Copper–indium–selenide (CISe) quantum dots (QDs) are a promising alternative to the toxic cadmium- and lead-chalcogenide QDs generally used in photovoltaics due to their low toxicity, narrow band gap, and high absorption coefficient. Here, we demonstrate that the photovoltaic performance of CISe QD-sensitized solar cells (QDSCs) can be greatly enhanced simply by optimizing the thickness of ZnS overlayers on the QD-sensitized TiO2 electrodes. By roughly doubling the thickness of the overlayers compared to the conventional one, conversion efficiency is enhanced by about 40%. Impedance studies reveal that the thick ZnS overlayers do not affect the energetic characteristics of the photoanode, yet enhance the kinetic characteristics, leading to more efficient photovoltaic performance. In particular, both interfacial electron recombination with the electrolyte and nonradiative recombination associated with QDs are significantly reduced. As a result, our best cell yields a conversion efficiency of 8.10% under st...

Highly Efficient Copper–Indium–Selenide Quantum Dot Solar Cells: Suppression of Carrier Recombination by Controlled ZnS Overlayers

Photocatalytic hydrogen evolution is a promising technique for the direct conversion of solar energy into chemical fuels. Colloidal quantum dots with tunable band gap and versatile surface properties remain among the most prominent targets in photocatalysis despite their frequent toxicity, which is detrimental for environmentally friendly technological implementations. In the present work, all-inorganic sulfide-capped InP and InP/ZnS quantum dots are introduced as competitive and far less toxic alternatives for photocatalytic hydrogen evolution in aqueous solution, reaching turnover numbers up to 128,000 based on quantum dots with a maximum internal quantum yield of 31%. In addition to the favorable band gap of InP quantum dots, in-depth studies show that the high efficiency also arises from successful ligand engineering with sulfide ions. Due to their small size and outstanding hole capture properties, sulfide ions effectively extract holes from quantum dots for exciton separation and decrease the physical and electrical barriers for charge transfer.

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Efficient photocatalytic hydrogen evolution with ligand engineered all-inorganic InP and InP/ZnS colloidal quantum dots.

This review is focused on new concepts and recent progress in the development of three major quantum dot (QD) based optoelectronic devices: photovoltaic cells, photodetectors and LEDs In each application, we discuss recent champion devices with a range of architectures and discuss in detail the chronological steps taken to produce significant improvements in efficiency We consider this relative to developments in colloidal quantum dots and their effects on these devices, covering alloyed, doped and core/shell QDs, quaternary Cu–Zn–In–S QDs, graphene and silicon QDs, and the wide range of highly promising NIR QDs The diverse range of novel device designs is examined, including all-quantum dot devices, ternary hybrid compounds, plasmonic enhancements, and nano-heterojunction architectures In addition, we analyse recent advances in charge transport layers, blocking layers, nanostructured photoanode fabrication and the importance of QD surface treatments Throughout, we emphasise the use of hybrid composite materials including combinations of QDs with metal oxides, plasmonic nanoparticles, graphene and others Finally, this review provides an analysis of prospects of these important selected quantum dot-based optoelectronic devices

Colloidal quantum dots for optoelectronics

Room temperature single-photon emission and lasing for all-inorganic colloidal perovskite quantum dots

Quantum dot-sensitized solar cells (QDSCs), as promising candidates for cost-effective photoelectrochemical solar cells, have attracted much attention due to their characteristic properties such as processability at low cost, feasibility to control light absorption spectrum in a wide region, and possibility of multiple electron generation with a theoretical conversion efficiency up to 44%. QDSCs have analogous structures to dye-sensitized solar cells typically consisting of semiconductor photoanodes sensitized with quantum dots (QDs), redox electrolytes, and counter electrodes (CEs). Much effort has been dedicated to optimizing each component of QDSCs for higher device performance. In this review, recent advances of photoanodes with various architectures, QDs with tunable band gaps, electrolytes in liquid, quasi-solid or solid state, and CEs with great electrocatalytic activity for QDSCs will be highlighted. We aim to elaborate the rational strategies in material design for QDSC applications. Finally, the conclusion and future prospects emphasize the key developments and remaining challenges for QDSCs.

