Growth of Multinary Copper-Based Sulfide Shells on CuInSe₂ Nanocrystals for Significant Improvement of Their Near-Infrared Emission

Abstract

A range of different copper-based sulfide shells, such as CuInS 2 , CuInZnS 2 , CuInS 2-x Se x , and CuInZnS 2-x Se x , have been grown on CuInSe 2 (CISe) nanocrystals (NCs) in order to improve their photoluminescence quantum yield (PLQY). Starting from initial CISe core NCs with PLQY of 0.4%, the deposition of the CuInS 2 shell has increased the PLQY to 4.5%, while introducing Zn or Se elements into the CuInS 2 shell to form cation-alloyed CuInZnS 2 or anion-alloyed CuInS 2-x Se x shells improved their PLQYs to 8% and 11%, respectively. Limitations on PLQY for the mentioned shell materials were related to the lattice mismatch with the CISe core material, and the band gap alignment in the core/shell NCs for quasi type-II nanostructures. This could be mitigated by growing a multinary CuInZnS 2-x Se x shell on the CISe core NCs, which resulted in further improvement of their PLQY to 20% for the emission centered at 920 nm. This study offers guidance for the rational selection of copper-based sulfide shell materials that are able to significantly improve the PLQY of heavy-metal free CISe NCs in the near-infrared spectral range of 834−1028 nm, which is relevant for biological labeling, optoelectronics, and sensing.

Nucleation Temperature‐Dependent Synthesis of Polytypic CuInSe2 Nanostructures with Variable Tetrapod‐Like and Core‐Shell Morphologies

“…The elemental composition of the CISe NCs estimated from the EDX analysis provides atomic ratio of Cu : In:Se equal to 1 : 1.15 : 1.7. Such nonstoichiometric, cationrich composition was also reported in previous studies, [38,43] and may be related to the cation terminations of NC surface, or the disordering of wurtzite-like phase. Crystal structure and phase composition of tetrapods were probed by X-ray diffraction (XRD).…”

“…As a heavy‐metal free compound semiconductor, ternary CuInSe 2 (often abbreviated as CISe) exhibits several merits, such as high light absorption coefficient (10 −5 cm −1 ), large Bohr exciton radius (10.6 nm), and relative narrow bandgap (1.05 eV), which renders it promising for applications in near‐infrared light emitting diodes, solar cells, solar concentrators, and in bioimaging [29–33] . Several synthetic procedures were developed towards CISe NCs, and their nucleation and growth pathways were explored [34–38] . Due to the large difference in reactivities of In 3+ and Cu + cations, the formation of Cu based ternary NCs is often accompanied by formation of copper chalcogenides at the beginning of the reaction; this may be followed by an appearance of Cu 2 S−In 2 S 3 or Cu x Se−InSe as intermediate phases during cation exchange reactions [34,39] Most of the produced CISe NCs exhibited a single crystal structure with a chalcopyrite (CP) phase.…”

“…[29][30][31][32][33] Several synthetic procedures were developed towards CISe NCs, and their nucleation and growth pathways were explored. [34][35][36][37][38] Due to the large difference in reactivities of In 3 + and Cu + cations, the formation of Cu based ternary NCs is often accompanied by formation of copper chalcogenides at the beginning of the reaction; this may be followed by an appearance of Cu 2 SÀ In 2 S 3 or Cu x SeÀ InSe as intermediate phases during cation exchange reactions [34,39] Most of the produced CISe NCs exhibited a single crystal structure with a chalcopyrite (CP) phase. Only few works [40][41][42] reported synthesis of CISe NCs with WZ crystal structure; they typically employed diselenide precursors (RÀ SeÀ SeÀ R, where R = alkyl, allyl, benzyl, or phenyl) at a relatively high temperature (> 200 °C).…”

Near infrared bioimaging and biosensing with semiconductor and rare-earth nanoparticles: recent developments in multifunctional nanomaterials

“…Another class of copper-based luminescent SNCs is that of I-III-IV CuIn(S,Se) 2 . Their synthesis has been developed relatively recently, hence there is ample room for improvement in terms of control of their morphology, growth of core/shell structures, 45 and size dispersion. The latter is an issue when aiming for biological applications, due to the different fate experienced in the body by NPs of different sizes.…”

“…Another class of copper-based luminescent SNCs is that of I-III-IV CuIn(S,Se) 2 . Their synthesis has been developed relatively recently, hence there is ample room for improvement in terms of control of their morphology, growth of core/shell structures, 45 Despite these results, an important limitation of CuIn(S,Se) 2 -based SNCs is the difficulty to push their emission beyond 1300 nm. 48 On the contrary, this could be accomplished with Inbased binary SNCs containing pnicogens (P, As, Sb), whose emission can span the whole 500-1600 nm range.…”