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The manipulation of the dimensionality and nanostructures based on the precise control of the crystal growth kinetics boosts the flourishing development of perovskite optoelectronic materials and devices. Herein, a low-dimensional inorganic tin halide perovskite, CsSnBrI2-x (SCN)x , with a mixed 2D and 3D structure is fabricated. A kinetic study indicates that Sn(SCN)2 and phenylethylamine hydroiodate can form a 2D perovskite structure that acts as a template for the growth of the 3D perovskite CsSnBrI2-x (SCN)x . The film shows an out-of-plane orientation and a large grain size, giving rise to reduced defect density, superior thermostability, and oxidation resistance. A solar cell based on this low-dimensional film reaches a power conversion efficiency of 5.01 %, which is the highest value for CsSnBrx I3-x perovskite solar cells. Furthermore, the device shows enhanced stability in ambient air.

Narrow-bandgap tin-lead (Sn-Pb) mixed perovskite solar cells (PSCs) play a key role in constructing perovskite tandem solar cells that are potential to overpass Shockley-Queisser limit. A robust, chemically stable and low-temperature-processed hole transporting layer (HTL) is essential for building high-efficiency Sn-Pb solar cells and perovskite tandem solar cells. Here, we explore a room-temperature-processed NiO x (L-NiO x ) HTL based on nanocrystals (NCs) for Sn-Pb PSCs. In comparison with high-temperature-annealed NiO x (H-NiO x ) film, the L-NiO x film shows deeper valence band and lower trap density, which increases the built-in potential and reduces carrier recombination, leading to a power conversion efficiency of 18.77%, the record for NiO x -based narrow-bandgap PSCs. Furthermore, the device maintains about 96% of its original efficiency after 50 days. This work provides a robust and room-temperature-processed HTL for highly efficient and stable narrow-bandgap PSCs.

Summary With rapid progress in perovskite light-emitting diodes (PeLEDs), the electroluminescence performance of large-area is of increasing interest. We investigated why large-area performance lags behind that achieved in laboratory-scale devices and found that defects in perovskite films—emerging from thermal convection during solvent evaporation, as well as electronic traps formed during perovskite crystallization—are chief causes. Here, we report a molecular modification strategy that simultaneously eliminates pinholes in perovskite layers by controlling the dynamics of film formation and that passivates defects in perovskites by incorporating Br species, thereby preventing shorts and non-radiative recombination. The molecular modifier 1,3,5-tris (bromomethyl) benzene (TBB) also modulates the electronic structure of injection or transport materials to achieve improved charge injection and balanced charge transport. As a result, we demonstrate 20 mm × 20 mm green perovskite nanocrystal LEDs that achieve an external quantum efficiency (EQE) of over 16%, a record for large-area PeLEDs.

The insertion of large organic cations in metal halide perovskites with reduced-dimensional (RD) crystal structures increases crystal formation energy and regulates the growth orientation of the inorganic domains. However, the power conversion performance is curtailed by the insulating nature of the bulky cations. Now a series of RD perovskites with 2-thiophenmethylammonium (TMA) as the intercalating cation are investigated. Compared with traditional ligands, TMA demonstrates improved electron transfer in the inorganic framework. TMA modifies the near-band-edge integrity of the RD perovskite, improving hole transport. A power conversion efficiency of 19 % is achieved, the highest to date for TMA-based RD perovskite photovoltaics; these TMA devices provide a 12 % relative increase in PCE compared to control RD perovskite devices that use PEA as the intercalating ligand, a result of the improved charge transfer from the inorganic layer to the organic ligands.

Tin perovskite is rising as a promising candidate to address the toxicity and theoretical efficiency limitation of lead perovskite. However, the voltage and efficiency of tin perovskite solar cells are much lower than lead counterparts. Herein, indene-C60 bisadduct with higher energy level is utilized as an electron transporting material for tin perovskite solar cells. It suppresses carrier concentration increase caused by remote doping, which significantly reduces interface carriers recombination. Moreover, indene-C60 bisadduct increases the maximum attainable photovoltage of the device. As a result, the use of indene-C60 bisadduct brings unprecedentedly high voltage of 0.94 V, which is over 50% higher than that of 0.6 V for device based on [6,6]-phenyl-C61-butyric acid methyl ester. The device shows a record power conversion efficiency of 12.4% reproduced in an accredited independent photovoltaic testing lab., Despite the lower device efficiency, tin perovskite based solar cells are preferred choices compared to lead-based counterparts due to much lower toxicity. Here Jiang et al. use a fullerene derivative to greatly suppress carrier interface recombination and obtain record high cell efficiency of 12%.

Lead halide perovskites with mixed cations/anions often suffer from phase segregation, which is detrimental to device efficiency and their long-term stability. During perovskite film growth, the gel stage (in between liquid and crystalline) correlates to phase segregation, which has been rarely explored. Herein, cation diffusion kinetics are systematically investigated at the gel stage to develop a diffusion model obeying Fick's second law. Taking 2D layered perovskite as an example, theoretical and experimental results reveal the impact of diffusion coefficient, temperature, and gel duration on the film growth and phase formation. A homogenous 2D perovskite thin film was then fabricated without significant phase segregation. This in-depth understanding of gel stage and relevant cation diffusion kinetics would further guide the design and processing of halide perovskites with mixed composition to meet requirements for optoelectronic applications.