Recent advances in quantum dot-sensitized solar cells: insights into photoanodes, sensitizers, electrolytes and counter electrodes

Enhancement of the charge transfer rate in CdSe quantum dot (QD) sensitized solar cells is one of the most important criteria determining cell efficiency. We report a novel strategy for enhancing charge transfer by exchanging the native, long organic chain to an atomic ligand, S2–, with a simple solid exchange process. S2–-ligand exchange is easily executed by dipping the CdSe QDs sensitized photoanode into a formamide solution of K2S. The results show that this exchange process leads to an enhancement of the electronic coupling between CdSe QD and TiO2 by removing the insulating organic barrier to charge transfer, while maintaining its quantum confined band structure. This treatment significantly increases the charge transfer rate at the interfacial region between CdSe QDs and TiO2 as well as between the CdSe QDs and Red/Ox coupling electrolyte, as verified by time-resolved photoluminescence and electrochemical impedance spectroscopy measurements. Finally, the S2–-treated photoanode exhibits a much highe...

Enhanced charge transfer kinetics of CdSe quantum dot-sensitized solar cell by inorganic ligand exchange treatments.

Light absorption and electron injection are important criteria determining solar energy conversion efficiency. In this research, monodisperse CdSe quantum dots (QDs) are synthesized with five different diameters, and the size-dependent solar energy conversion efficiency of CdSe quantum dot sensitized solar cell (QDSSCs) is investigated by employing the atomic inorganic ligand, S2–. Absorbance measurements and transmission electron microscopy show that the diameters of the uniform CdSe QDs are 2.5, 3.2, 4.2, 6.4, and 7.8 nm. Larger CdSe QDs generate a larger amount of charge under the irradiation of long wavelength photons, as verified by the absorbance results and the measurements of the external quantum efficiencies. However, the smaller QDs exhibit faster electron injection kinetics from CdSe QDs to TiO2 because of the high energy level of CBCdSe, as verified by time-resolved photoluminescence and internal quantum efficiency results. Importantly, the S2– ligand significantly enhances the electronic coup...

Nanocrystal Size-Dependent Efficiency of Quantum Dot Sensitized Solar Cells in the Strongly Coupled CdSe Nanocrystals/TiO2 System

Solution processed CuSbS 2 films for solar cell applications

Tailoring Absorber Thickness and the Absorber-Scaffold Interface in CdSe-Coated ZnO Nanowire Extremely Thin Absorber Solar Cells

The extremely thin absorber (ETA) solar cell architecture can enable higher efficiencies than planar cells for absorbers that have low carrier lifetimes or mobilities. Efficient charge separation requires that interfacial electron and hole transfer proceed much faster than the recombination lifetime of photoexcited carriers. In this work, transient absorption spectroscopy was employed to measure these ultrafast photophysical processes in CdSe-coated ZnO nanowire ETA cells and model planar films. At low pump fluences, carrier lifetime was controlled by Shockley–Read–Hall and surface recombination. Annealing the electrodeposited CdSe films increased the lifetime 50-fold, to >1 ns as measured by transient absorption spectroscopy, which correlated to improved ETA cell performance. Interfacial electron transfer from the CdSe coating into the ZnO nanowires occurred 3 orders of magnitude faster, within 1 ps, independent of the presence or absence of an interfacial CdS buffer layer. Interfacial hole transfer to t...

Michael E. Edley

Papers

Enhanced charge transfer kinetics of CdSe quantum dot-sensitized solar cell by inorganic ligand exchange treatments.

Nanocrystal Size-Dependent Efficiency of Quantum Dot Sensitized Solar Cells in the Strongly Coupled CdSe Nanocrystals/TiO2 System

Solution processed CuSbS 2 films for solar cell applications

Tailoring Absorber Thickness and the Absorber-Scaffold Interface in CdSe-Coated ZnO Nanowire Extremely Thin Absorber Solar Cells

Ultrafast Charge Carrier Dynamics in Extremely Thin Absorber (ETA) Solar Cells Consisting of CdSe-Coated ZnO Nanowires