Search

HgTe colloidal quantum dots (CQDs) are promising absorber systems for infrared detection due to their widely tunable photoresponse in all infrared regions. Up to now, the best-performing HgTe CQD photodetectors have relied on using aggregated CQDs, limiting the device design, uniformity and performance. Herein, we report a ligand-engineered approach that produces well-separated HgTe CQDs. The present strategy first employs strong-binding alkyl thioalcohol ligands to enable the synthesis of well-dispersed HgTe cores, followed by a second growth process and a final postligand modification step enhancing their colloidal stability. We demonstrate highly monodisperse HgTe CQDs in a wide size range, from 4.2 to 15.0 nm with sharp excitonic absorption fully covering short- and midwave infrared regions, together with a record electron mobility of up to 18.4 cm

The magnetoresistance of HgTe quantum dot films, exhibiting a well-defined 1Se state charging and a relatively high mobility (1–10 cm2 V−1 s−1), is measured with controlled occupation of the first electronic state.

Top and bottom surfaces of polymer films are used to construct interfaces in heterojunction based devices, affecting device figure of merit significantly with their different aggregation states.

The present work reports highly efficient flexible and reabsorption-free scintillators based on two zero-dimensional (0D) organic copper halides (TBA)CuX2 (TBA = tetrabutylammonium cation; X = Cl, Br). The (TBA)CuX2 exhibit highly luminescent green and sky-blue emissions peaked at 510 and 498 nm, with large Stokes shifts of 224 and 209 nm and high photoluminescence quantum yields (PLQYs) of 92.8% and 80.5% at room temperature for (TBA)CuCl2 and (TBA)CuBr2 single crystals (SCs), respectively. Interestingly, above room temperature, their PLQYs increase with temperature and reach near unity at 320 and 345 K for (TBA)CuCl2 and (TBA)CuBr2, respectively. The excellent properties originate from self-trapped excitons (STEs) in individual [CuX2]- quantum rods, which is demonstrated by the temperature-dependent PL, ultrafast transient absorption (TA) combined with density functional theory (DFT) calculations. The (TBA)CuX2 scintillators show bright radioluminescence (RL), impressive linear response to dose rate in a broad range, and high light yields. Their potential application in X-ray imaging is demonstrated by using (TBA)CuX2 composite scintillation screens. Importantly, flexible scintillators are demonstrated to be superior than flat ones for imaging nonplanar objects by conformally coating, which produce accurate images with negligible distortion.

Infrared solar cells (IRSCs) can supplement silicon or perovskite SCs to broaden the utilization of the solar spectrum. As an ideal infrared photovoltaic material, PbS colloidal quantum dots (CQDs) with tunable bandgaps can make good use of solar energy, especially the infrared region. However, as the QD size increases, the energy level shrinking and surface facet evolution makes us reconsider the matching charge extraction contacts and the QD passivation strategy. Herein, different to the traditional sol-gel ZnO layer, energy-level aligned ZnO thin film from a magnetron sputtering method is adopted for electron extraction. In addition, a modified hybrid ligand recipe is developed for the facet passivation of large size QDs. As a result, the champion IRSC delivers an open circuit voltage of 0.49 V and a power conversion efficiency (PCE) of 10.47% under AM1.5 full-spectrum illumination, and the certified PCE is over 10%. Especially the 1100 nm filtered efficiency achieves 1.23%. The obtained devices also show high storage stability. The present matched electron extraction and QD passivation strategies are expected to highly booster the IR conversion yield and promote the fast development of new conception QD optoelectronics.

Lead selenide (PbSe) colloidal quantum dots (CQDs) are promising candidates for optoelectronic applications. To date, PbSe CQDs capped by halide ligands exhibit improved stability and solar cells using these CQDs as active layers have reported a remarkable power conversion efficiency (PCE) up to 10%. However, PbSe CQDs are more prone to oxidation, requiring delicate control over their processability and compromising their applications. Herein, an efficient strategy that addresses this issue by an in situ cation-exchange process is reported. This is achieved by a two-phase ligand exchange process where PbI

Improved mid-infrared photoconductors based on colloidal HgTe quantum dots are realized using a hybrid ligand exchange and polar phase transfer. The doping can also be controlled n and p by adjusti...