All-inorganic metal halide perovskites are noted for their excellent optoelectronic properties and good chemical stability but also a propensity to transform into nonperovskite phases. A case in po...

With efficiency of perovskite solar cells (PSCs) overpassing 23%, to realize their commercialization, the biggest challenge now is to boost the stability to the same level as conventional solar cells. Thus, tremendous effort has been directed over the past few years toward improving the stability of these cells. Various methods were used to improve the stability of bulk perovskites, including compositional engineering, interface adjustment, dimensional manipulation, crystal engineering, and grain boundary decoration. Diverse device configurations, carrier transporting layers, and counter electrodes are investigated. To compare the stability of PSCs and clarify the degradation mechanism, diverse characterization methods were developed. Overall stability of PSCs has become one central topic for the development of PSCs. In this review, we summarize the state-of-the-art progress on the improvement of device stability and discuss the directions for future research, hoping it provides an overview of the current status of the research on the stability of PSCs and guidelines for future research.

Highlights Recent progress of efficiency and long-term stability for perovskite solar cells, and the development of perovskite-based tandem solar cells are described. The progress of lead-free perovskite solar cells and their potential for industrial production are discussed in detail. The current status, ongoing challenges, and the future outlooks of perovskite solar cells are highlighted., Perovskite solar cells (PSCs) emerging as a promising photovoltaic technology with high efficiency and low manufacturing cost have attracted the attention from all over the world. Both the efficiency and stability of PSCs have increased steadily in recent years, and the research on reducing lead leakage and developing eco-friendly lead-free perovskites pushes forward the commercialization of PSCs step by step. This review summarizes the main progress of PSCs in 2020 and 2021 from the aspects of efficiency, stability, perovskite-based tandem devices, and lead-free PSCs. Moreover, a brief discussion on the development of PSC modules and its challenges toward practical application is provided.

The optical responses of molecules and materials provide a basis for chemical measurement and imaging. The optical diffraction limit in conventional light microscopy is exceeded by mechanically probing optical absorption through the photothermal effect with atomic force microscopy (AFM). However, the spatial resolution of AFM-based photothermal optical microscopy is still limited, and the sample surface is prone to damage from scratching due to tip contact, particularly for measurements on soft matter. In this article, we develop peak force visible (PF-vis) microscopy for the measurement of visible optical absorption of soft matter. The spatial resolution of PF-vis microscopy is demonstrated to be 3 nm on green fluorescent protein-labeled virus-like particles, and the imaging sensitivity may approach a single protein molecule. On organic photovoltaic polymers, the spatial distribution of the optical absorption probed by PF-vis microscopy is found to be dependent on the diffusion ranges of excitons in the donor domain. Through finite element modeling and data analysis, the exciton diffusion range of organic photovoltaics can be directly extracted from PF-vis images, saving the need for complex and delicate sample preparations. PF-vis microscopy will enable high-resolution nano-imaging based on light absorption of fluorophores and chromophores, as well as deciphering the correlation between the spatial distribution of photothermal signals and underlying photophysical parameters at the tens of nanometer scale.

Colloidal quantum dots (CQDs) are emerging as promising materials for the next generation infrared (IR) photodetectors, due to their easy solution processing, low cost manufacturing, size-tunable optoelectronic properties, and flexibility. Tremendous efforts including material engineering and device structure manipulation have been made to improve the performance of the photodetectors based on CQDs. In recent years, benefiting from the facial integration with materials such as 2D structure, perovskite and silicon, as well as device engineering, the performance of CQD IR photodetectors have been developing rapidly. On the other hand, to prompt the application of CQD IR photodetectors, scalable device structures that are compatible with commercial systems are developed. Herein, recent advances of CQD based IR photodetectors are summarized, especially material integration, device engineering, and scalable device structures.

The insertion of large organic cations in metal halide perovskites with reduced-dimensional (RD) crystal structures increases crystal formation energy and regulates the growth orientation of the inorganic domains. However, the power conversion performance is curtailed by the insulating nature of the bulky cations. Now a series of RD perovskites with 2-thiophenmethylammonium (TMA) as the intercalating cation are investigated. Compared with traditional ligands, TMA demonstrates improved electron transfer in the inorganic framework. TMA modifies the near-band-edge integrity of the RD perovskite, improving hole transport. A power conversion efficiency of 19 % is achieved, the highest to date for TMA-based RD perovskite photovoltaics; these TMA devices provide a 12 % relative increase in PCE compared to control RD perovskite devices that use PEA as the intercalating ligand, a result of the improved charge transfer from the inorganic layer to the organic ligands.

The power conversion efficiency (PCE) of tin perovskite solar cells is impeded by the extremely poor resistance to oxidation and high density of intrinsic Sn vacancies. Herein, we grow a 2D-quasi-2D-3D Sn perovskite film using removable pseudohalogen NH4SCN as a structure regulator. This hierarchy structure remarkably enhances air stability resulting from the parallel growth of 2D PEA(2)SnI(4) as the surface layer. We then explore the hierarchy structure perovskite films in planar structural solar cells, which generate a PCE up to 9.41%. The device retains 90% of its initial performance for almost 600 hr. Our results suggest that adding removable NH4SCN in a perovskite precursor can significantly improve the stability and photovoltaic performance of Sn perovskite. This finding provides a powerful strategy to manipulate the structure of low-dimensional perovskite in order to enhance the performance of perovskite solar cells.

