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Solar‐driven photoelectrochemical (PEC) reactions using colloidal quantum dots (QDs) as photoabsorbers have shown great potential for the production of clean fuels. However, the low H2 evolution rate, consistent with low values of photocurrent density, and their limited operational stability are still the main obstacles. To address these challenges, the heterostructure engineering of asymmetric capsule‐shaped CdSe/CdxZn1‐xSe QDs with broad absorption and efficient charge extraction compared to pure‐shell QDs is reported. By engineering the shell composition from pure ZnSe shells into CdxZn1‐xSe gradient shells, the electron transfer rate increased from 4.0 × 107 s−1 to 32.7 × 107 s−1. Moreover, the capsule‐shaped architecture enables more efficient spatial carrier separation, yielding a saturated current density of average of 25.4 mA cm−2 under AM 1.5 G one sun illumination. This value is the highest ever observed for QDs‐based devices and comparable to the best‐known Si‐based devices, perovskite‐based devices, and metal oxide‐based devices. Furthermore, PEC devices based on heterostructured QDs maintained 96% of the initial current density after 2 h and 82% after 10 h under continuous illumination, respectively. The results represent a breakthrough in hydrogen production using heterostructured asymmetric QDs. [ABSTRACT FROM AUTHOR]

Recently, significant progress has been made in colloidal quantum dot (QD) based optoelectronic devices for solar energy conversion, such as solar cells, luminescent solar concentrators, and solar-driven photoelectrochemical devices. In this Research Update, we summarized the most recent works on the QD based optoelectronic devices. Particularly, we focused on the effect of the QD structure on the functional properties of QD based devices. The major factors that determine the efficiency of the optoelectronic devices were discussed. In the end, we proposed potential ways to address the future challenges and opportunities of this field. [ABSTRACT FROM AUTHOR]

Semiconductor nanocrystals, the so‐called quantum dots (QDs), exhibit versatile optical and electrical properties. However, QDs possess high density of surface defects/traps due to the high surface‐to‐volume ratio, which act as nonradiative carrier recombination centers within the QDs, thereby deteriorating the overall solar cell performance. The surface passivation of QDs through the growth of an outer shell of different materials/compositions called "core/shell QDs" has proven to be an effective approach to reduce the surface defects and confinement potential, which can enable the broadening of the absorption spectrum, accelerate the carrier transfer, and reduce exciton recombination loss. Here, the recent research developments in the tailoring of the structure of core/shell QDs to tune exciton dynamics so as to improve solar cell performance are summarized. The role of band alignment of core and shell materials, core size, shell thickness/compositions, and interface engineering of core/thick shell called "giant" QDs on electron–hole spatial separation, carrier transport, and confinement potential, before and after grafting on the carrier scavengers (semiconductor/electrolyte), is described. Then, the solar cell performance based on core/shell QDs is introduced. Finally, an outlook for the rational design of core/shell QDs is provided, which can further promote the development of high‐efficiency and stable QD sensitized solar cells. [ABSTRACT FROM AUTHOR]

Modulating the heterostructured interface of semiconductor nanocrystals is being widely explored to enhance the charge transfer rate in photoelectrochemical cells. Here we use electrophoretic deposition and a linker-assisted method to fabricate heterostructured photoanodes based on CdSe quantum dots (QDs) or CdSe(S) nanoplates (NPLs)/TiO2 nanoparticles. The semiconductor nanocrystals exhibit red-shifted or dual photoluminescence emissions after electrophoretic deposition, due to the formation of surface traps. The calculated electron transfer rates in CdSe QDs/TiO2 nanoparticle photoanodes fabricated via electrophoretic deposition and 3-mercaptopropionic acid (MPA)-assisted attachment are 5.5 × 107 s−1 and 2.7 × 107 s−1, respectively, which are both higher than those obtained from NPLs/TiO2 nanoparticles ranging from 0.7 × 107 s−1 to 1.3 × 107 s−1. As a proof of concept, we used heterostructured semiconductor nanocrystals/TiO2 nanoparticles as photoanodes for solar-driven hydrogen generation. Upon one sun illumination, the saturated photocurrent densities of photoanodes fabricated via electrophoretic deposition were found to be higher than those of photoanodes prepared via MPA-assisted attachment, while the corresponding photoanode shows inferior long-term photostability due to the formation of surface traps on the QDs or NPLs during the electrophoretic deposition process. These results provide useful information for engineering the surface/dimension/composition of semiconductor nanocrystals, their adsorption on porous TiO2 films, and designing high-efficiency photoelectrodes in photoelectrochemical devices. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • We demonstrate the first synthesis of ultra-small heavy-metal-free nanoplatelets. • Nanoplatelets exhibit lateral dimension of 6–10 nm with a quantum yield of 20%. • Nanoplatelet-based anode exhibits a saturated photocurrent density of ˜7.4 mA/cm2. • EIS analysis was used to determine the charge transfer resistances. • Nanoplatelets demonstrate potential as light-converter in solar-to-H 2 generation. Abstract Metal chalcogenide semiconducting nanoplatelets exhibit a broad absorption spectrum, as well as thickness-dependent optical and electronic properties. As such, they may be used as building blocks in a variety of optoelectronic devices. The direct synthesis of heavy-metal-free ultra-small sized nanoplatelets is still challenging, due to the inherent limits in existing synthetic approaches. Here, we report an efficient template-assisted cation-exchange route to synthesize heavy metal free metal chalcogenide nanoplatelets that are optically active in the near infrared. The SnSe nanoplatelets, whose lateral dimension is 6–10 nm, exhibit a quantum yield of 20%. The nanoplatelets are applied as light absorbers in a photoelectrochemical (PEC) system for hydrogen generation, leading to a saturated photocurrent density of 7.4 mA/cm2, which is a record for PEC devices using heavy metal-free colloidal quantum dots or nanoplatelets under identical measurement conditions. Our results indicate that quasi-zero-dimensional SnSe nanoplatelets hold great potential as efficient light absorbers for emerging optoelectronic technologies. [ABSTRACT FROM AUTHOR]

