A mild hydrothermal route to synthesis of CZTS nanoparticle inks for solar cell applications

Abstract

Cu2ZnSnS4 (CZTS) is a promising thin film absorber material for low cost solar cell applications. Its absorption coefficient (∼ 104 cm‐1), crystal structure and band gap energies (∼1.5 eV) are similar to those of Cu(In,Ga)Se2 (CIGS), one of the most studied and flourishing thin film solar cell absorber materials. However, unlike CIGS, which requires the expensive and rare elements; In and Ga, CZTS is composed of reasonably priced and abundant elements like Zn and Sn. In the present investigation, kesterite CZTS nanoparticle inks were obtained by a hydrothermal process using Cu, Zn and Sn chlorides, and Na sulfide. The synthesized CZTS nanoparticles were characterized using optical absorption, X‐ray powder diffraction (XRD), energy dispersive spectroscopy (EDS), micro‐Raman spectroscopy, high‐resolution transmission electron microscopy (HRTEM), and X‐ray photoelectron spectroscopy (XPS). The optical and morphological properties demonstrated that the prepared nanoparticles have strong absorption in 300−550 nm range with band gap energy of 1.55 eV with an average particle size of 20 nm. The X‐ray and micro‐Raman analysis revealed that the synthesized CZTS nanoparticles have the phase pure kesterite structure. We believe that our synthetic method will be helpful for low‐cost and efficient thin film photovoltaic technology. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Aqueous Synthesis of Cu2ZnSnSe4 Nanocrystals

“…Various methods for the fabrication of CZTSSe thin films have been developed, including quinary sputtering and CZTSSe nanoparticle deposition; , however, the bulk of the literature has focused on a two-step process of depositing pure CZTS or CZTSe films followed by selenization and/or sulfurization at high temperature under toxic atmospheres to form the mixed CZTSSe phase. ,− The deposition of CZTS and CZTSe films can be achieved by the decomposition of molten salts, − reactive sputtering, − electroplating, − vapor deposition, − precursor solution deposition, − and nanoparticle ink sintering. − Of these, nanoparticle routes are among the most promising because of their potential to be inexpensive and scalable, while maintaining superior phase and compositional control when compared to nonsolution-based approaches. Although CZTS nanoparticle routes, including green and scalable syntheses, have been widely reported, ,− reports related to CZTSe nanoparticles are much more scarce. − , CZTSe nanoparticle syntheses typically involve the use of toxic solvents such as hydrazine,<...…”

Aqueous Synthesis of High-Quality Cu2ZnSnS4 Nanocrystals and Their Thermal Annealing Characteristics

“…Quaternary I 2 -II-IV-VI 4 compound copper zinc tin sulfide (CZTS) is regarded as a promising photovoltaic material due to its excellent optoelectronic properties, tunable band gap, and earth-abundant elemental composition . Various methods have been reported for the deposition of CZTS thin films, including the decomposition of molten salts, , reactive sputtering, , electroplating, , vapor deposition, , precursor solution deposition, − and nanoparticle ink sintering. − Of these methods, the approach using CZTS nanoparticle inks is one of the most promising, commonly achieving efficiencies over 8.5%, ,− with the highest-efficiency nanoparticle-based CZTS solar cells reported to date (11.1%) being fabricated using a hydrazine-based synthesis route . This success is largely due to the better phase and compositional control achieved through solution processing, compared to the alternative synthesis approaches.…”

“…However, synthesis routes for the production of high-quality CZTS nanoparticles typically involve the use of toxic solvents and extensive postsynthesis processing to remove organic impurities. − ,,− , These are clearly undesirable when considering that reproducibility and scale-up are essential for commercial production, which requires the minimization of hazards and additional processing steps. While existing “greener” CZTS nanoparticle syntheses based on water and ethanol dispersions overcome the risks associated with using toxic hydrazine, ,,− ,, eliminating organic contaminants, which are usually present as an excess of aliphatic ligands used to achieve homogeneous dispersions of nanocrystals, remains a challenge. Furthermore, incomplete combustion of these organic ligands also forms insulating layers at interfaces following thermal annealing, generating trap states that enhance carrier recombination .…”

Novel Evaporation Process for Deposition of Kesterite Thin Films Synthesized by Solvothermal Method

“…Kesterite was rst reported by Ito and Nakazawa in 1988 [2]. Research on methods to prepare kesterite thin lms can be classi ed into three types: (1) Research whose purpose is to synthesize materials, for example, nanoparticles [3][4][5]. (2) Research about deposition of material once it is synthesized.…”