I-III-VI2 and II-VI/I-III-VI2 Alloyed Nanocrystals and Their Heterostructures: Synthesis, Characterization and Potential Applications

I-II-VI2 and II-VI/I-III-VI2 materials are some of the most promising candidates for photovoltaic and photocatalytic applications due to their unique structural, optical and electrical properties. In this study, we synthesize CuInSe2 (CIS) and CuIn1-xGa xSe2 nanocrystals with different morphologies and compositions using a simple solution method by changing the growth conditions. The optical property of the CIGS with different Ga content has been investigated, and a band gap energy dependence on the Ga concentration is found. Using the synthesized single crystalline CIGS nanocrystals, we fabricate CIGS thin films using simple and low-cost drop-casting method. By changing different preparation parameters, the film quality for obtaining uniform and crack-free CIGS film is fabricated. Post treatments are also attempted to further imporve the transport property of the films by either soaking the films into an EDT solution or annealing them at a high temperature.;In this study, we further demonstrate the morphology differentiation in Au-CIGS nanostructures by designing the growth route. Taking CIGS nanoparticles (nps) as the seeds, Au-CIGS side-by-side nps are obtained, while reversing the growth sequence (using Au nps for seeding) leads to the formation of Au-core/CIGS-shell heterostructures. The formation mechanisms of these heterostructured Au-CIGS nps are discussed in detail based on the nanoparticle microstructure analysis. The different configuration of the heterostructured Au-CIGS nps is found to affect the surface plasmon resonance of Au, as suggested by the optical absorption measurements taken from the corresponding samples.;On the other hand, we introduce a new material system: II-VI and I-III-VI 2 alloyed nanocrystals, such as ZnS-CuInS2 ((CuIn)x Zn2(1--x)S2:CIZS) alloyed nanoparticles. CIZS has attracted much researcher's attention due to the wide tunable band gap energy (from 1.5 to 3.5 eV) and the potential visible light driven water splitting applications. In this material system, we start from synthesizing a series of (CuIn)xZn2(1--x)S2 (CIZS) using simple solution based methods with oleylamine as the surfactant. The band gap energy can be tuned by adjusting the composition of CIZS from x=0 to x=1. Taking Au nanoparticles as seeds, Au/CuInS2 core/shell nanoparticles are obtained. However, when Zn source is added in the core shell synthesis process, only partially capped Au particles by (CuIn)xZn 2(1--x)S2 are obtained. The formation mechanisms of these heterostructured Au/CIZS nanoparticles are discussed in detail based on the microstructure analysis.