Colloidal quantum dots (QDs) are widely studied due to their promising optoelectronic properties. This study explores the application of specially designed and synthesized "giant" core/shell CdSe/(CdS)x QDs with variable CdS shell thickness, while keeping the core size at 1.65 nm, as a highly efficient and stable light harvester for QD sensitized solar cells (QDSCs). The comparative study demonstrates that the photovoltaic performance of QDSCs can be significantly enhanced by optimizing the CdS shell thickness. The highest photoconversion efficiency (PCE) of 3.01% is obtained at optimum CdS shell thickness ≈1.96 nm. To further improve the PCE and fully highlight the effect of core/shell QDs interface engineering, a CdSexS1-x interfacial alloyed layer is introduced between CdSe core and CdS shell. The resulting alloyed CdSe/(CdSexS1-x)5/(CdS)1 core/shell QD-based QDSCs yield a maximum PCE of 6.86%, thanks to favorable stepwise electronic band alignment and improved electron transfer rate with the incorporation of CdSexS1-x interfacial layer with respect to CdSe/(CdS)6 core/shell. In addition, QDSCs based on "giant" core/ CdS-shell or alloyed core/shell QDs exhibit excellent long-term stability with respect to bare CdSe-based QDSCs. The giant core/shell QDs interface engineering methodology offers a new path to improve PCE and the long-term stability of liquid junction QDSCs. [ABSTRACT FROM AUTHOR]

• A triple-layer LSC was fabricated, with an external optical efficiency of 9.1 %, and a PCE of 6.0 %. • The blue-, green- and orange- emitting C-dots have a quantum yield of 90 %, 73 %, and 72 %. • The multilayer LSCs have high CRI above 80 and AVT above 70 %, suitable for efficient BIPVs. Compared to the silicon-based photovoltaics, large-area luminescent solar concentrators (LSCs) can be used as smart PV window for building-integrated photovoltaics (BIPVs). However, because of the low quantum yield of the fluorophores, and reabsorption energy loss, the current obtained large-area LSCs have low optical efficiency. Herein, we demonstrated highly efficient and semitransparent multilayer LSCs based on three types of carbon quantum dots (C-dots). The blue and green C-dots were synthesized using vacuum heating approach and the orange C-dots were synthesized using solvothermal approach. The as-prepared B-, G- and O-C-dots have the QYs of 90 %, 73 % and 72 %, respectively, with large Stokes shift (0.37–0.73 eV). By optimizing the concentration of the C-dots in each layer, the best LSC (100 cm2) with multilayer structure exhibited an external optical efficiency of 9.1 %, and a power conversion efficiency (PCE) of 6.0 %, which are higher than that of most of reported LSCs. The simulations indicate that optimized multilayer LSCs could have a theoretical external optical efficiency over 12 % for 1 m2 devices. Besides high optical efficiency, the multilayer LSCs also have high Color Rendering Index (above 80) and high average visible transmission (above 70 %), which make the as-prepared LSCs suitable for potential commercial BIPVs. [ABSTRACT FROM AUTHOR]