We show that the performance of single-walled carbon nanotubes (SWCNTs) based infrared photodetector can be greatly enhanced through the combination with colloidal PbS quantum dots (QDs). To improve the photo-induced charge transport efficiency and the carrier mobility, the colloidal PbS QDs are modified by short-chain inorganic. Under illumination, the light-induced electron-hole pairs can be effectively separated by the internal electric field formed at the interfaces between SWCNTS and PbS QDs, which will lead to the increase of both conductivities in them. Photocurrent is formed under the driving of source-drain voltage ( V ds) applied by the interdigital finger electrodes. Our hybrid phototransistor achieves a responsivity of 7.2 A/W, a specific detectivity (defined below) of 7.1×1010 Jones, and a response time of 1.58 ms at the same time under 1550-nm illumination with low intensity. Through gate voltage tuning, the responsivity can be increased to 353.4 A/W. In addition, our hybrid phototransistor is stable, low-cost, and compatible with complementary metal oxide semiconductor, which benefits a lot in real applications.

Recently, layered perovskites attracted great attention for its excellent stability and light-emitting property. However, most of them rely on the toxic element lead and their emission quantum yields are generally low. Here, a unique hollow two-dimensional perovskite was developed in which the organic hexamethylene diamines (C6H18N22+) strongly coupled with distorted tin bromide anions (SnBr64-). This toxic-free low-dimensional tin perovskite exhibits a broadband emission in the visible region with a high luminescence quantum yield of 86%. First-principles calculation indicate the broadband emission is associated with the recombination of self-trapped excitons. And the emission is related to the geometry of tin bromide anions. An ultraviolet light-pumped white light emitting diode with excellent color-rendering index of 94 was fabricated using it together with a commercially available blue phosphor.

Controlling the nucleation and growth of organic-inorganic hybrids perovskite is of key importance to improve the morphology and crystallinity of perovskite films. However, the growth mechanism of perovskite films based on classical crystallization theory is not fully understood. Here, we develop a supersaturation controlled strategy (SCS) to balance the nucleation and crystal growth speeds. By this strategy, we are able to find an ideal supersaturation region to realize a balance of nucleation and crystal growth, which yields highly crystallized perovskite films with micrometer-scale grains. Besides, we provide a thoughtful analysis of nucleation and growth based on the fabrication of the perovskite films. As a result, the highest photovoltaic power conversion efficiencies (PCE) of 19.70% and 20.31% are obtained for the planar and the meso-superstructured devices, respectively. This strategy sheds some light for understanding the film growth mechanism of high quality perovskite film, and it provides a facile strategy to fabricate high efficiency perovskite solar cells.

The stability of perovskite is a bottleneck for the application of perovskite solar cells. Herein, 4-ethylamine Phenylphosphate disodium salt (EAPP) was explored as a functional surface ligand to passivate perovskite surface. As the addition of 1 mol% of EAPP, the degradation of the film in high humidity condition was effectively reduced. Solar cells based on EAPP doped perovskite film show merely slight decrease of its initial efficiency in high humidity condition, whereas the control device show catastrophic decrease. Apart from as a passivating molecule to protect perovskite from contacting with water, EAPP show function as a reducing reagent to bond with hydrogen iodide formed in perovskite decomposition.

The development of photocatalysts that can effectively harvest visible light is essential for advances in high-efficiency solar-driven hydrogen generation. Herein, we synthesized water soluble CuInS2 (CIS) and Cu-In-Zn-S (CIZS) quantum dots (QDs) by using one-pot aqueous method. The CIZS QDs are well passivated by glutathione ligands and are highly stable in aqueous conditions. We subsequently applied these QDs as a light harvesting material for photocatalytic hydrogen generation. Unlike most small band gap materials that show extremely low efficiency, these new QDs display remarkable energy conversion efficiency in the visible and near-infrared regions. The external quantum efficiency at 650 nm is ∼1.5%, which, to the best of our knowledge, is the highest value achieved until now in the near-infrared region.

Hydrogen generation based on photocatalytic water splitting is a promising strategy for renewable energy production. Significant efforts have been made to improve the photocatalytic efficiency. However, the light harvesting ability of photocatalytic systems in the visible region still needs to be significantly improved to enable them to be a competitive technology for hydrogen generation. Herein, for the first time, we synthesized 2D Zn–Ag–In–S (ZAIS) nanosheets with strong absorption in the visible region and applied them for photocatalytic hydrogen generation. The exploration of oxygen passivation (O-ZAIS) reduced the defect concentration and nonradiative decay. The hydrogen generation rate is up to 25.2 mmol g−1 h−1, which is 14.7 times higher than that of pristine ZAIS nanosheets. Furthermore, by introducing 2D Co3O4 as the co-catalyst, carrier separation is accelerated, giving rise to a hydrogen generation efficiency of 43.6 mmol g−1 h−1. To the best of our knowledge, this is the highest efficiency reported among all kinds of 2D photocatalysts.

