Controlling Morphology in Polycrystalline Films by Nucleation and Growth from Metastable Nanocrystals

Abstract

Solution processing of polycrystalline compound semiconductor thin film using nanocrystals as a precursor is considered one of the most promising and economically viable routes for future large-area manufacturing. However, in polycrystalline compound semiconductor films such as CuZnSnS (CZTS), grain size, and the respective grain boundaries play a key role in dictating the optoelectronic properties. Various strategies have been employed previously in tailoring the grain size and boundaries (such as ligand exchange) but most require postdeposition thermal annealing at high temperature in the presence of grain growth directing agents (selenium or sulfur vapor with/without Na, K, etc.) to enlarge the grains through sintering. Here, we show a different strategy of controlling grain size by tuning the kinetics of nucleation and the subsequent grain growth in CZTS nanocrystal thin films during a crystalline phase transition. We demonstrate that the activation energy for the phase transition can be varied by utilizing different shapes (spherical and nanorod) of nanocrystals with similar size, composition, and surface chemistry leading to different densities of nucleation sites and, thereby, different grain sizes in the films. Additionally, exchanging the native organic ligands for inorganic surface ligands changes the activation energy for the phase change and substantially changes the grain growth dynamics, while also compositionally modifying the resulting film. This combined approach of using nucleation and growth dynamics and surface chemistry enables us to tune the grain size of polycrystalline CZTS films and customize their electronic properties by compositional engineering.

Chemical Energy Release Driven Lithiophilic Layer on 1 m2 Commercial Brass Mesh toward Highly Stable Lithium Metal Batteries

“…Moreover, the negative Gibbs (Δ G < 0) energy released from the oxidation reaction drives the replacement reaction between CuO and Zn, which shows the presence of a ZnO layer on the surface (eq 1, Supporting Information). − Thus, we speculate that the released negative Gibbs energy drives the surface diffusion during the thermal treatment in air, which is achieved from the oxidation reaction and following replacement reaction. , A mass loading of about 1.02 mg cm –2 (the calculation and discussion in the experimental section of the Supporting Information) and thickness of about several micrometers ZnO layer on the surface of the brass mesh was successfully prepared using a simple thermal treatment. Furthermore, series of oxidation experiments at various temperatures were conducted to study the morphology evolution process and composition on the surface.…”

Polymorph Evolution Mechanisms and Regulation Strategies of Lithium Metal Anode under Multiphysical Fields

“…In addition, there are also some unique methods to fabricate the lithiophilic coatings over hosts. Heating brass mesh (Zn–Cu alloy) at 300 °C in air produces a compact and even ZnO layer on the surface, which is ascribed to the atom diffusion on the surface driven by the Gibbs free energy decrement of the oxidation reaction (Figure c). ,, By applying the anode, the lithiophilic property gets improved a lot and the cells are able to stably run for 500 cycles at the current density of 2 mA cm –2 .…”

Thermal Stability of Semiconductor Nanocrystal Solids: Understanding Nanocrystal Sintering and Grain Growth

“…It was previously observed that wurtzite-to-kesterite phase transition at elevated temperature led to enhanced grain growth in w-CZTS nanorods. ,, Here, we demonstrate the generality of this phenomenon for various nanomaterials synthesized as metastable polymorphs by colloidal methods. Figure a shows the change of P-XRD patterns of zb-CdSe NCs with (N 2 H 5 ) 2 In 2 Se 4 ligands upon heating.…”

“…Sintering of micron and submicron powders is routinely used to improve mechanical properties, to increase electrical and thermal conductivity in ceramics, in powder metallurgy, for fabricating thermoelectric materials, and so on. − On the other hand, preventing sintering of catalytically active metal clusters is an active area of research in heterogeneous catalysis. − Colloidally synthesized NCs bridge the size gap between micron-sized ceramic powders and metal clusters, which are typically smaller than 2 nm. Sintering and grain growth of ALD-passivated PbS NCs, superlattices of PbSe NCs, CIGS NCs, and CZTS nanorods have been studied; ,,− however, a systematic understanding of NC sintering and grain growth is largely lacking. Sintering studies of as-synthesized colloidal NCs are complicated by organic surface ligands that separate inorganic NC cores at room temperature but desorb and decompose upon heating .…”