Prospects of Chalcopyrite-Type Nanocrystals for Energy Applications

Abstract

are an emerging class of materials used in energy conversion systems, owing to their high absorption coefficients, nontoxicity, and appropriate band gaps. Their properties can be tuned by varying their size and composition, and they are characterized by peculiar photophysical properties due to a high density of intra band gap electronic states, which arise from defects in the crystal structure and from trap states at the surface. In this Perspective we first discuss optical and electrochemical studies, which give insight into the electronic structure of chalcopyrite nanocrystals. In the second part, their exploitation for energy conversion is highlighted, in particular their use in photovoltaics (with power conversion efficiencies already exceeding 10%) as well as in luminescent solar concentrators, photocatalytic systems, and thermoelectrics. Finally, we discuss current challenges in the chemistry and applications of the title compounds.

Biocompatible Semiconductor Quantum Dots as Cancer Imaging Agents

“…With very few exceptions, QDs are synthesized with wide band gap semiconductor shells that improve optical properties. QD synthesis and properties have been comprehensively reviewed by others (Zhong et al, Dubertret and co‐workers Kolny‐Olesiak and Weller, Gao and Rogach, Reiss and co‐workers, Gamelin and co‐workers, Prasad and co‐workers, and Ryan and co‐workers) and will therefore not be explained in great detail here. However, it is important to note that for a vast majority of biomedical applications, QDs are nanoparticles with a fluorescent core, semiconductor shell, surface functionalization that enables their dispersion in water, and functionalized with other biomolecules to target specific proteins expressed on the surface of the cells of interest ( Figure ).…”

“…As a result, multiple QD populations targeting different molecules or tissues can be used to simultaneously visualize a variety of cancer‐related biomarkers or events using a single excitation source. Because the narrowest emission bands have traditionally been associated with toxic II–VI Cd(Se,Te) QDs, significant effort has recently focused on the production of biocompatible ternary I–III–VI chalcogenide QDs such as Cu–In–S and Cu–In–Se, which normally have emission widths on the order of 80–150 nm due to the presence of multiple recombination channels . Klimov and co‐workers recently demonstrated the ability to narrow the PL emission width of a single dot down to 60 meV (≈20 nm) through epitaxial coating of the CuInS 2 core with a relatively thick (up to six layers) ZnS shell, which was thought to reduce the positioning heterogeneity of Cu defect‐related emission centers in the encapsulated QD .…”

Raman characterization of Cu2ZnSnS4 nanocrystals: phonon confinement effect and formation of CuxS phases

“…The direct-bandgap chalcogenide-based compounds offer a promising solar cell alternative which benets from high light absorption in comparison to Si. 2,3 One such material is kesterite Cu 2 ZnSnS 4 (CZTS). This material has a direct bandgap of 1.4-1.6 eV and a high absorption coefficient of above 10 4 cm À1 , and all its constituents are Earth-abundant and affordable, and have low toxicity.…”

Unravelling the Correlation of Electronic Structure and Carrier Dynamics in CuInS2 Nanoparticles

“…(1, 4) They have high extinction coefficient, emission quantum yield, and appropriate band gaps, which have rendered these nanocrystals desirable as light-harvesting and charge separation materials in photovoltaics and photocatalysis. (8)(9)(10)(11)(12)(13) As the functions of CIS in these applications are mainly dictated by their light-absorbing and emission behaviors, it is essential to develop a deep understanding of the excited state dynamics of CIS. Indeed, there are a handful of recent reports that have explored the excited state properties of CIS or CIS-based nanocrystals using timeresolved spectroscopic techniques.…”