Advancement of electrocatalysts relies on the construction of both a highly efficient catalytic center and a highly conductive network support. Herein, we prepared a 3D interwoven structure with Pd atoms deposited on homogeneously bound MnO2 nanowires and carbon nanotubes (CNTs) (Pd/MnO2–CNT), allowing the combination of superior catalytic performance of atomic Pd incorporated in the metal oxide and the high conductivity of CNT. Using this nanocomposite, stable bifunctional oxygen reduction/evolution reaction (ORR/OER) was achieved. Pd/MnO2–CNT displayed a large Pd mass activity for ORR, which is two magnitudes higher than that of Pd/CNT and 5-fold higher than that of the state-of-the-art Pd-based electrocatalysts operated in alkaline medium. Application of this composite catalyst in Zn–air batteries generates significantly high efficiency and cycling stability. Experimental and theoretical studies revealed that MnO2 provided stronger electronic metal–support interaction than CNT. Pd single atoms doped in MnO2 work synergistically with the surrounding metal sites to activate molecular oxygen, and display optimized binding strength to reaction intermediates. Our strategy can be generalized to design new single atom electrocatalysts for numerous functionalities.

Although halide perovskite nanocrystals (NCs) are promising materials for optoelectronic devices, they suffer severely from chemical and phase instabilities. Moreover, the common capping ligands like oleic acid and oleylamine that encapsulate the NCs will form an insulating layer, precluding their utility in optoelectronic devices. To overcome these limitations, we develop a postsynthesis passivation process for CsPbI3 NCs by using a bidentate ligand, namely 2,2′-iminodibenzoic acid. Our passivated NCs exhibit narrow red photoluminescence with exceptional quantum yield (close to unity) and substantially improved stability. The passivated NCs enabled us to realize red light-emitting diodes (LEDs) with 5.02% external quantum efficiency and 748 cd/m2 luminance, surpassing by far LEDs made from the nonpassivated NCs.

Mixed lead-tin (Pb-Sn) perovskites present a promising strategy to extend the light-harvesting range of perovskite-based solar cells (PSCs). The use of electrontransporting layer or hole-transporting layer (HTL) is critical to achieve high device efficiency. This strategy, however, requires tedious layer-by-layer fabrication as well as high-temperature annealing for certain oxides. In this work, we fabricated HTL-free planar FAPb0.5Sn0.5I3 PSCs with the highest efficiency of 7.94%. High shortcircuit current density of 23.13 mA/cm2 was attained, indicating effective charge extraction at the ITO/FAPb0.5Sn0.5I3 interface. This finding provides an alternative strategy to simplify the manufacture of single-junction or tandem PSCs.

Halide perovskites have emerged as superstar materials for optoelectronic devices. Besides the fever of research in solar cells, these materials show great promise on light emitting diodes (LEDs), photodetectors and lasers as well. Rapid advances in bulk perovskite materials aroused universal interest for the development of perovskite nanocrystals, inspired by the great progress of classic colloidal semiconductor quantum dots. Perovskite nanocrystals have been synthesized based on solution process and exhibited high luminescence quantum yield, sharp emission peak, and emission color tunability. Significant progresses have been made about the application of perovskite nanocrystals for LED and lasers in recent years. In this paper, we will comprehensively introduce the synthesis strategies, physical and chemical characteristics, as well as their applications in optoelectronic devices.

The Dion-Jacobson quasi-2D structure improves the stability of perovskite light-emitting diodes., Organic-inorganic hybrid halide perovskites are emerging as promising materials for next-generation light-emitting diodes (LEDs). However, the poor stability of these materials has been the main obstacle challenging their application. Here, we performed first-principles calculations, revealing that the molecule dissociation energy of Dion-Jacobson (DJ) structure using 1,4-bis(aminomethyl)benzene molecules as bridging ligands is two times higher than the typical Ruddlesden-Popper (RP) structure based on phenylethylammonium ligands. Accordingly, LEDs based on the DJ structure show a half-lifetime over 100 hours, which is almost two orders of magnitude longer compared with those based on RP structural quasi–two-dimensional perovskite. To the best of our knowledge, this is the longest lifetime reported for all organic-inorganic hybrid perovskites operating at the current density, giving the highest external quantum efficiency (EQE) value. In situ tracking of the film composition in operation indicates that the DJ structure was maintained well after continuous operation under an electric field.

Arsenic trioxide (As2O3) is widely used in traditional Chinese medicine to treat tumors. This study investigated the effect of As(III) on pyroptosis in murine hepatocytes in vitro and how this relates to autophagy. NCTC1469-cells were treated with As(III) alone (6, 12 and 18 μM) or in combination with N-acetylcysteine (NAC,1 mM), 3-methyladenine (3-MA, 5 mM) or rapamycin (Rapa,100 nM) for 24 h. The results showed that As(III)-treatment reduced cell viability in a dose-dependent manner, but induced lactic dehydrogenase (LDH) activity. As(III)-treatment also resulted in increased intracellular reactive oxygen species (ROS) levels and decreased mitochondrial membrane potential (MMP), therefore promoting pyroptosis. Moreover, As(III)-treatment upregulated the expression of autophagy and pyroptosis-related genes (LC3-A, LC3-B, P62, Beclin-1, Atg5, Caspase-1, Gasdermin D, IL-18, IL-1β) and downregulated the expression of m-TOR, NLRP3, ASC genes. Meanwhile the accumulation of light chain 3-B/A (LC3B/LC3A), autophagy-related gene 5 (Atg-5), Bcl-2-interacting protein (Beclin-1), Caspase-1, Gasdermin D, interleukin-1β (IL-1β), IL-18 and poptosis-associated speck-like protein (ASC) proteins were upregulated while nucleotide binding and oligomerization domain-like receptor family pyrin domain-containing 3 (NLRP3) was downregulated in all As(III)-treatment groups. Furthermore, the inhibition of autophagy by 3-MA aggravated AsIII-induced pyroptosis and cytotoxicity. However, NAC or Rapa markedly alleviated the abovementioned phenomenon under As(III) stress. In addition, we speculate that the protective mechanism of NAC on As(III)-induced pyroptosis in hepatocytes mainly include the elimination of ROS because of the chelation of As(III) in the culture medium. In conclusion, these results provide new insight into the mechanisms underlying AsIII-induced cytotoxicity and pyroptosis in hepatocytes in vitro.

