Doped CdSe Research Articles

Unexpected Magnetic Moments in Manganese‐Doped (CdSe)13 Nanoclusters: Role of Ligands

This study explores the enhancement in magnetic and photoluminescence properties of Mn2+‐doped (CdSe)13 nanoclusters, significantly influenced by the introduction of paramagnetic centers through doping, facilitated by optimized precursor chemistry and precisely controlled surface ligand interactions. Using a cost‐effective and scalable synthesis approach with elemental Se and NaBH4 (Se‐NaBH4) in n‐octylamine, we tailored bonding configurations (Cd‐O, Cd‐N, and Cd‐Se) on the surface of nanoclusters, as confirmed by EXAFS analysis. These bonding configurations allowed for tunable Mn2+‐doping with tetrahedral coordination, further stabilized by hydrogen‐bonded acetate ligands, as evidenced by 13C NMR and IR spectroscopy. Mulliken charge analysis indicates that the charge redistribution on Se2‐ suggests electron transfer between surface ligands and the nanocluster, contributing to spin fluctuations. These tailored configurations markedly increased the nanoclusters' magnetic susceptibility and photoluminescence efficiency. The resulting nanoclusters demonstrated a clear concentration‐dependent response in emission lifetimes and intensities upon exposure to magnetic field effects (MFE) and spin‐spin coupling, alongside a large magnetic moment exceeding 40 μB at 180K. These findings highlight the potential of these nanoclusters for magneto‐optical devices and spintronic applications, showcasing their tunable magnetic properties and exciton dynamics.

Cd(Eu)Se/CdS/CdZnS/ZnS quantum dots with hydrophilic alloy shell supported by flower-like ZnIn2S4: A S-scheme for efficient photocatalytic H2 evolution

Photocatalytic hydrogen evolution via water splitting based on semiconductor technologies is a vital way to tackle environmental problems and the energy crisis in a sustainable manner. Carrier separation efficiency, light absorption capacity and microstructure of photocatalysts are key factors affecting the efficiency of photocatalytic hydrogen evolution. However, there exist problems like low separation of photogenerated electrons and holes and limited light absorption for traditional semiconductors. Here we prepared Eu3+ doped CdSe quantum dots with hydrophilic alloy shell CdS/CdZnS/ZnS and anchored it on flower-like ZnIn2S4 to construct S-scheme heterojunction. Characterizations of photocatalytic performance indicate that the hydrogen production performance is improved. What can be found is that the optimized composite photocatalyst has photocatalytic hydrogen evolution efficiency of 3888.79 μmol‧g−1‧h−1 and it is 6 times higher than unmodified ZnIn2S4. Furthermore, the creation of S-scheme heterojunction improves the disadvantages of ZnIn2S4 in visible light absorption and accelerates charge separation markedly. This work provides a distinctive perspective on the photocatalysts of photocatalytic hydrogen evolution.

Exploration of doping-dependent structural, optical, and electrical properties of thermally evaporated CdSe thin films for improved photodetection performance

This paper is devoted to studying the influence of indium doping on the structure, morphology, and electrical properties of thermally deposited CdSe thin films as a powerful approach toward optimized photodetection performance. The variation of incorporated In-level modulated crystallographic and surface morphology as obtained from the X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM), respectively. Besides, the optical properties of the prepared In:CdSe thin films were investigated spectrophotometrically in the UV-Vis-NIR regions. We have deeply evaluated not only the dispersion and absorption features but also the opto-(electronic) parameters of the prepared films. The spectral nonlinear optical refractive index, absorption coefficient, and susceptibility were estimated and analyzed. The tunability of the structural and optical properties is introduced in a systematic explainable manner in terms of the recorded elemental analysis using EDX. The dark conductivity measurements of the prepared films declared that doped CdSe film of 37.5 wt% indium achieved the highest electrical conductivity which coincident with all the structural and optical characterization findings. Furthermore, the fabricated In:CdSe films were integrated with p-type silicon for Au/In:CdSe/p-Si/Al heterojunction formation. The electrical and microelectronic parameters of the designed junctions have been assessed using the measured current-voltage relations. The charge carriers' conduction mechanism within the constructed junctions has been explained in detail. Eventually, the photodetection performance of the fabricated heterojunctions has been tested using the recorded (I-V) and (I-t) response curves. Evidently, 37.5 wt% In doping concentration in the CdSe structure achieved superior optical and electrical properties which have been reflected in its promising photodetection performance compared to not only the other pure and doped films in the present study but also other prior reports. Such a device achieved Jphoto, Rλ, EQE, D*, and tr/tf of about 34.4 mA/cm2, 3.43 A/W, 800%, 4.6 × 1010 Jones, and 3.06 ms/6.10 ms, respectively.

Synthesis, Assembly, and Applications of Magic-Sized Semiconductor (CdSe)13 Cluster.

