The solution processing of Cu(In,Ga)(S,Se)2 photovoltaics from colloidal nanoparticles has long suffered from deleterious carbonaceous residues originating from long chain native ligands. This impurity carbon has been observed to hinder grain formation during selenization and leave a discrete residue layer between the absorber layer and the back contact. In this work, organic and inorganic ligand exchanges were investigated to remove tightly bound native oleylamine ligands from Cu(In,Ga)S2 nanoparticles, thereby removing the source of carbon contamination. However, incomplete ligand removal, poor colloidal stability, and/or selective metal etching were observed for these methods. As such, an exhaustive hybrid organic/inorganic ligand exchange was developed to bypass the limitations of individual methods. A combination of microwave-assisted solvothermal pyridine ligand stripping followed by inorganic capping with diammonium sulfide was developed and yielded greater than 98% removal of native ligands via a rapid process. Despite the aggressive ligand removal, the nanoparticle stoichiometry remained largely unaffected when making use of the hybrid ligand exchange. Furthermore, highly stable colloidal ink formulations using nontoxic dimethyl sulfoxide were developed, supporting stable nanoparticle mass concentrations exceeding 200 mg/mL. Scalable blade coating of the ligand-exchanged nanoparticle inks yielded remarkably smooth and microcrack free films with an RMS roughness less than 7 nm. Selenization of ligand-exchanged nanoparticle films afforded substantially improved grain growth as compared to conventional nonligand-exchanged methods, yielding an absolute improvement in device efficiency of 2.8%. Hybrid ligand exchange nanoparticle-based devices reached total area power conversion efficiencies of 12.0%, demonstrating the feasibility and promise of ligand-exchanged colloidal nanoparticles for the solution processing of Cu(In,Ga)(S,Se)2 photovoltaics.
Chalcogenide perovskites, including BaZrS3, have been suggested as highly stable alternatives to halide perovskites. However, the synthesis of chalcogenide perovskites has proven to be a significant challenge, often relying on excessively high temperatures and methods that are incompatible with device integration. In this study, we developed a solution-based approach to the deposition of BaZrS3. This method utilizes a combination of a soluble barium thiolate and nanoparticulate zirconium hydride. Following solution-based deposition of the precursors and subsequent sulfurization, BaZrS3 can be obtained at temperatures as low as 500 °C. Furthermore, this method was extended to other chalcogenide perovskite (BaHfS3) and perovskite-related (BaTiS3) materials.
Growing concerns regarding the safety, flammability and hazards posed by Li-ion systems have led to research on alternative rechargeable metal-ion electrochemical storage technologies. Among the most notable of these are Na-ion supercapacitors and batteries, motivated, in part, by the similar electrochemistry of Li and Na ions. However, sodium ion batteries (SIBs) come with their own set of issues, especially the large size of the Na + ion, its relatively sluggish kinetics and low energy densities. This makes the development of novel materials and appropriate electrode architecture of absolute significance. Transition metal dichalcogenides (TMDs) have attracted a lot of attention in this regard due to their relative ease of exfoliation, diverse morphologies and architectures with superior electronic properties. Here, we study the electrochemical performance of Mo-based two-dimensional (2D) layered TMDs (e.g. MoS 2 , MoSe 2 and MoTe 2 ), exfoliated in a superacid, for battery and supercapacitor applications. The exfoliated TMD flakes were interfaced with reduced graphene oxide (rGO) to be used as composite electrodes. Electron microscopy, elemental mapping and Raman spectra were used to analyse the exfoliated material and confirm the formation of 2D TMD/rGO layer morphology. For supercapacitor applications in aqueous electrolyte, the sulfide-based TMD (MoS 2 ) exhibited the best performance, providing an areal capacitance of 60.25 mF cm −2 . For SIB applications, TMD electrodes exhibited significantly higher charge capacities than the neat rGO electrode. The initial desodiation capacities for the composite electrodes are 468.84 mAh g −1 (1687.82 C g −1 ), 399.10 mAh g −1 (1436.76 C g −1 ) and 387.36 mAh g −1 (1394.49 C g −1 ) for MoS 2 , MoSe 2 and MoTe 2 , respectively. Also, the MoS 2 and MoSe 2 composite electrodes provided a coulombic efficiency of near 100 % after a few initial cycles.
Chalcogenide perovskites are promising semiconductor materials with attractive optoelectronic properties and appreciable stability, making them enticing candidates for photovoltaics and related electronic applications. Traditional synthesis methods for these materials have long suffered from high‐temperature requirements of 800–1000 °C. However, the recently developed solution processing route provides a way to circumvent this. By utilizing barium thiolate and ZrH2, this method is capable of synthesizing BaZrS3 perovskite at modest temperatures (500–600 °C), generating crystalline domains on the order of hundreds of nanometers in size. Herein, a systematic study of this solution processing route is done to gain a mechanistic understanding of the process and to supplement the development of device quality fabrication methodologies. A barium polysulfide liquid flux is identified as playing a key role in the rapid synthesis of large‐grain BaZrS3 perovskite at modest temperatures. Additionally, this mechanism is successfully extended to the related BaHfS3 perovskite. The reported findings identify viable precursors, key temperature regimes, and reaction conditions that are likely to enable the large‐grain chalcogenide perovskite growth, essential toward the formation of device‐quality thin films.
Chalcogenide perovskites have garnered interest for applications in semiconductor devices due to their excellent predicted optoelectronic properties and stability. However, high synthesis temperatures have historically made these materials incompatible with the creation of photovoltaic devices. Here, we demonstrate the solution processed synthesis of luminescent BaZrS3 and BaHfS3 chalcogenide perovskite films using single‐phase molecular precursors at sulfurization temperatures of 575 °C and sulfurization times as short as one hour. These molecular precursor inks were synthesized using known carbon disulfide insertion chemistry to create Group 4 metal dithiocarbamates, and this chemistry was extended to create species, such as barium dithiocarboxylates, that have never been reported before. These findings, with added future research, have the potential to yield fully solution processed thin films of chalcogenide perovskites for various optoelectronic applications.
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