The application of colloidal quantum dots for light-emitting devices has attracted considerable attention in recent years, due to their unique optical properties such as size-dependent emission wavelength, sharp emission peak and high luminescent quantum yield. Tremendous efforts have been made to explore quantum dots for light-emission applications such as light-emitting diodes (LEDs) and light converters. The performance of quantum-dots-based light-emitting diodes (QD-LEDs) has been increasing rapidly in recent decades as the development of quantum-dots synthesis, surface-ligand engineering and device-architecture optimization. Recently, the external quantum efficiencies of red quantum-dots LEDs have exceeded 20.5% with good stability and narrow emission peak. In this review, we summarize the recent advances in QD-LEDs, focusing on quantum-dot surface engineering and device-architecture optimization.

The structure of the perovskite solar cells (PSCs) is either mesoporous or planar. Here, a novel structure for highly efficient and stable PSCs is proposed, i.e., an embedded structure, which combines the advantages of the mesoporous and planar structures. The embedded structure utilizes a TiO2 nanoparticle embedded perovskite (CH3NH3PbI3) film as the absorption layer. The presence of TiO2 nanoparticles in the perovskite film could improve the electron extraction, and promote the formation of a compact perovskite layer with large grains. Consequently, the performance of the PSCs is significantly improved with the efficiency increasing from 16.6% for the planar structure to 19.2% for the embedded structure, which is the best performance of the MAPbI3-based PSCs. Furthermore, the TiO2 embedded perovskite films present better long-term stability than the pristine perovskite films, and the corresponding PSCs, which have no other chemical modifications, also show excellent stability with efficiency approaching 80% (for average) or 90% (for the best) after being exposed to air for 28 days without encapsulation.

Perovskites with the multi-cation composition of cesium (Cs), methylammonium (MA), and formamidinium (FA) (CsMAFA) are pursued for their high power conversion efficiencies, but they are limited by their thermal stability. To withstand damp-heat accelerated aging MA-free compositions such as CsFA are of interest, but these exhibit lower carrier diffusion lengths and thus lesser performance in photovoltaic devices. A band engineering strategy that overcomes limited carrier diffusion within inverted perovskite solar cells based on CsFA is reported. A joint experimental-computational study shows that treating the perovskite with an n-type molecular dopant increases band bending, shaping the electric field across the active layer to overcome limited diffusive transport. Using this strategy, CsFA solar cell devices with stabilized power conversion efficiencies of 20.3%, a high value for devices using CsFA active layers, are fabricated.

Perovskite solar cells (PSCs) have excellent photovoltaic properties. There are, however, challenges of materials cost and device stability to be solved before commercializing them. Utilizing low-cost inorganic hole transport materials (HTM) as a replacement for spiro-OMeTAD, and replacing the Au electrode with printable carbon could be important steps in this regard. For this purpose, CuInxGa1-xS2 (x = 1, 0.75, 0.5, 0.25, 0) nanoparticle layers are deposited as inorganic HTMs with carbon composite electrode as the back electrode. Photovoltaic properties of PSCs with CuInxGa1-xS2/Carbon hole collecting electrodes are studied by changing the In ratio in the HTM layer. Results from impedance spectroscopy show that by decreasing x value the charge transfer resistance at the interface of hole collector and perovskite layer decrease which matches the downward trend of fill factor of the corresponding cells. The efficiency of PSCs increases during the first week, while, on average, their efficiency drop after one month is less than 5% of the initial values. The best efficiency of 16.45% has been obtained for CuIn0.75Ga0.25S2/carbon hole collectors.

Embedding quantum dots in a perovskite matrix yields efficient light emitters. Colloidal quantum dots (CQDs) are emerging as promising materials for constructing infrared sources in view of their tunable luminescence, high quantum efficiency and compatibility with solution processing1. However, CQD films available today suffer from a compromise between luminescence efficiency and charge transport, and this leads to unacceptably high power consumption. Here, we overcome this issue by embedding CQDs in a high-mobility hybrid perovskite matrix. The new composite enhances radiative recombination in the dots by preventing transport-assisted trapping losses; yet does so without increasing the turn-on voltage. Through compositional engineering of the mixed halide matrix, we achieve a record electroluminescence power conversion efficiency of 4.9%. This surpasses the performance of previously reported CQD near-infrared devices two-fold, indicating great potential for this hybrid QD-in-perovskite approach.

We demonstrate the electron transfer between gold nanoparticles and perovskite CH3NH3PbI3 at a single nanoparticle level by plasmon resonance Rayleigh scattering spectroscopy. Different mass concentrations of CH3NH3PbI3 show different formations of crystal grains on the gold nanoparticles, which led to different degrees of red-shift.