• Eco-friendly CuGaAlS/ZnS core/shell QDs were successfully synthesized. • Optical properties of QDs can be tuned by varying the copper contents. • The optimized QDs show a high PLQY of 91% with a large Stokes-shift. • High-performance and large-area QDs-based LSC device is fabricated. Luminescent solar concentrators (LSCs) fabricated using colloidal quantum dots (QDs) are considered as promising cost-effective solar collectors for future building-integrated photovoltaics (BIPV). Nevertheless, the solar-to-electricity conversion efficiency of the LSCs is commonly low due to limited quantum efficiency and large reabsorption loss of QDs. In addition, most of the efficient LSCs contain heavy metal-based QDs, limiting their potential commercial applications. Herein, we demonstrate a novel type of eco-friendly CuGaAlS/ZnS (CGAS/ZnS) core/shell QDs with efficient surface passivation and manipulated their optical properties by varying the copper contents, which effectively regulates the intrinsic band structure and radiative recombination dynamics. As a result, the optimal Cu-deficient CGAS/ZnS core/shell QDs exhibit the highest photoluminescence quantum yield (PLQY) of ∼ 91 % and large Stokes shift (∼0.81 eV). The prepared QDs were applied as emitters and integrated in polymer matrix to fabricate LSCs (10 × 10 × 0.15 cm3), delivering an unprecedented power conversion efficiency (PCE) of 4.29 % under standard one sun AM 1.5G illumination (100 mW cm−2). Our results imply that tuning the components of multinary environment-friendly core/shell QDs endows the feasibility to realize low-cost and high-efficiency BIPV applications. [ABSTRACT FROM AUTHOR]

Photocurrent density of the spherical CdSe/Cd 0.25 Zn 0.75 Se QDs based photoanode, showing a saturated photocurrent density of 13.5 mA/cm2 and a stable H 2 generation under one sun illumination. [Display omitted] • We report a highly stable photoelectrochemical H 2 evolution based on core/shell QDs. • The hole transfer rate is strongly improved by engineering the band structure of QDs. • The device can maintained 99% of its initial current density after 10 h illumination. Colloidal quantum dots (QDs) are promising photosensitizers for the conversion of solar energy into electric energy or chemical fuels. Particularly, they are potentially used in photoelectrochemical (PEC) devices for the realization of solar-driven hydrogen (H 2) generation because their optoelectronic properties could be tunable by controlling their size/shape/composition. However, the long-term operation stability of the PEC devices based on QDs is not good, which is strongly prohibited the potential of the QDs based PEC hydrogen production. Here, we engineer the band structure of the CdSe QDs via a Zn dopant and demonstrate a highly stable PEC devices based on CdSe/Cd 1-x Zn x Se QDs. Through controlling the molar ratio of Cd/Zn precursors, the Zn concentration in the shell can be finely controlled to form an alloyed shell of Cd 1-x Zn x Se. The alloyed shell enables the efficient hole transfer from the QDs to TiO 2 , benefiting from the optimization of the valence energy alignment between the core and shell. As a proof-of-concept, the PEC device based on alloyed-shell QDs achieves a current density of ∼ 13.5 mA/cm2, which is comparable to the best reported PEC devices. More importantly, the PEC devices maintained 99% of its initial current density after 10 h of continuous H 2 generation under one sun illumination. Even after 50 h operation, the PEC device still keeps 65% of initial current density. The excellent long-term operation stability paves the way for the design and use of doped QDs for potential H 2 production. [ABSTRACT FROM AUTHOR]

• Hybrid ligands exchange replaced ~75% of organic OA ligands. • PEC cells with a hybrid ligand exchange yield two times higher current density. • Hybrid ligand exchange offers reduced charge transfer resistance/prolonged lifetime. Surface ligands facilitate the high dispersibility of colloidal quantum dots (QDs) during synthesis and storage, and also play a key role in passivating surface traps. The most commonly used ligands [oleic acid (OA) or oleylamine (OLA)] are insulating long organic linkers, which prevent efficient charge transfer between QDs and exhibit limited surface passivation, thus significantly reducing the overall performance of QDs based optoelectronic devices. Here we develop a solid-state ligands exchange process for PbS/CdS QDs sensitized TiO 2 photoanode with hybrid inorganic ligands (I− and SCN−) to replace the original insulating OA ligands and passivate the surface traps. The hybrid surface passivation of PbS/CdS QDs removes ~75% of insulating OA ligands. The saturated photocurrent density of the photoelectrochemical (PEC) cells improves significantly through the hybrid ligand exchange process, reaching a value of 4.0 mA cm−2 which is more than two times higher compared to the control PEC cells. In addition, the long-term stability of PEC cells is better for the hybrid ligand exchange process (only 15% loss of its initial photocurrent density) than the control PEC cells (38% loss). Our results indicate that hybrid ligands engineering is a promising pathway to achieve high performance and stable PEC cells for hydrogen generation. [ABSTRACT FROM AUTHOR]