Quantum dot-sensitized solar cells based on directly adsorbed zinc copper indium sulfide colloids

Role of Intrinsic Defects in Enhancing the Photoabsorption Capability of CuZn2AlSe4

As a promising candidate for low-cost and eco-friendly thin-film photovoltaics, the emerging quaternary chalcogenide based solar cells have experienced rapid advances over the past decade. Here, we propose quaternary semiconducting chalcogenides CuZn₂AlSe₄ (CZASe) through cross-substitutions (cation mutations). The nonexistence of imaginary modes in the entire Brillouin zone of CZASe represents the inherent dynamic stability of the system. The electronic, optical, and defect properties of stannite CZASe quaternary semiconducting material was systematically investigated using density functional theory calculations. We have found that the chemical-potential control is very important for growing good-quality crystals and also to avoid secondary-phase formations such as ZnSe, Al₂ZnSe₄, and Cu₃Se₂. The observed p-type conductivity is mainly due to antisite defect Cu_Zn, which has the lowest formation energy with a relatively deeper acceptor level than that of the Cu vacant site (V_Cu). The electronic band structures of vacancies and antisite defects by means of hybrid functional calculations show energy band shifting and energy band narrowing or broadening, which eventually tunes the optical band gap and improves the solar energy-conversion performance of semiconducting CZASe. Our results suggest that the stannite CZASe quaternary chalcogenides could be promising candidates for the efficient earth-abundant thin-film solar cells.

Enhancing Loading Amount and Performance of Quantum-Dot-Sensitized Solar Cells Based on Direct Adsorption of Quantum Dots from Bicomponent Solvents

Intrinsically weak interaction between oil-soluble quantum dots (QDs) and TiO₂ in a direct adsorption process limits QD loading and the performance of QD-sensitized solar cells (QDSCs). Herein, the underlying chemistry and mechanisms governing QD adsorption on TiO₂ were studied to improve QD loading and cell performance. Experimental results indicate that solvent polarity plays the crucial role in determining QD loading. Compared with single-component solvents, substantially greater QD loading can be realized at the critical point (CP) of bicomponent solvents, where QDs become metastable and start to precipitate. Through this strategy, average efficiency of 12.24% was obtained for ZCISe QDSCs, which is comparable to those based on the capping ligand induced self-assembly route. This report demonstrates the great potential of bicomponent solvents at the CP for high QD loading and excellent cell performance and presents a platform for assembling functional composites with the use of different nanocrystals and substrates.

Hot injection synthesis of CuInS2 nanocrystals using metal xanthates and their application in hybrid solar cells

Copper indium sulfide nanocrystals with sizes of 3–4 nm were synthesized from metal xanthates in a hot injection reaction. After ligand exchange, their performance as acceptors in polymer/nanocrystal hybrid solar cells was evaluated.

Solar Paint from TiO2 Particles Supported Quantum Dots for Photoanodes in Quantum Dot-Sensitized Solar Cells

The preparation of quantum dot (QD)-sensitized photoanodes, especially the deposition of QDs on TiO₂ matrix, is usually a time-extensive and performance-determinant step in the construction of QD-sensitized solar cells (QDSCs). Herein, a transformative approach for immobilizing QD on the TiO₂ matrix was developed by simply mixing the as-prepared oil-soluble QDs with TiO₂ P25 particles suspension for a period as short as half a minute. The solar paint was prepared by adding the TiO₂/QD composite in a binder solution under ultrasonication. The QD-sensitized photoanodes were then obtained by simply brushing the solar paint on a fluorine-doped tin oxide substrate followed by a low-temperature annealing at ambient atmosphere. Sandwich-structured complete QDSCs were assembled with the use of Cu₂S/brass as counter electrode and polysulfide redox couple as an electrolyte. The photovoltaic performance of the resulting Zn-Cu-In-Se (ZCISe) QDSCs was evaluated after primary optimization of the QD/TiO₂ ratio as well as the thicknesses of photoanode films. In this proof of concept with a simple solar paint approach for photoanode films, an average power conversion efficiency of 4.13% (J _sc = 11.11 mA/cm², V _oc = 0.590 V, fill factor = 0.631) was obtained under standard irradiation condition. This facile solar paint approach offers a simple and convenient approach for QD-sensitized photoanodes in the construction of QDSCs.