Colloidal quantum dots (CQDs) are fast-improving materials for next-generation solution-processed optoelectronic devices such as solar cells, photocatalysis, light emitting diodes, and photodetectors. Nanoscale CQDs exhibit a high surface to volume ratio, and a significant fraction of atoms making up the quantum dots are thus located on the surface. CQD surface states therefore play a critical role in determining these materials' properties, influencing luminescence, defect energy levels, and doping type and density. In the past five years, halide ligands were applied to CQD solar cells, and these not only improved charge carrier mobility, but also reduced defects on the surface. With the inclusion of halide ligands, CQD solar cell certified power conversion efficiencies have increased rapidly from an initial 5% in 2010 to the latest certified values over 10%. In this perspective article, we summarize recent advances in ligand engineering that improve the performance of CQD solar cells, focusing on the use of halide inorganic ligands to improve CQD surface passivation and film conductivity simultaneously.

Highly efficient PbS colloidal quantum dot (QD) solar cells based on an inverted structure have been missing for a long time. The bottlenecks are the construction of an effective p-n heterojunction at the illumination side with smooth band alignment and the absence of serious interface carrier recombination. Here, solution-processed nickel oxide (NiO) as the p-type layer and lead sulfide (PbS) QDs with iodide ligand as the n-type layer are explored to build a p-n heterojunction at the illumination side. The large depletion region in the QD layer at the illumination side leads to high photocurrent. Interface carrier recombination at the interface is effectively prohibited by inserting a layer of slightly doped p-type QDs with 1,2-ethanedithiol as ligands, leading to improved voltage of the device. Based on this graded device structure design, the efficiency of inverted structural heterojunction PbS QD solar cells is improved to 9.7%, one time higher than the highest efficiency achieved before.

Organolead halide perovskites have emerged as potential building blocks for photovoltaic and optoelectronic devices. Yet the underlying fundamental physics is not well understood. There is lack of agreement on the electronic band structures and binding energies of coupled electron-hole pairs (excitons), which drive the photophysical processes. In this work, we conducted temperature-dependent reflectance and photoluminescence experiments on high-quality ${\mathrm{CH}}_{3}{\mathrm{NH}}_{3}{\mathrm{PbBr}}_{3}$ single crystals. Two direct optical transitions corresponding to intrinsic free-excitons are clearly resolved, showing excellent consistence between the low-temperature ($T=10$ K) reflectance and photoluminescence spectra. Remarkably, the excitons have different binding energies and behave oppositely with temperature, suggesting distinctive origins. Moreover, the asymmetric photoluminescence profile is counterintuitively dominated by the high-energy exciton that is explained by a long relaxation time between levels and by the favorable generation rate of electron-hole pairs at the high-energy band. Our study opens access to the intrinsic properties of ${\mathrm{CH}}_{3}{\mathrm{NH}}_{3}{\mathrm{PbBr}}_{3}$ and sheds light to reconcile the large range of binding energies reported on these emergent direct band-gap semiconductors.

Because of the rapid rise of the efficiency, perovskite solar cells are currently considered as the most promising next-generation photovoltaic technology. Much effort has been made to improve the efficiency and stability of perovskite solar cells. Here, it is demonstrated that the addition of a novel organic cation of 2-(6-bromo-1,3-dioxo-1H-benzo[de]isoquinolin-2(3H)-yl)ethan-1-ammonium iodide (2-NAM), which has strong Lewis acid and base interaction (between C=O and Pb) with perovskite, can effectively increase crystalline grain size and reduce charge carrier recombination of the double cation FA(0.83)MA(0.17)PbI(2.51)Br(0.49) perovskite film, thus boosting the efficiency from 17.1 +/- 0.8% to 18.6 +/- 0.9% for the 0.1 cm(2) cell and from 15.5 +/- 0.5% to 16.5 +/- 0.6% for the 1.0 cm(2) cell. The champion cell shows efficiencies of 20.0% and 17.6% with active areas of 0.1 and 1.0 cm(2), respectively. Moreover, the hysteresis behavior is suppressed and the stability is improved. The result provides a promising route to further elevate efficiency and stability of perovskite solar cells by the fine tuning of triple organic cations.

The low toxicity and a near-ideal choice of bandgap make tin perovskite an attractive alternative to lead perovskite in low cost solar cells. However, the development of Sn perovskite solar cells has been impeded by their extremely poor stability when exposed to oxygen. We report low-dimensional Sn perovskites that exhibit markedly enhanced air stability in comparison with their 3D counterparts. The reduced degradation under air exposure is attributed to the improved thermodynamic stability after dimensional reduction, the encapsulating organic ligands, and the compact perovskite film preventing oxygen ingress. We then explore these highly oriented low-dimensional Sn perovskite films in solar cells. The perpendicular growth of the perovskite domains between electrodes allows efficient charge carrier transport, leading to power conversion efficiencies of 5.94% without the requirement of further device structure engineering. We tracked the performance of unencapsulated devices over 100 h and found no appreciable decay in efficiency. These findings raise the prospects of pure Sn perovskites for solar cells application.

Large-bandgap perovskites offer a route to improve the efficiency of energy capture in photovoltaics when employed in the front cell of perovskite-silicon tandems. Implementing perovskites as the front cell requires an inverted (p-i-n) architecture; this architecture is particularly effective at harnessing high-energy photons and is compatible with ionic-dopant-free transport layers. Here, a power conversion efficiency of 21.6% is reported, the highest among inverted perovskite solar cells (PSCs). Only by introducing a secondary amine into the perovskite structure to form MA(1-)(x)DMA(x)PbI(3) (MA is methylamine and DMA is dimethylamine) are defect density and carrier recombination suppressed to enable record performance. It is also found that the controlled inclusion of DMA increases the hydrophobicity and stability of films in ambient operating conditions: encapsulated devices maintain over 80% of their efficiency following 800 h of operation at the maximum power point, 30 times longer than reported in the best prior inverted PSCs. The unencapsulated devices show record operational stability in ambient air among PSCs.