Summary Defect sites are often proposed as key active sites in the design of catalysts. A promising strategy for improving activity is to achieve a high density of homogeneously dispersed atomic defects; however, this is seldom accomplished in metals. We hypothesize that vacancy-rich catalysts could be obtained through the synthesis of quantum dots (QDs) and their electrochemical reduction during the CO2 reduction reaction (CO2RR). Here, we report that QD-derived catalysts (QDDCs) with up to 20 vol % vacancies achieve record current densities of 16, 19, and 25 mAcm−2 with high faradic efficiencies in the electrosynthesis of formate, carbon monoxide, and ethylene at low potentials of –0.2, –0.3, and –0.9 V versus reversible hydrogen electrode (RHE), respectively. The materials are stable after 80 hr of CO2RR. These CO2RR performances in aqueous solution surpass those of previously reported catalysts by 2×. Together, X-ray absorption spectroscopy and computational studies reveal that the vacancies produce a local atomic and electronic structure that enhances CO2RR.

Broad-band white-light emissions from organic-inorganic lead halide hybrids have attracted considerable attention in energy-saving solid-state lighting (SSL) applications. However, the toxicity of lead in these hybrids hinders their commercial prospects, and the low photoluminescence quantum yields (PLQYs) cannot meet the requirements for efficient lighting. Here, we report a highly efficient dual-band white-light emission from organic copper iodide, (C16H36N)CuI2, which exhibits a high PLQY of 54.3% and excellent air stability. The single-crystalline (C16H36N)CuI2 possesses a unique zero-dimensional (0D) structure, in which the isolated [Cu2I4]2- dimers are periodically embedded in the wide band gap organic framework of C16H36N+. This perfect 0D structure can cause significant quantum confinement and strong electron-phonon coupling, which contributes to efficient emissions from self-trapped excitons (STEs). Photophysical studies revealed the presence of two self-trapped emitting states in [Cu2I4]2- dimers, whose populations are highly sensitive to the temperature that governs the molecular environment for [Cu2I4]2- dimers and the thermal activation energy of STEs. An ultraviolet (UV) excited white light-emitting diode fabricated using this single-phase white-light emitter exhibits a high color rendering index (CRI) of 78. The new material provides a promising emitter, having a high PLQY and a high CRI simultaneously, for SSL and display applications.

Solution-processed colloidal quantum dots (CQDs) are promising candidates for the third-generation photovoltaics due to their low cost and spectral tunability. The development of CQD solar cells mainly relies on high-quality CQD ink, smooth and dense film, and charge-extraction-favored device architectures. In particular, advances in the processing of CQDs are essential for high-quality QD solids. The phase transfer exchange (PTE), in contrast with traditional solid-state ligand exchange, has demonstrated to be the most promising approach for high-quality QD solids in terms of charge transport and defect passivation. As a result, the efficiencies of Pb chalcogenide CQD solar cells have been rapidly improved to 14.0%. In this review, the development of the PTE method is briefly reviewed for lead chalcogenide CQD ink preparation, film assembly, and device construction. Particularly, the key roles of lead halides and additional additives are emphasized for defect passivation and charge transport improvement. In the end, several potential directions for future research are proposed.

An improved vapor-phase deposition that leveraged the use of surface activation of PbI2 film has been developed for modifying perovskite crystallization process. This was achieved by loading Cl− ligands on closely-packed PbI2 particle film—a scaffold that allowed in situ formation of perovskite active layer. The introducing of Cl− ligands served the Cl-capped and thus electrostatically-charged PbI2 nanoparticles showed improved colloidal stability in DMF, which facilitated the preparation of PbI2 film. More importantly, during the process of CH3NH3I (MAI) deposition i.e. the growth of perovskite materials, the presence of three-dimensional Cl− ligand matrix favored the formation of dense perovskite film. Moreover, a desired release of chloride was also achieved, thus promote the rearrangement of the perovskite during the volume expansion process. This finally led to a PCE of PSCs exceeding 16.42% under AM 1.5 irradiation. Therefore, surface-activation with Cl-ligand matrix could provide guidelines for the morphology optimization and the perovskite devices performance enhancement.

