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.

Colloidal metal chalcogenide nanoparticles have emerged as a promising hydrazine-free route for the fabrication of solution processed electronic devices. While a wide variety of synthetic pathways have been developed for these nanomaterials, typical colloidal syntheses rely on the use of metal salts as precursors, which contain anionic impurities such as halides, nitrates, acetates, and so forth, that may incorporate and alter the electrical properties of the targeted nanoparticles. In this report, the recent advances in aminethiol chemistry and its unique ability to dissolve pure metals, chalcogens, and metal chalcogenides is expanded upon for the fabrication of metal chalcogenide nanoparticles. Alkylammonium metal thiolate species are easily formed upon addition of monoamine and dithiol to elemental Cu, In, Ga, Sn, Zn, Se, or metal chalcogenides such as Cu 2 S and Ag 2 S. These species were then used directly for the synthesis of colloidal nanoparticles without the need for any additional purification. The thermal decomposition pathway of one such representative alkylammonium metal thiolate species was studied, verifying that only metal chalcogenides and volatile byproducts are formed, providing a flexible route to compositionally uniform, phase pure, and anionic impurity-free colloidal nanoparticles. Synthetic methods were developed from these precursors to yield pure phase colloidal nanoparticles of binary, ternary, and quaternary materials and their alloys including In 2 S 3 , (In x Ga 1−x ) 2 S 3 , CuInS 2 , CuIn(S x Se 1−x ) 2 , Cu(In x Ga 1−x )S 2 , Cu 2 ZnSnS 4 , and AgInS 2 . Successful synthesis with various experimental methods such as heat up, hot injection, and microwave assisted solvothermal reactions were also demonstrated, showing the flexibility and greater scope for this new synthesis route.

Solution processing of CuInSe2/CuInGaSe2 (CISe/CIGSe) photovoltaic devices from a non-hydrazine based routes have been studied for the past few years and a significant improvement in device performance has been achieved...

Atomic layer deposition (ALD) of conformal AlF3 coatings onto both flat silicon substrates and high-voltage LiNi0.5Mn0.3Co0.2O2 (NMC) Li-ion battery cathode powders was investigated using a Al(CH3)3/TaF5 precursor combination. This optimized approach employs easily handled ALD precursors, while also obviating the use of highly toxic HF(g). In studies conducted on planar Si wafers, the film's growth mode was dictated by a competition between the desorption and decomposition of Ta reaction byproducts. At T ≥ 200 °C, a rapid decomposition of the Ta reaction byproducts to TaC led to continuous deposition and high concentrations of TaC in the films. A self-limited ALD growth mode was found to occur when the deposition temperature was reduced to 125 °C, and the TaF5 exposures were followed by an extended purge. The lower temperature process suppressed conversion of TaFx(CH3)5−x to nonvolatile TaC, and the long purges enabled nearly complete TaFx(CH3)5−x desorption, leaving behind the AlF3 thin films. NMC cathode powders were coated using these optimized conditions, and coin cells employing these coated cathode particles exhibited significant improvements in charge capacity fade at high discharge rates.

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