Colloidal metal oxide nanocrystals offer a unique combination of excellent low-temperature solution processability, rich and tuneable optoelectronic properties and intrinsic stability, which makes them an ideal class of materials as charge transporting layers in solution-processed light-emitting diodes and solar cells. Developing new material chemistry and custom-tailoring processing and properties of charge transporting layers based on oxide nanocrystals hold the key to boosting the efficiency and lifetime of all-solution-processed light-emitting diodes and solar cells, and thereby realizing an unprecedented generation of high-performance, low-cost, large-area and flexible optoelectronic devices. This review aims to bridge two research fields, chemistry of colloidal oxide nanocrystals and interfacial engineering of optoelectronic devices, focusing on the relationship between chemistry of colloidal oxide nanocrystals, processing and properties of charge transporting layers and device performance. Synthetic chemistry of colloidal oxide nanocrystals, ligand chemistry that may be applied to colloidal oxide nanocrystals and chemistry associated with post-deposition treatments are discussed to highlight the ability of optimizing processing and optoelectronic properties of charge transporting layers. Selected examples of solution-processed solar cells and light-emitting diodes with oxide-nanocrystal charge transporting layers are examined. The emphasis is placed on the correlation between the properties of oxide-nanocrystal charge transporting layers and device performance. Finally, three major challenges that need to be addressed in the future are outlined. We anticipate that this review will spur new material design and simulate new chemistry for colloidal oxide nanocrystals, leading to charge transporting layers and solution-processed optoelectronic devices beyond the state-of-the-art. Funding Agencies|National Key Research and Development Program of China [2016YFB0401602, 2016YFA0204000]; National Natural Science Foundation of China [51522209, 91433204, U1632118, 21571129]; Fundamental Research Funds for the Central Universities [2015FZA3005]; Shanghai Key Research program [16JC1402100]; Shanghai International Cooperation Project [16520720700]; Carl Tryggers Stiftelse; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linko "ping University [2009-00971]

Hydrogen generation via photocatalysis-driven water splitting provides a convenient approach to turn solar energy into chemical fuel. The development of photocatalysis system that can effectively harvest visible light for hydrogen generation is an essential task in order to utilize this technology. Herein, a kind of cadmium free Zn-Ag-In-S (ZAIS) colloidal quantum dots (CQDs) that shows remarkably photocatalytic efficiency in the visible region is developed. More importantly, a nanocomposite based on the combination of 0D ZAIS CQDs and 2D MoS2 nanosheet is developed. This can leverage the strong light harvesting capability of CQDs and catalytic performance of MoS2 simultaneously. As a result, an excellent external quantum efficiency of 40.8% at 400 nm is achieved for CQD-based hydrogen generation catalyst. This work presents a new platform for the development of high-efficiency photocatalyst based on 0D-2D nanocomposite.

We are glad to announce the Special Issue "Nanostructured Solar Cells", published in Nanomaterials. This issue consists of eight articles, two communications, and one review paper, covering major important aspects of nanostructured solar cells of varying types. From fundamental physicochemical investigations to technological advances, and from single junction solar cells (silicon solar cell, dye sensitized solar cell, quantum dots sensitized solar cell, and small molecule organic solar cell) to tandem multi-junction solar cells, all aspects are included and discussed in this issue to advance the use of nanotechnology to improve the performance of solar cells with reduced fabrication costs.

Ternary alloy PbxCd1−xS quantum dots (QDs) were explored as photosensitizers for quantum-dot-sensitized solar cells (QDSCs). Alloy PbxCd1−xS QDs (Pb0.54Cd0.46S, Pb0.31Cd0.69S, and Pb0.24Cd0.76S) were found to substantially improve the photocurrent of the solar cells compared to the single CdS or PbS QDs. Moreover, it was found that the photocurrent increases and the photovoltage decreases when the ratio of Pb in PbxCd1−xS is increased. Without surface protecting layer deposition, the highest short-circuit current density reaches 20 mA/cm2 under simulated AM 1.5 illumination (100 mW/cm2). After an additional CdS coating layer was deposited onto the PbxCd1−xS electrode, the photovoltaic performance further improved, with a photocurrent of 22.6 mA/cm2 and an efficiency of 3.2%.

Small bandgap Sn-Pb mixed perovskite is generally regarded as the most promising structure to further enhance the power conversion efficiency of perovskite solar cells. However, the open circuit voltages (V(OC)s) are usually lower than expected. In this work, by doping the generally used hole transporting layer (HTL) poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) with a perfluorinated ionomer (PFI), we can tune the work function of it from -5.02 to -5.19eV. This reduces the energy level mismatch between the FA(0.6)MA(0.4) Sn0.6Pb0.4I3 (FAMA) absorber and HTL, giving rise to enhanced built-in voltage and better carrier extraction. The V-OC improves to over 50mV, up to 0.783V, resulting in an improved champion power conversion efficiency (PCE) of 15.85%. Moreover, the devices based on modified HTLs show improved stability at maximum power point. These results demonstrate that energy level tuning of the HTL is a promising strategy for the improvement of the PCEs of Sn-Pb mixed inverted PSCs, and the addition of PFI is an effective method to tune the work function of PEDOT:PSS.