Colloidal quantum dots can be stabilized in either a polar solvent or a nonpolar solvent depending on their surface chemistry. The former is typically achieved by charge stabilization while the latter by steric hindrance. This allows reversible tuning of their surface polarity for targeted application by engineering their ligand profile. Here we developed a hybrid stabilization approach that leveraged a combination of steric hindrance and charge stabilization simultaneously. We demonstrated this mechanism in a phase transfer process where hexane dispersed and hydrophobic CdSe/CdS core/shell quantum dots were exchanged into the hydrophilic dimethylformamide (DMF) phase. This was achieved by employing both Z-type cadmium acetate and X-type halide ligands. The results suggested only by using this hybrid stabilization strategy were we able to achieve good colloidal stability while preserving their photoluminescence quantum yield. This hybrid ligand strategy may promise new opportunities for the application of QDs in optoelectronic areas.

Solution-processed colloidal quantum dots (CQDs) are promising candidates for large-scale, low-cost, and lightweight photovoltaic and electronic devices. Carrier transport dynamics has a substantial impact on device efficiency optimization. Coupled with photocarrier radiometry (PCR) — a dynamic spectrally integrated frequency-domain photoluminescence (PL) modality, we report the derivation of a trap-state-mediated carrier hopping transport model for the extraction of multiple carrier transport parameters in PbS CQD thin films. These parameters, including effective carrier lifetime τE, hopping diffusivity Dh, trap-state-dependent carrier trapping rate RT, diffusion length Lh, and carrier thermal emission rate e i , were obtained for CQD thin films with different dot size and capping ligands: tetrabutylammonium iodide (TBAI), 1,2-ethanedithiol (EDT), and methylammonium lead triiodide perovskite (MAPbI3). Consistent with the framework of phonon-assisted carrier hopping mechanism, τE, Dh, and Lh have demonstrated a monotonic dependence on temperature in the range from 100 K to 300 K. Perovskite-passivated PbS CQD thin films, especially those with larger dot sizes which are free of apparent defect induced PL emission and have higher τE and Dh at room temperature (ca. 0.51 μs and 1.80×10−2 cm2/s, respectively) than their counterparts, demonstrate better photovoltaic material properties. Dot-size-dependent exciton binding energies (35.21–53.20 meV) were characterized using a dynamic PCR photo-thermal spectroscopy that also characterized the trap-state-mediated carrier hopping activation energies in the range from 100 meV to 280 meV. To test the reliability of the best-fitted results, computational fitting uniqueness was examined using a parametric theory.

Anomalous current-voltage (I-V) characteristics, as reported with increasing frequency, can significantly compromise the energy conversion efficiency of colloidal quantum dot (CQD) solar cells. This paper applied a purely hopping transport model rather than the traditional Schottky-diode equation to interpret the anomalous I-V curves measured in CQD solar cells with a structure: ITO/ZnO/PbS-TBAI QD/PbS-EDT QD/Au. Anomalous I-V curves were found at temperatures below 300 K. A double-diode-equivalent electric circuit was developed for the quantitative analysis of these anomalous I-V curves, yielding multiple hopping transport parameters, such as hopping diffusivity, diffusion length, mobility, and lifetime. Quantitative analysis revealed that the imbalanced charge carrier mobility in the carrier transport (PbS-TBAI) and extraction (PbS-EDT) layers, as well as the existence of a reverse Schottky diode at the PbS-EDT/Au interface, played key roles in the formation of the anomalous I-V curves. Furthermore, charge-transfer (CT) states, located at the ZnO/PbS-TBAI interface, were found to reduce the CQD solar cell open-circuit voltage through radiative and non-radiative recombination of excitons. A modified Einstein equation was also validated, further proving the presence of a Schottky barrier and pointing to a rate determining interface for the I-V behaviors of our solar cells.

