Development of nonstoichiometric CuInS₂ as a light-harvesting photoanode and catalytic photocathode in a sensitized solar cell

One-Pot Synthesis of High-Quality AgGaS2/ZnS-based Photoluminescent Nanocrystals with Widely Tunable Band Gap

Herein, we present a facile colloidal method to synthesize the high-quality AgGaS₂ nanocrystals (NCs) within 2 min via exploiting the high-reactivity S precursor and then extend this synthetic strategy to the preparation of AgGaS₂/ZnS core-shell NCs by a one-pot method without prior purification of AgGaS₂ core. The as-synthesized samples were structurally characterized to confrim the formation of AgGaS₂/ZnS core-shell NCs. The energy band gap of the AgGaS₂/ZnS NCs can be effectively tunable from 2.98 to 2.83 eV by the control of their nonstoichiometry and further continuously decreases to 1.90 eV by the preparation of alloyed AgGa_xIn_1-xS₂/ZnS NCs (1 ≤ x ≤ 0). Benefitting from the efficient band gap modulations, the photoluminescence (PL) colors of the AgGaS₂-based NCs can cover almost the whole visible region from blue (460 nm) to red (671 nm). Our work demonstrates the one-pot synthesis of AgGaS₂/ZnS core-shell NCs and their band gap engineering, which is of crucial in scalability toward industrial application and in tailoring optical characteristics of I-III-VI₂ materials.

Colloidal Phase-Change Materials: Synthesis of Monodisperse GeTe Nanoparticles and Quantification of Their Size-Dependent Crystallization

Phase-change memory materials refer to a class of materials that can exist in amorphous and crystalline phases with distinctly different electrical or optical properties, as well as exhibit outstanding crystallization kinetics and optimal phase transition temperatures. This paper focuses on the potential of colloids as phase-change memory materials. We report a novel synthesis for amorphous GeTe nanoparticles based on an amide-promoted approach that enables accurate size control of GeTe nanoparticles between 4 and 9 nm, narrow size distributions down to 9-10%, and synthesis upscaling to reach multigram chemical yields per batch. We then quantify the crystallization phase transition for GeTe nanoparticles, employing high-temperature X-ray diffraction, differential scanning calorimetry, and transmission electron microscopy. We show that GeTe nanoparticles crystallize at higher temperatures than the bulk GeTe material and that crystallization temperature increases with decreasing size. We can explain this size-dependence using the entropy of crystallization model and classical nucleation theory. The size-dependences quantified here highlight possible benefits of nanoparticles for phase-change memory applications.

Compound Copper Chalcogenide Nanocrystals

This review captures the synthesis, assembly, properties, and applications of copper chalcogenide NCs, which have achieved significant research interest in the last decade due to their compositional and structural versatility. The outstanding functional properties of these materials stems from the relationship between their band structure and defect concentration, including charge carrier concentration and electronic conductivity character, which consequently affects their optoelectronic, optical, and plasmonic properties. This, combined with several metastable crystal phases and stoichiometries and the low energy of formation of defects, makes the reproducible synthesis of these materials, with tunable parameters, remarkable. Further to this, the review captures the progress of the hierarchical assembly of these NCs, which bridges the link between their discrete and collective properties. Their ubiquitous application set has cross-cut energy conversion (photovoltaics, photocatalysis, thermoelectrics), energy storage (lithium-ion batteries, hydrogen generation), emissive materials (plasmonics, LEDs, biolabelling), sensors (electrochemical, biochemical), biomedical devices (magnetic resonance imaging, X-ray computer tomography), and medical therapies (photochemothermal therapies, immunotherapy, radiotherapy, and drug delivery). The confluence of advances in the synthesis, assembly, and application of these NCs in the past decade has the potential to significantly impact society, both economically and environmentally.

Two Distinct Transitions in Cu(x)InS2 Quantum Dots. Bandgap versus Sub-Bandgap Excitations in Copper-Deficient Structures

Cu-deficient CuInS2 quantum dots (QDs) synthesized by varying the [Cu]:[In] ratio allow modulation of optical properties as well as identification of the radiative emission pathways. Absorption and emission spectral features showed a strong dependence on the [Cu]:[In] ratio of CuxInS2 QDs, indicating two independent optical transitions. These effects are pronounced in transient absorption spectra. The bleaching of band edge absorption and broad tail absorption bands in the subpicosecond-nanosecond time scale provide further evidence for the dual optical transitions. The recombination process as monitored by photoemission decay indicated the involvement of surface traps in addition to the bandgap and sub-bandgap transitions. Better understanding of the origin of the optical transitions and their influence on the photodynamics will enable utilization of ternary semiconductor quantum dots in display and photovoltaic devices.

One-pot synthesis of colloidal Cdx:CuInS2 quaternary quantum dots used as sensitizers in photovoltaic cells

Cd_x:CuInS₂ quaternary QDs were obtained in a one-pot reaction; these quaternary QDs exhibited enhanced photovoltaic performance compared to pristine CuInS₂ ternary QDs.

Molecular engineering of quinoxaline dyes toward more efficient sensitizers for dye-sensitized solar cells

N-annulated perylene-containing quinoxaline sensitizer (NIQ4) displays remarkable performance in light harvesting, electron injection, and dye regeneration.