The hybridization of 2D materials and colloidal quantum dots (CQDs) has been demonstrated to be an ideal platform for infrared photodetectors due to the high mobility of 2D materials and the excellent light harvesting capability of CQDs. However, the realization of ambipolar, broadband, and room-temperature graphene-quantum dot phototransistors with complementary metal-oxide-semiconductor (CMOS) compatibility remains challenging. Here N, S codecorated graphene is deposited with PbS CQDs to fabricate a hybrid phototransistor on a silicon dioxide/silicon gate. The resulting device demonstrates a gate-tuneable ambipolar feature with a low gate bias of less than 3.3 V at room temperature in ambient. Broadband spectra from visible to near-infrared and to short wave infrared (SWIR) light can be detected with gain value of up to 10(5) and a fast response of 3 ms. Upon illumination by SWIR light at 1550 nm, the phototransistor exhibits an ultrahigh responsivity that is on the order of 10(4) AW(-1) and a specific detectivity that is on the order of 10(12) Jones with a low driving voltage of 1 V. This decorated hybrid architecture illustrates the potential of graphene and CQDs to be integrated with silicon integrated circuits and opens a new path toward ambipolar photodetector fabrication.

Metal halide perovskites are rising as a competitive material for next-generation light-emitting diodes (LEDs). However, the development of perovskite LEDs is impeded by their fast carriers diffusion and poor stability in bias condition. Herein, quasi-2D CsPbBr3 quantum wells homogeneously surrounded by inorganic crystalline Cs4PbBr6 of large bandgap are grown. The centralization of carriers in nanoregion facilitates radiative recombination and brings much enhanced luminescence quantum yield. The external quantum efficiency and luminescence intensity of the LEDs based on this nanocomposite are one order of magnitude higher than the conventional low-dimensional perovskite. Meanwhile, the use of inorganic nanocomposite materials brings much improved device operation lifetime under constant electrical field.

Programming living cells to organize inorganic nano-objects (NOs) in a spatiotemporally precise fashion would advance new techniques for creating ordered ensembles of NOs and new bio-abiotic hybrid materials with emerging functionalities. Bacterial cells often grow in cellular communities called biofilms. Here, a strategy is reported for programming dynamic biofilm formation for the synchronized assembly of discrete NOs or hetero-nanostructures on diverse interfaces in a dynamic, scalable, and hierarchical fashion. By engineering Escherichia coli to sense blue light and respond by producing biofilm curli fibers, biofilm formation is spatially controlled and the patterned NOs' assembly is simultaneously achieved. Diverse and complex fluorescent quantum dot patterns with a minimum patterning resolution of 100 µm are demonstrated. By temporally controlling the sequential addition of NOs into the culture, multilayered heterostructured thin films are fabricated through autonomous layer-by-layer assembly. It is demonstrated that biologically dynamic self-assembly can be used to advance a new repertoire of nanotechnologies and materials with increasing complexity that would be otherwise challenging to produce.

Stabilization is one critical issue that needs to be improved for future application of colloidal quantum dot (QD)-based light-emitting diodes (QLEDs). This study reports highly efficient and stable QLEDs based on solution-processsed, metal-doped nickel oxide films as hole injection layer (HIL). Several kinds of metal dopants (Li, Mg, and Cu) are introduced to improve the hole injection capability of NiO films. The resulting device with Cu:NiO HIL exhibits superior performance compared to the state-of-the-art poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS)-based QLEDs, with a maximum current efficiency and external quantum efficiency of 45.7 cd A(-1) and 10.5%, respectively. These are the highest values reported so far for QLEDs with PEDOT:PSS-free normal structure. Meanwhile, the resulting QLED shows a half-life time of 87 h at an initial luminance of 5000 cd m(-2), almost fourfold longer than that of the PEDOT:PSS-based device.

Semiconducting lead triiodide perovskites (APbI(3)) have shown remarkable performance in applications including photovoltaics and electroluminescence. Despite many theoretical possibilities for A(+) in APbI(3), the current experimental knowledge is largely limited to two of these materials: methylammonium (MA(+)) and formamidinium (FA(+)) lead triiodides, neither of which adopts the ideal, cubic perovskite structure at room temperature. Here, a volume-based criterion is proposed for cubic APbI(3) to be stable, and two perovskite materials MA(1-x)EA(x)PbI(3) (MEPI, EA(+) = ethylammonium) and MA(1-y)DMA(y)PbI(3) (MDPI, DMA(+) = dimethylammonium) are introduced. Powder and single-crystal X-ray diffraction (XRD) results reveal that MEPI and MDPI are solid solutions possessing the cubic perovskite structure, and the EA(+) and DMA(+) cations play similar roles in the symmetrization of the crystal lattice of MAPbI(3). Single crystals of MEPI and MDPI are grown and made into plates of a range of thicknesses, and then into metal-perovskite photodiodes. These devices exhibit tripled diffusion lengths and about tenfold enhancement in stability against moisture, both relative to the current benchmark MAPbI(3). In this study, the systematic approach to materials design and device fabrication greatly expands the candidate pool of perovskite semiconductors, and paves the way for high-performance, single-crystal perovskite devices including solar cells and light emitters.