Colloidal quantum dot (CQD) solar cells are solution-processed photovoltaics with broad spectral absorption tunability. Major advances in their efficiency have been made via improved CQD surface passivation and device architectures with enhanced charge carrier collection. Herein, we demonstrate a new strategy to improve further the passivation of CQDs starting from the solution phase. A cosolvent system is employed to tune the solvent polarity in order to achieve the solvation of methylammonium iodide (MAI) and the dispersion of hydrophobic PbS CQDs simultaneously in a homogeneous phase, otherwise not achieved in a single solvent. This process enables MAI to access the CQDs to confer improved passivation. This, in turn, allows for efficient charge extraction from a thicker photoactive layer device, leading to a certified solar cell power conversion efficiency of 10.6%, a new certified record in CQD photovoltaics.

Perovskite-shelled colloidal quantum dots (CQDs) with low trap-state density are promising candidates for large-scale, low-cost, and lightweight solar cell applications. However, even minimal trap states can significantly limit CQD-based solar cell efficiency. We reported trap-state-mediated exciton transports in methylammonium lead triiodide (MAPbI3) perovskite-passivated PbS CQD thin films. Excitation power-dependent photocarrier radiometry (PCR) intensity study demonstrated the free (electrons/holes)-to-bound (acceptors/donors) and trap-state-related transition-induced nonlinear response of CQD thin films to excitation. The existence of shallow trap states (activation energy: 33.8–40.7 meV) was characterized using photothermal emission spectra at different modulation frequencies. CQD thin films were imaged, for the first time, by InGaAs-camera-based nondestructive homodyne and heterodyne lock-in carrierographies (LIC; spectrally gated dynamic photoluminescence imaging), clearly showcasing photocarrier ...

Graphdiyne, a novel large π-conjugated carbon hole transporting material, is employed as anode buffer layer in colloidal quantum dots solar cells. Power conversion efficiency is notably enhanced to 10.64% from 9.49% compared to relevant reference devices. Hole transfer from the quantum dot solid active layer to the anode can be appreciably enhanced only by using graphdiyne to lower the work function of the colloidal quantum dot solid. It is found that the all-carbon buffer layer prolongs the carrier lifetime, reducing surface recombination on the previously neglected back side of the photovoltaic device. Remarkably, the device also shows high long-term stability in ambient air. The results demonstrate that graphdiyne may have diverse applications in enhancing optoelectronic devices.

A crosslinked hole-extracting electrical contact is reported, which simultaneously improves the stability and lowers the hysteresis of perovskite solar cells. Polymerizable monomers and crosslinking processes are developed to obviate in situ degradation of the under lying perovskite. The crosslinked material is band-aligned with perovskite. The required free carrier density is induced by a high-work-function metal oxide layer atop the device, following a remote-doping strategy.

Precise patterning of quantum dot (QD) layers is an important prerequisite for fabricating QD light-emitting diode (QLED) displays and other optoelectronic devices. However, conventional patterning methods cannot simultaneously meet the stringent requirements of resolution, throughput, and uniformity of the pattern profile while maintaining a high photoluminescence quantum yield (PLQY) of the patterned QD layers. Here, a specially designed nanocrystal ink is introduced, "photopatternable emissive nanocrystals" (PENs), which satisfies these requirements. Photoacid generators in the PEN inks allow photoresist-free, high-resolution optical patterning of QDs through photochemical reactions and in situ ligand exchange in QD films. Various fluorescence and electroluminescence patterns with a feature size down to ≈1.5 µm are demonstrated using red, green, and blue PEN inks. The patterned QD films maintain ≈75% of original PLQY and the electroluminescence characteristics of the patterned QLEDs are comparable to thopse of non-patterned control devices. The patterning mechanism is elucidated by in-depth investigation of the photochemical transformations of the photoacid generators and changes in the optical properties of the QDs at each patterning step. This advanced patterning method provides a new way for additive manufacturing of integrated optoelectronic devices using colloidal QDs.

