Synthesis And Optical Properties Of Multinary Silver Chalcogenide Semiconductor Nanocrystals

Multinary copper or silver chalcogenide semiconductor nanocrystals(NCs)have exhibited a promising potential application in biological imaging,light-emitting diodes,solar cells and photocatalysis due to their unique optoelectronic properties.In the past few years,AgInS2(AIS)semiconductor NCs have attracted much attention due to their tunable optical band gap and high carrier mobility,and the synthesis of AIS nanocrystals have drawn the researchers,interests.The current synthetic methods of AIS semiconductor NCs mainly focus on the thermal decomposition of various metals and sulfur complexes or the direct reaction of metal cations with sulfur under specific ligands.However,most of these studies focus on the luminescence properties of AIS semiconductor NCs,few studies on the growth mechanism were reported.In this work,seeded-mediated methods were developed to prepare ternary AgInS2(AIS)and quaternary Ag-In-Zn-S(AIZS)nanocrystals through partial cation exchange with In3+and Zn2+ions using Ag2S as seeds.Their growth mechanism,optical properties and the self-assembly behavior were studied,and the application of AIZS nanocrystals in quantum-dot light-emitting diodes(QLEDs)was explored.(1)One-pot colloidal method was developed to synthesize binary Ag2S nanocrystals with different size,which were then acted as the seeds to prepare different-sized AIS NCs through the cation exchange of In3+ions.The temporal-evolution of the morphology and crystal structure was studied,and the heterostructured Ag2S-AIS nanocrystals as intermediates were formed during the growth process of AIS nanocrystals,which played an important role in the formation of AIS nanocrystals.Afterwards,the effects of Ag/In feeding ratios on the optical band gap and photoluminescence(PL)maximum of AIS nanocrystals were studied,and phase change and photoluminescence improvement took place with an increase of the reaction time.In addition,the self-assembly behavior of AIS nanocrystals was studied,which could self-assemble into fingerprint-like structure due to the synergistic effects of the dosage of dodecanethiol and In3+ions.(2)Seeded-mediated methods were developed to prepare quaternary Ag-In-Zn-S nanocrystals through the partial cation exchange of Zn2+ions.The incorporation of Zn2+ions into AIS NCs resulted in the widening of the optical band gap and the shift of the PL maximum to the higher energy as well as the enhancement of the absolute PL quantum yields(PLQYs).The maximum absolute PLQYs of AIZS nanocrystals could reach up 58%.The time-resolved PL spectroscopy was used to study the PL decay dynamics of the AIS and AIZS nanocrystals,and the PL emission was related to the recombination of the surface-related states,intrinsic defects and donor-acceptor(D-A)pairs.The ternary and quaternary Ag-based semiconductor nanocrystals had long-lived excitons,which may hold a promising application in the fields of energy conversion.In addition,we used the quaternary AIZS nanocrystals as the emitting layer to fabricate QLEDs by using the all-solution method,which exhibited a low turn-on voltage of 3.4 V and a maximum brightness of about 114 cd/m2.