Understanding chemically processed solar cells based on quantum dots

Cognitively Driven Autonomous Flow Chemistry for Producing On-Demand Perovskite Quantum Dots Via Advanced Closed-Loop Feedback Control

Recent developments in the synthesis of hybrid organic-inorganic halide perovskite quantum dots (HP-QDs) through compositional adjustments have highlighted their potential applications in the fields of photovoltaics and light sources due to their unique optoelectronic properties. However, traditional methods to fine-tune their composition involve repetitive, labor-intensive, and costly processes. Herein, the utilization of a continuous flow chemistry approach is developed, in combination with a Proportional-Integral (PI) feedback control system as an effective method for producing on-demand methylammonium lead bromoiodide (MAPbBrx I3-x ) HP-QDs. The PI feedback control allows for real-time optimization of the flow rates of halide precursor solutions (halide PSs), enabling the precise tuning of the emission wavelength of HP-QDs. HP-QDs having an emission wavelength of 550 and 650 nm are synthesized through a blue-shifted and red-shifted algorithm, respectively, from any arbitrary reaction condition within 400 s. The iterative process through the PI feedback control produces the target HP-QDs with short rise time and low overshoot. The proposed automatic flow chemistry system integrated with a universal and accessible control algorithm of PI can generate the target HP-QDs with high accuracy, stability, and robustness, demonstrating a significant advancement in constructing an autonomous flow chemistry synthetic system.

Solar-driven conversion of carbon dioxide over nanostructured metal-based catalysts in alternative approaches: Fundamental mechanisms and recent progress

Solar-driven carbon dioxide (CO₂) conversion has gained tremendous attention as a prominent strategy to simultaneously reduce the atmospheric CO₂ concentration and convert solar energy into solar fuels in the form of chemical bonds. Numerous efforts have been devoted to diverse photo-driven processes for CO₂ conversion, which utilized a multidisciplinary strategy. Among them, the architecture of nanostructured metal-based catalysts is emerging as an eminent solution for the design of catalysts of this field. In this work, we first provide fundamental mechanisms of photochemical, photoelectrochemical, photothermal, and photobio(electro)chemical CO₂ reduction processes to achieve an in-deep understanding of vital aspects. Importantly, the recent progress in the catalyst design for each reaction system is discussed and highlighted. Based on these analyses, an overview of photo-driven CO₂ reduction on metal-based catalysts for solar fuel production is also spotlighted. Finally, we analyze challenges and prospects for the strategic direction of developments in the field.

A polymer-coated template-confinement CsPbBr3 perovskite quantum dot composite

Metal halide perovskites show abundant photophysical properties and great potential in photovoltaic and electroluminescence devices, but their poor stability is an obvious shortcoming. Here, we successfully synthesized polymer-coated CsPbBr₃ quantum dots (QDs) grown in situ on a template. Conjugated linoleic acid (CLA) is used as a ligand to passivate the surface defects of QDs. QDs can be used as photoinitiators in polymerization to initiate CLA crosslinking under illumination, thereby forming polymer coatings to improve the stability of QDs. The mesoporous silica microspheres are used as templates to make CsPbBr₃ QDs grow in situ in the pores and avoid the size growth and agglomeration of QDs. The obtained composite material has a narrow full width at half maximum and an absolute photoluminescence quantum yield of 79.16%. Due to the protection of the hydrophobic polymer layer, it can still maintain 77% of the photoluminescence intensity after soaking in water for a week.

Synthesis of Mn-doped CsPbClxBr3−x perovskite nanocrystals using ultrasonic irradiation-promoted with decrease of reaction order

The incorporation of impurity cation as a way of introducing various novel functionalities provides an additional level of control over the electronic and optical properties of perovskite nanocrystals (NCs). However, the conventional post-synthetic cation exchange approaches suffer from large time and energy consumption. In this work, we developed a novel one-pot method to synthesize Mn-doped CsPbClxBr3−x NCs by merit of sonochemical technique, achieving dramatically rapid reduce of time and energy consumption. The localized hot spots with high transient temperature, pressure, and cooling rate, as well as an excellent stirring action of ultrasonic preparation facilitate the diffusion of Mn2+ in perovskite lattice. Besides, further reaction kinetics investigation reveals an apparent decrease of reaction order from original method (2.4) to our ultrasound-assisted method (1.0).