Radioluminescent materials (scintillators) are widely applied in medical imaging, nondestructive testing, security inspection, nuclear and radiation industries, and scientific research. Recently, all‐inorganic lead halide perovskite nanocrystal (NC) scintillators have attracted great attention due to their facile solution processability and ultrasensitive X‐ray detection, which allows for large area and flexible X‐ray imaging. However, the light yield of these perovskite NCs is relatively low because of the strong self‐absorption that reduces the light out‐coupling efficiency. Here, NCs with self‐trapped excitons emission are demonstrated to be sensitive, reabsorption‐free scintillators. Highly luminescent and stable Cs3Cu2I5 NCs with a photoluminescence quantum yields of 73.7%, which is a new record for blue emission lead‐free perovskite or perovskite‐like NCs, is produced with the assistance of InI3. The PL peak of the Cs3Cu2I5 NCs locates at 445 nm that matches with the response peak of a silicon photomultiplier. Thus, Cs3Cu2I5 NCs are demonstrated as efficient scintillators with zero self‐absorption and extremely high light yield (≈79 279 photons per MeV). Both Cs3Cu2I5 NC colloidal solution and film exhibit strong radioluminescence under X‐ray irradiation. The potential application of Cs3Cu2I5 NCs as reabsorption‐free, low cost, large area, and flexible scintillators is demonstrated by a prototype X‐ray imaging with a high spatial resolution., Nanocrystals (NCs) with self‐trapped excitons emission are demonstrated to be sensitive, reabsorption‐free scintillators. Highly blue‐emissive and stable Cs3Cu2I5 NCs with a photoluminescence quantum yield of 73.7% are produced. These Cs3Cu2I5 NCs show a strong and reabsorption‐free radioluminescence under X‐ray irradiation with an extremely high light yield, which makes them promising scintillators for low cost, large area, and flexible X‐ray imaging.

International audience; AbstractHgTe colloidal quantum dots (QDs) are of interest because quantum confinement of semimetallic bulk HgTe allows one to synthetically control the bandgap throughout the infrared. Here, we synthesize highly monodisperse HgTe QDs and tune their doping both chemically and electrochemically. The monodispersity of the QDs was evaluated using small-angle X-ray scattering (SAXS) and suggests a diameter distribution of similar to 10% across multiple batches of different sizes. Electron-doped HgTe QDs display an intraband absorbance and bleaching of the first two excitonic features. We see splitting of the intraband peaks corresponding to electronic transitions from the occupied 1Se state to a series of nondegenerate 1Pe states. Spectroelectrochemical studies reveal that the degree of splitting and relative intensity of the intraband features remain constant across doping levels up to two electrons per QD. Theoretical modeling suggests that the splitting of the 1Pe level arises from spin-orbit coupling and reduced QD symmetry. As a result, the fine structure of the intraband transitions is observed in the ensemble studies due to the size uniformity of the as-synthesized QDs and strong spin-orbit coupling inherent to HgTe.

We explored a facile routine to synthesize morphology-controlled Ag2S-CdS heterostructures. The heterostructures were achieved by a two-step method where CdS nanorods were prepared in the first step, acting as the substrates inducing successive cation exchange reaction between Cd2+ and Ag+ ion. The nucleation sites of Ag2S can be readily controlled by varying the feed ratios of Ag+ to Cd2+ ion, thus leading to formation of heterostructures with different morphology where Ag2S particles grow on the tips of the CdS rods, or at multiple locations across the nanorods. HRTEM analysis showed that Ag2S particles were grown on the varied sites of CdS rods with a coherent, quasi-epitaxial interface having different degrees of lattice mismatch. Photoluminescence results showed that, compared to bare CdS nanorods, enhanced trap emissions were observed after the growth of Ag2S particles on the rods, which can be attributed to the strained interfaces instead of impurities doping.

