Synthesis of large CZTSe nanoparticles through a two-step hot-injection method

Abstract

Grain boundaries in Cu 2 ZnSn(S x Se 1-x ) 4 (CZTSSe) thin films act as a defect that reduces the mobility of the charges. Hence one way to improve the performance of these thin film solar cells is to increase the grain size in the films. Most of the synthesis methods published so far for CZTSSe colloidal nanoparticles can achieve a general size distribution range from 5-20 nm. This is where the particle size will saturate for most recipes used today. The assumption is that uniform size distribution is good for grain growth in a thin film but based on packing considerations, an optimal mixture of large and small nanoparticles that can easily be dispersed in non-polar solvents could be better. Cu 2 ZnSnS 4 (CZTS) and Cu 2 ZnSnSe 4 (CZTSe) nanoparticles are synthesized using the hot-injection method with oleylamine, trioctylphosphine, and hexadecane as the solvents. Selenium (Se) is introduced in the liquid phase to encourage grain growth -liquid selenization. This eliminates the need to anneal the film in a Se-containing atmosphere and allows for a more environmentally friendly process with lower temperatures and shorter annealing times. We show that a good dispersion can be achieved by choosing suitable surfactant molecules, solvents and precursors, and by controlling the initial monomer concentration. Additionally, we show how our new synthesis route can be utilized to achieve targeted ratios of CZTS and CZTSe nanoparticles to be used for mixed-phase CZTSSe thin films.

Efficient Perovskite Light‐Emitting Diodes Using Polycrystalline Core–Shell‐Mimicked Nanograins

“…We simply described the crystal growth mechanism by applying the LaMer model (Figure S7b, Supporting Information). In the fast A‐NCP process for OSN film formation, the rapid co‐evaporation of the solvents by volatile nonpolar CF induces 1) the simultaneous nucleation at most nucleation sites, 2) a short nucleation period, which induces uniform reactant reaction, to form small and uniform nanograins, 3) a short‐time and instantaneous crystal growth that forms the small grains by the crystallographically misoriented faces related to grain boundaries, 4) a rapid consumption of limited precursor concentration, and 5) the instant rinsing of DMSO, the precursor diffusion medium. Therefore, fast A‐NCP effectively causes the crystal growth to cease before secondary crystal growth by Ostwald ripening.…”

“…However, the TPBI molecules inside the quasi‐films are gradually rinsed away during A‐NCP so that some portion of them cannot stay at grain boundaries and thus they do not have a uniform additive distribution throughout the film. On the other hand, fast A‐NCP can effectively confine the additives in MAPbBr 3 :TPBI quasi‐film by instant DMSO rinsing for fast crystallization (Figure S7, Supporting Information) …”

Synthesis of Cu 2 ZnSnSe 4 thin‐film solar cells from nanoparticles by a non‐vacuum mechanical ball milling and rapid thermal processing

“…However, these complicated vacuum deposition techniques present difficulties in materials utilisation efficiency and expensive in instruments. Alternatively, solution‐based non‐vacuum deposition techniques, such as electrodeposition [10, 11], metal salt solutions [12–15], nanoparticle inks [16–20] and hydrazine‐based inks [21, 22], do not necessarily require high vacuum facilities. For example, Ilari et al [15] developed a metal salt‐based solution deposition method to synthesis CZTSe photovoltaic cells with an efficiency of 2.76%, in which monoethanolamine and 2‐methoxyethanol were used as organic stabiliser and solvent.…”

“…The nanoparticle inks deposition methods involve depositing nanoparticles inks and then selenisation in H 2 Se or Se vapour [23]. The CZTSe nanoparticles were often synthesised by hot injection methods or solvothermal methods, which require complicated Schlenk‐line reaction vessel and intricate post‐processing [19, 24]. The hydrazine‐based inks processing is an attractive way to the synthesis of carbon‐free CZTSSe thin films.…”

Cu2ZnSn(S,Se)4 thin-films prepared from selenized nanocrystals ink

“…However, hot-injection synthesis is not appropriate for scaling-up process due to its difficulty in controlling the monomer release. 21 To overcome these drawbacks, researchers have recently instigated the heating up synthesis of CZTS NCs, 22,23 but they used expensive materials, multi-solvents and high reaction temperature > 250 C, which is not suitable for the industrial applications. Therefore, it is necessary to develop a simple and low-cost synthesis method for CZTS NCs to fabricate and commercialize thin lm solar cell devices.…”