Improved Reproducibility of PbS Colloidal Quantum Dots Solar Cells Using Atomic Layer-Deposited TiO2

Thanks to their broadly tunable bandgap and strong absorption, colloidal lead chalcogenide quantum dots (QDs) are highly appealing as solution-processable active layers for third-generation solar cells. However, the modest reproducibility of this kind of solar cell is a pertinent issue, which inhibits the exploitation of this material class in optoelectronics. This issue is not necessarily imputable to the active layer but may originate from different constituents of the device structure. Herein, the deposition of TiO2 electron transport layer is focused on. Atomic layer deposition (ALD) greatly improves the reproducibility of PbS QD solar cells compared with the previously optimized sol-gel (SG) approach. Power conversion efficiency (PCE) of the solar cells using atomic layer-deposited TiO2 lies in the range between 5.5% and 7.2%, whereas solar cells with SG TiO2 have PCE ranging from 0.5% to 6.9% with a large portion of short-circuited devices. Investigations of TiO2 layers by atomic force microscopy and scanning electron microscopy reveal that these films have very different surface morphologies. Whereas the TiO2 films prepared by SG synthesis and deposited by spin coating are very smooth, TiO2 films made by ALD repeat the surface texture of the fluorine-doped tin oxide (FTO) substrate underneath.

Recent advances in synthesis and application of perovskite quantum dot based composites for photonics, electronics and sensors

In recent years, halide perovskite quantum dots (HP-QDs) based composites have been widely developed and used in various applications owing to their unique photonic, electronic and mechanical properties, as well as high stability to water, oxygen, heat and illumination. Remarkable efforts have been made in the synthesis and applications of these materials in photonics, electronics, sensors and other fields. Besides these topics, we also cover enhancement of optoelectronic properties as well as chemical, thermal and photostability of HP-QDs-based composites. We hope this review will promote both the development and applications of perovskite-based materials.

Functionalized rGO Interlayers Improve the Fill Factor and Current Density in PbS QDs-Based Solar Cells

Graphene-quantum dot nanocomposites attract significant attention for novel optoelectronic devices, such as ultrafast photodetectors and third-generation solar cells. Combining the remarkable optical properties of quantum dots (QDs) with the exceptional electrical properties of graphene derivatives opens a vast perspective for further growth in solar cell efficiency. Here, we applied (3-mercaptopropyl) trimethoxysilane functionalized reduced graphene oxide (f-rGO) to improve the QDs-based solar cell active layer. The different strategies of f-rGO embedding are explored. When f-rGO interlayers are inserted between PbS QD layers, the solar cells demonstrate a higher current density and a better fill factor. A combined study of the morphological and electrical parameters of the solar cells shows that the improved efficiency is associated with better layer homogeneity, lower trap-state densities, higher charge carrier concentrations, and the blocking of the minor charge carriers.

Quantum Dot Based Solar Cells: Role of Nanoarchitectures, Perovskite Quantum Dots, and Charge-Transporting Layers

Quantum dot solar cells (QDSCs) are attractive technology for commercialization, owing to various advantages, such as cost effectiveness, and require relatively simple device fabrication processes. The properties of semiconductor quantum dots (QDs), such as band gap energy, optical absorption, and carrier transport, can be effectively tuned by modulating their size and shape. Two types of architectures of QDSCs have been developed: 1) photoelectric cells (PECs) fabricated from QDs sensitized on nanostructured TiO₂ , and 2) photovoltaic cells fabricated from a Schottky junction and heterojunction. Different types of semiconductor QDs, such as a secondary, ternary, quaternary, and perovskite semiconductors, are used for the advancement of QDSCs. The major challenge in QDSCs is the presence of defects in QDs, which lead to recombination reactions and thereby limit the overall performance of the device. To tackle this problem, several strategies, such as the implementation of a passivation layer over the QD layer and the preparation of core-shell structures, have been developed. This review covers aspects of QDSCs that are essential to understand for further improvement in this field and their commercialization.

Reversible regulation of CdTe quantum dots fluorescence intensity based on Prussian blue with high anti-fatigue performance

A fluorescence switching device with excellent anti-fatigue performance based on the electrochromic material Prussian blue and fluorophore CdTe quantum dots was realized. The fluorescence switching device ultimately demonstrated a high fluorescence contrast, short response time and superior anti-fatigue property. Notably, the fluorescence contrast remains unchanged after 133 cycles.

Design of 2D-nanocrystals in water: preparation, structure and functionalization

A new method for synthesis of 2D nanocrystals in water was proposed. The use of perfluorothiophenolate ions as surfactant allowed us to produce 2D single-crystal nanosheets of CaS at pH=9 and flat nanocrystals of PbS at pH=9 at room temperature. Mesocrystalline nanobelts of CdS and mesocrystals of PbS were obtained at pH=3–5 and pH=10–12, respectively. Morphology, structure and chemical composition of nanoparticles were characterized by high-resolution transmission electron microscopy, electron diffraction and energy dispersive X-ray spectroscopy. A mechanism of nanoparticles formation was discussed.