The development of novel sodium-ion batteries has been hindered by the lack of ideal anode materials. Herein, we report both experimental and theoretical assessment of layered MoSe 2 nanoplates as the anode materials. The MoSe 2 nanoplates are successfully synthesized by a facile thermal-decomposition process. As the anode, the MoSe 2 nanoplates are capable of delivering the initial discharge and charge capacities of 513 and 440 mAh g −1 at the current of 0.1C in a voltage of 0.1–3 V, respectively. The analysis of Ex-situ XRD patterns reveals that there is no slippage between layers and the change of coordination of molybdenum when the MoSe 2 electrode is discharged to 0.6 V and conversion reactions during the following discharge/charge process are also demonstrated. In addition, the electronic structure, Na ions transport and conductivity are investigated by first-principles calculation. A quasi-2D energy favorable trajectory is proposed to illustrate the sodium ion vacancy-hopping migration mechanism form octahedron to tetrahedron in MoSe 2 lattice. The results suggest great potential of MoSe 2 as an anode material for Na ion batteries.

Colloidal quantum dots (CQD) are an attractive thin-film material for photovoltaic applications due to low material costs, ease of fabrication, and size-tunable band gap. Unfortunately, today they suffer from a compromise between light absorption and photocarrier extraction, a fact that currently prevents the complete harvest of incoming above-band-gap solar photons. We have investigated the use of structured substrates and/or electrodes to increase the effective light path through the active material and found that these designs require highly conformal application of the light-absorbing films to achieve the greatest enhancement. This conformality requirement derives from the need for maximal absorption enhancement combined with shortest-distance charge transport. Here we report on a means of processing highly conformal layer-by-layer deposited CQD absorber films onto microstructured, light-recycling electrodes. Specifically, we engineer surface hydrophilicity to achieve conformal deposition of upper layers atop underlying ones. We show that only with the application of conformal coating can we achieve optimal quantum efficiency and enhanced power conversion efficiency in structured-electrode CQD cells.

The real applications of Na3V2(PO4)3 cathode material for sodium batteries have been hindered by low-cost and facile synthesis method. Herein, we report a facile self-combustion method to synthesize Na3V2(PO4)3 nanoparticles coated with carbon shell (NVP/C). Using as the cathode, the NVP/C is capable of delivering the initial discharge and charge capacities of 100.72 and 111.3 mAh g−1 at the current of 0.1 C in a voltage of 2.5–3.8 V, and the capacity retention of the sample is approximately 95% of its initial specific capacity after 50th cycles. The first-principles simulation results show that the Na ions migration route prefers between two adjacent tetrahedral sites with the vacancy-hopping mechanism in a curved way, with the lowest activation energy of 0.292 eV. The diffusion coefficients DNa+ at room temperature was also calculated as higher as 2.38 × 10−9 cm2 s−1. The results suggest great potential of self-combustion synthesized NVP/C as cathode materials for Na-ion batteries.

Topological map is the basis of navigation and can be used for positioning. At present, the acquisition of map mainly relies on manual or machine measurement, which is costly. And for indoor situation, re-measurements are needed when the topology of the building changes. Aiming at the above problems and fully considering the widely use of smart mobile phone terminals and applications, this paper proposes a method for establishing topological map based on crowdsourcing data. Through conducting similarity analysis and matching of magnetic field intensity and WLAN/Bluetooth signal in crowdsourcing data, this method establishes connections between crowdsourcing data, and then construct a topological map with the main features of road segments. Experimental analysis shows that the method proposed can realize the self-generation of topology of general buildings by using data collected by ordinary users.

