatelets (NPLs) exhibit half the PL quantum yield (PLQY) of pristine NPLs, yet the PLQY doubles for PbI 2modified NPLs. 23 Likewise, Greaney et al observed a different photoresponse between CdCl 2 -, CdBr 2 -, and CdI 2 -modified CdSe NCs. 20 Both studies highlight the potential use of nanomaterials in optoelectronic applications, but achieving trap-free nanomaterials is predicated on the judicious choice of a Z-type ligand.…”

“…Surface defect passivation by Z-type ligands has a profound impact on the electronic structure of NCs and is often used in postsynthetic reactions to modulate NC properties. ,− Several groups have demonstrated that control of the NC stoichiometry, through the addition or removal of Z-type ligands, modulates the electronic properties of NCs. ,,,− In 2015, Busby et al demonstrated that a stoichiometric Cd:Se surface increased the rate of hole trapping compared to a cadmium-rich NC . A nonlinear relationship between stoichiometry and PL yield suggested that not all undercoordinated Se ions serve as hole trap states.…”

“…While there are many examples in the literature that report surface trap passivation by Z-type ligands to increase NC optical and electronic properties, ,− there are exceptions. Biersterfield and co-workers noted that CdF 2 -modified PbSe nanoplatelets (NPLs) exhibit half the PL quantum yield (PLQY) of pristine NPLs, yet the PLQY doubles for PbI 2 -modified NPLs . Likewise, Greaney et al observed a different photoresponse between CdCl 2 -, CdBr 2 -, and CdI 2 -modified CdSe NCs .…”

Electroluminescence and Plasmon-Assisted Directional Photoluminescence from 2D HgTe Nanoplatelets

“…Infrared 2D colloidal materials are driven by narrow band gap semiconductors such as lead − and mercury − chalcogenides. These two classes of materials have very different growth mechanisms.…”