ZnO–TiO2 composites and ternary ZnTiO3 electrospun nanofibers: the influence of annealing on the photocatalytic response and reusable functionality

By using understanding from the construction of composites to ternary-phased 1D NFs, we design a layout for ZnO–TiO₂ composite and ZnTiO₃ electrospun NFs with different band structures as a function of the annealing temperature with the possibility of defect states.

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.

Toward the Facile and Ecofriendly Fabrication of Quantum Dot-Sensitized Solar Cells via Thiol Coadsorbent Assistance

This paper reports a facile and environmentally friendly approach to the preparation of highly efficient quantum dot-sensitized solar cells (QDSSCs) based on a combination of aqueous CuInS2 quantum dots (QDs) and thiol coadsorbents. The photovoltaic properties of the QDSSCs were found to be dependent on the type and concentration of the thiol coadsorbent. The incorporation of thiol coadsorbents results in improved JSC and VOC because (1) they provide disulfide reductants during the QD sensitization process and (2) the coadsorbent molecules are anchored on the TiO2 surface, thus affecting the movement of the conduction band of TiO2. To the best of the our knowledge, this is the first demonstrated use of various thiol coadsorbents as reducing agents in the fabrication of high-efficiency QDSSCs. CuInS2 QDSSCs fabricated with the assistance of thioglycolic acid coadsorbents exhibited efficiencies as high as 5.90%, which is 20 times higher than that of the control device without thiol coadsorbents (0.29%). In addition, the photovoltaic properties of a device fabricated using the colloidal CuInS2 QDs coated with different bifunctional linkers were investigated for comparison. The versatility of this facile fabrication process was demonstrated in the preparation of solar cells sensitized with aqueous AgInS2 or CdSeTe QDs. The AgInS2 QDSSC showed a conversion efficiency of 2.72%, which is the highest reported for Ag-based metal sulfides QDSSCs thus far.

Room temperature synthesis of CuInS2 nanocrystals

Herein, we investigate a synthetic approach to prepare copper indium sulfide nanocrystals at room temperature.

A new family of wurtzite-phase Cu2ZnAS4−x and CuZn2AS4 (A = Al, Ga, In) nanocrystals for solar energy conversion applications

A new family of semiconductors Cu₂ZnAS_4−x and CuZn₂AS₄ (A = Al, Ga, In) that absorb strongly at visible wavelengths has been synthesized as nanocrystals.

Optimizing Photovoltaic Response by Tuning Light-Harvesting Nanocrystal Shape Synthesized Using a Quick Liquid-Gas Phase Reaction

The electron recombination lifetime in a sensitized semiconductor assembly is greatly influenced by the crystal structure and geometric form of the light-harvesting semiconductor nanocrystal. When such light harvesters with varying structural characteristics are configured in a photoanode, its interface with the electrolyte becomes equally important and directly influences the photovoltaic efficiency. We have systematically probed here the influence of nanocrystal crystallographic structure and shape on the electron recombination lifetime and its eventual influence on the light to electricity conversion efficiency of a liquid junction semiconductor sensitized solar cell. The light-harvesting cadmium sulfide (CdS) nanocrystals of distinctly different and controlled shapes are obtained using a novel and simple liquid-gas phase synthesis method performed at different temperatures involving very short reaction times. High-resolution synchrotron X-ray diffraction and spectroscopic studies respectively exhibit different crystallographic phase content and optical properties. When assembled on a mesoscopic TiO2 film by a linker molecule, they exhibit remarkable variation in electron recombination lifetime by 1 order of magnitude, as determined by ac-impedance spectroscopy. This also drastically affects the photovoltaic efficiency of the differently shaped nanocrystal sensitized solar cells.

High catalytic activity of a PbS counter electrode prepared via chemical bath deposition for quantum dots-sensitized solar cells

A PbS counter electrode (CE) has been fabricated by a chemical bath deposition method, and can function as a counter electrode with high catalytic activity for quantum dots-sensitized solar cells (QDSSCs).