A novel electrode material for sodium-ion batteries (NIBs), Na3V2(PO4)3 with a rhombohedral, Na+ superionic conductor (NASICON)-type structure, was synthesised via a solid-state carbon-thermal reduction reaction assisted by mechanochemical activation. Electron microscopy analysis showed that the synthesised Na3V2(PO4)3 particles had an average size of 300 nm, being coated with a uniform layer of carbon 3 nm in thickness. As a cathode material, Na3V2(PO4)3/C exhibited an initial specific discharge capacity of 98.17 mAh g−1 at 0.1C for potentials ranging from 2.5 to 3.8 V. This was owing to the V3+/V4+ redox couple, which corresponded to the two-phase transition between Na3V2(PO4)3 and NaV2(PO4)3. The cathode lost 4.92% of its discharge specific capacity after 50 cycles. As an anode material, Na3V2(PO4)3/C exhibited an initial specific discharge capacity of 63.2 mAh g−1 at 0.1C for potentials ranging from 1.0 to 2.5 V. This was owing to the V2+/V3+ redox couple, which corresponded to the two-phase transition between Na3V2(PO4)3 and Na4V2(PO4)3. The anode lost approximately 5.41% of its discharge specific capacity after 50 cycles. The three-dimensional channel structure of NaV2(PO4)3 and the changes induced in its lattice parameters during the charge/discharge processes were simulated on the basis of density functional theory.

Vertically aligned nanowire arrays (NWAs) of semiconductor materials, combined with the merits of the large surface-to-volume ratio and low reflectance induced by light scattering and trapping, have attracted growing interests in the fabrication of high-performance optoelectronic nano-devices due to their exceptional geometrical structure and device architecture. However, an inexpensive synthesis of II–VI group semiconductor NWAs, e.g. CdS, CdSe NWAs, especially their heterostructures, is still a great challenge, and the devices (photodetector, field emitter, etc.) based on these NWA heterostructures have therefore been rarely studied. Here, we report a new method of synthesizing high-quality vertical CdS NWAs which heteroepitaxially grow on CdSe single-crystalline sheets (SCSs). The CdS NWA/CdSe SCS heterostructures as a whole are designed and fabricated into novel photodetectors via E-beam lithography. The obtained photodetectors exhibit excellent performance with high photosensitivity, responsivity, and external quantum efficiency, alongside fast response speed, and wide range response spectrum. Additionally, field-emission data of these vertically tapered CdS NWAs on CdSe SCS show enhanced properties with low turn-on field, high enhancement factor, and good stability. The results indicate that the synthesized CdS NWA/CdSe SCS heterostructure is a good candidate for broadband (ultraviolet-visible) photodetectors and field-emitters.

The solar-power conversion efficiencies of colloidal quantum dot solar cells have advanced from sub-1% reported in 2005 to a record value of 8.5% in 2013. Much focus has deservedly been placed on densifying, passivating and crosslinking the colloidal quantum dot solid. Here we review progress in improving charge extraction, achieved by engineering the composition and structure of the electrode materials that contact the colloidal quantum dot film. New classes of structured electrodes have been developed and integrated to form bulk heterojunction devices that enhance photocharge extraction. Control over band offsets, doping and interfacial trap state densities have been essential for achieving improved electrical communication with colloidal quantum dot solids. Quantum junction devices that not only tune the optical absorption spectrum, but also provide inherently matched bands across the interface between p- and n-materials, have proven that charge separation can occur efficiently across an all-quantum-tuned rectifying junction.

Monodispersed and luminescent Ag-doped CdSe semiconductor quantum dots (d-dots) were synthesized by an aqueous route assisted with electrochemical preparation of Se source with 3-mercaptopropionic acid as stabilizer. The silver dopants were incorporated into the host crystals via cation-exchange mechanism. X-ray diffraction patterns revealed that the as-synthesized CdSe:Ag d-dots were well retained in the zinc blende structure. The CdSe:Ag d-dots that exhibited uniform size distribution and good crystallnity could be observed by High-resolution transmission electron microscopy (HRTEM), with average diameter of 2.7 nm. Successful doping was confirmed by X-ray photoelectron spectroscopy survey spectra. The peculiar Ag-related photoluminescence showed strong intensity, and at the same time, intrinsic band-edge exciton emission of CdSe QDs was suppressed. The dopant emission exhibited larger Stockes shift of - 0.51 eV than that of the band-gap emission, and varied from 546 to 583 nm by changing electrolytic time. Possible radiative recombination mechanism of the aqueous Ag-doped CdSe d-dots was discussed. The results demonstrated that doping can be an effective way to manipulate the optical properties of semiconductor nanocrystals.