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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]

Abstract Colloidal quantum dots (QDs) are semiconductor nanocrystals which exhibit discrete energy levels. They are promising building blocks for optoelectronic devices, thanks to their tunable band structure. Here, we explore a nanoengineering approach to highlight the influence of an alloyed interface on the optical and electronic properties of CdSe/(CdS) 6 "giant" core/shell (CS) QDs by introducing CdSe x S 1-x interfacial layers between core and shell. By incorporating of CdSe x S 1-x interfacial layers, CdSe/(CdSe x S 1-x) 4 /(CdS) 2 (x = 0.5) core/shell (CSA1) QDs exhibit a broader absorption response towards longer wavelength and higher electron-hole transfer rate due to favorable electronic band alignment with respect to CS QDs, as confirmed by optical absorption, photoluminescence (PL) and transient fluorescence spectroscopic measurements. In addition, simulations of spatial probability distributions show that the interface layer enhances electron-hole spatial overlap. As a result, CSA1 QDs sensitized solar cells (QDSCs) yield a maximum photoconversion efficiency (PCE) of 5.52%, which is 79% higher than QDSCs based on reference CS QDs. To fully demonstrate the structural interface engineering approach, the CdSe x S 1-x interfacial layers were further engineered by tailoring the selenium (Se) and sulfur (S) molar ratios during in situ growth of each interfacial layer. This graded alloyed CdSe/(CdSe x S 1-x) 5 /(CdS) 1 (x = 0.9–0.1) core/shell (CSA2) QDs show a further broadening of the absorption spectrum, higher carrier transport rate and modified confinement potential with respect to CSA1 QDs as well as reference CS QDs, yielding a PCE of 7.14%. Our findings define a promising approach to improve the performance of QDSCs and other optoelectronic devices based on CS QDs. Graphical abstract Interfacial engineering of "giant" core/shell (CS) QDs by the incorporation of CdSe x S 1-x interfacial layers as well as tailoring the selenium and sulfur molar ratios during the in-situ growth of each interfacial layer, shows broader absorption, higher electron-hole transfer rate and modified confinement potential with respect to CS QDs, yielding a photoconversion efficiency (PCE) of 7.14%. These findings demonstrate that the interfacial engineering of "giant" CS QDs is a promising approach to improve the performance of energy conversion devices based on QDs. fx1 Highlights • Interfacial engineering of QDs builds a favorable stepwise electronic band alignment. • The graded alloyed QDs exhibit a broad absorption response toward a longer wavelength. • The incorporation of engineered interfacial layers enhances the electron-hole transfer rate. • QDSC based on graded alloyed QDs yields a maximum PCE of 7.14%. [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]

All solution processed depleted bulk heterojunction (DBH) solar cell devices based on near infrared (NIR) PbS/CdS core–shell quantum dots (QDs) and films of rutile TiO2 nanorod arrays have been investigated. The device fabrication was achieved through the layer-by-layer spin coating of PbS/CdS QDs, in ambient atmosphere, onto hydrothermally grown TiO2 nanorod arrays film leading to the general device architecture consisting of fluorine doped tin oxide (FTO)/TiO2/QDs/interfacial layer/Au. The performance of these devices fabricated under different processing conditions was tested and compared with that of similar devices where the PbS/CdS QDs were replaced by a spin-coated layer of colloidal PbS QDs (processed under inert atmosphere). It was found that the maximum power conversion efficiency of the former devices is about 40% higher when MoO3 was used as an interfacial layer (2.02%±0.15 vs 1.40%±0.11). The stability and ease of processing in air together with the higher performance of the PbS/CdS core–shell QDs, as compared to the PbS QDs, strongly suggest their high potential in solar cell applications. This work represents the first demonstration of the use of NIR PbS/CdS core–shell QDs in solar cells. [ABSTRACT FROM AUTHOR]

Quantum Dots Solar Cells: Core/Shell Quantum Dots Solar Cells (Adv. Funct. Keywords: carrier dynamics; core/shell quantum dots; interface engineering; quantum dot sensitized solar cells EN carrier dynamics core/shell quantum dots interface engineering quantum dot sensitized solar cells 1 1 1 03/28/20 20200324 NES 200324 In article number 1908762, Haiguang Zhao, Zhiming M. Wang, Federico Rosei, and Gurpreet Singh Selopal report on colloidal core/shell quantum dots (QDs) that exhibit promising optical and electrical properties. Carrier dynamics, core/shell quantum dots, interface engineering, quantum dot sensitized solar cells. [Extracted from the article]

We report the effect of incorporating different loadings of graphene nanoribbons (GNR) into a standard photoanode made of TiO 2 sensitized with dye molecules. The GNRs are observed to significantly improve the photoconversion efficiency (PCE) of dye-sensitized solar cells (DSSCs). The TiO 2 -GNR hybrid photoanodes were prepared using the doctor-blade method. The presence of GNR in the composite photoanode was characterized by scanning electron microscopy, transmission electron microscopy and Raman spectroscopy. Our results highlight that, at an optimum loading of 0.005 wt%, GNR increases the PCE of DSSCs up to values 20% higher than the PCE of control devices. This improvement is mainly attributed to improved dye loading, enhanced electron lifetime and reduced carrier recombination, as confirmed by quantitative measurements of dye loading, transient photovoltage decay and electrochemical impedance spectroscopy results, respectively. [ABSTRACT FROM AUTHOR]

The counter electrode (CE) plays a significant role in determining the overall performance and long-term stability of quantum dots (QDs) sensitized solar cells (QDSCs) by collecting the electrons from the external circuit and catalyzing the regeneration of the oxidized electrolyte. In this work, we report a simple, low cost and large area scalable spray deposition approach to fabricate nanostructured Cu 2 S CE on a carbon fiber paper (CP). The QDSCs were assembled with optimized spray assisted nanostructured Cu 2 S/CP CEs, and yield a photoconversion efficiency (PCE) of 5.06%, which is 28% higher than QDSCs based on Cu 2 S/Brass CEs. The PCE can be further boosted to 5.89% upon optimization of the photoanode structure. In addition, QDSCs with Cu 2 S/CP CEs exhibit better long-term stability than QDSCs with Cu 2 S/Brass CE. This excellent performance and satisfactory long-term stability of QDSCs with Cu 2 S/CP CEs is mainly attributed to the synergistic effect of excellent conductivity of CP and high and stable catalytic activity of nanostructured Cu 2 S, which is confirmed by cyclic voltammetry and electrochemical impedance spectroscopy. Thus, our results define a cost-effective and large area scalable approach to fabricate highly efficient and stable CEs, which is an important step toward the fabrication of solar driven optoelectronic devices. Image 1 • The spray deposition approach was used to fabricate efficient and stable Cu 2 S/CP CE. • Cu 2 S/CP CEs offer low series resistance and high catalytic activity. • QDSC based on Cu 2 S/CP CEs yield a 28% higher PCE than the brass CEs. • A PCE of 5.89% can be obtained upon the optimization of the photoanode structure. [ABSTRACT FROM AUTHOR]