ConspectusAtomically precise metal chalcogenide clusters (MCCs) are model molecular compounds of scientifically and technologically important semiconductor nanocrystals, which are known as quantum dots (QDs). The significantly high ambient stability of MCCs of particular sizes, as compared to that of slightly smaller or larger sizes, made them be termed "magic-sized clusters" (MSCs). In other words, MSCs with specific sizes between sizes of precursors (typically, metal-ligand complexes) and nanocrystals (typically, QDs) appear sequentially during the colloidal synthesis of nanocrystals, while the other cluster species decompose to precursor monomers or are consumed during the growth of the nanocrystals. Unlike nanocrystals with an ambiguous atomic-level structure and a substantial size distribution, MSCs possess atomically monodisperse size, composition, and distinct atomic arrangement. Chemical synthesis and exploration of properties of MSCs are of great significance since they help systematically understand the evolution of fundamental properties as well as build structure-activity relationships at distinct molecular levels. Furthermore, MSCs are anticipated to offer atomic-level insights into the growth mechanism of the semiconductor nanocrystals, which is highly desirable in the design of advanced materials with new functions. In this Account, we cover our recent efforts in the advancement of one of the most important stoichiometric CdSe MSCs, (CdSe)13. In particular, we present its molecular structure derived from a single crystal X-ray crystallographic study of the closest MSC, Cd14Se13. The crystal structure of MSC enables not only the understanding of the electronic structure and prediction of the potential sites for heteroatom dopants (e.g., Mn2+ and Co2+) but also the identification of favorable synthetic conditions for the selective synthesis of desired MSCs. Next, we focus on enhancing the photoluminescence quantum yield and stability of Mn2+ doped (CdSe)13 MSCs through their self-assembly, which is facilitated by the rigid diamines. In addition, we show how atomic-level synergistic effects and functional groups of the assemblies of alloy MSCs can be utilized for a highly enhanced catalytic CO2 fixation with epoxides. Benefiting from the intermediate stability, the MSCs are explored as single-source precursors to low-dimensional nanostructures, such as nanoribbons and nanoplatelets, through the controlled transformation. Distinct differences in the outcome of the solid-state and colloidal-state conversion of MSCs suggest the need for careful consideration of the phase and reactivity of MSCs as well as the type of dopant to achieve novel structured multicomponent semiconductors. Finally, we summarize the Account and provide future perspectives on the fundamental and applied scientific research of MSCs.

The impact of spatially heterogeneous chemical doping on the electronic properties of CdSe quantum dots: insights from ab initio computation.

The introduction of copper (Cu) impurity in semiconductor CdSe quantum dots (QDs) gives rise to unique photoluminescence (PL) bands exhibiting distinctive characteristics, like broad line width, significant Stokes shift, and complex temporal decay. The atomistic origins of these spectral features are yet to be understood comprehensively. We employed multiple computational techniques to systematically study the impact of the spatial heterogeneity of Cu atoms on the stability and photophysical properties, including the emission linewidth of doped QDs under ambient conditions. The Cu substitution introduces a spin-polarized intragap state, the energetic position of which is strongly dependent on the dopant location and causes spectral broadening in QD ensembles. Furthermore, the dopant dynamics under ambient conditions are significantly influenced by the specific arrangement of Cu within the QDs. The dynamic electronic structures of surface-doped CdSe illustrate more pronounced perturbations and vary the mid-gap state position more drastically than those of the core-doped QDs. Vibronic coupling broadens the photoluminescence peaks associated with the conduction band-to-defect level transition for individual QDs. These insights into the dynamic structure-photophysical property relationship suggest viable approaches, such as tuning the operational temperature and selective co-doping, to enhance the functional performances of doped CdSe QDs strategically.

Investigating the role of copper in arsenic doped Cd(Se,Te) photovoltaics

The open circuit voltage (VOC) deficit in Cd(Se,Te)-based photovoltaics remains a critical obstacle for pushing the technology closer to theoretical performance limits. Arsenic doping has become a dominant and promising route to achieve the higher p-type carrier concentrations necessary for higher VOC, but challenges associated with this alternate defect chemistry and higher doping density have hindered progress. Here we show that while arsenic doping enables high carrier concentrations (>1016 cm−3), co-doping with copper can provide a boost to VOC without a significant change to carrier concentration. A large data set is initially used to explore current-voltage and capacitance-voltage trends associated with arsenic doped devices with and without copper. A smaller subset is then used to probe these trends using a wide variety of characterization techniques. Copper is found to facilitate reduced interface recombination and potentially improved bulk absorber characteristics, though the mechanisms for these improvements are not yet clear. Despite the improved performance of co-doped devices, VOC is still far below its potential especially for highly doped devices. Low emitter doping in conjunction with high absorber doping seems to be a plausible cause for this significant deficit, though other device properties may exacerbate this problem.

Structure of a subnanometer-sized semiconductor Cd14Se13 cluster

Structure of a subnanometer-sized semiconductor Cd14Se13 cluster

Synthesis and characterization of Mn composition effect on CdSe thin films

Cadmium Selenide (CdSe) doped with (Mn) Manganese Chloride grown, on commercial glass substrate usingChemical Bath Deposition Method. Growth time was kept at 1-2 hours. Magnese Chloride (Mncl2) was used for dopant. CdMnSe films so obtained were characterized using X-Ray Diffraction, Scanning Electron Microscopy, EdAX, andUV-Visible spectrophotometer and photoluminescence studies respectively. XRD study confirms that CdSe films are polycrystalline in nature and have cubic structure. The Debye-Scherer formula was used to calculate average particle size of pure and doped CdSe film. Thus, the particle size was decrease on doping. The effect of doping concentration Mn on the luminescence spectra of CdSe was studied. The emission spectra revealed that the intensity increased considerably in the presence of dopant ions. It is clearly observed from the surface morphological studies by SEM that the as-deposited CdSe and doped Mn concentration films are nanocrystalline, homogenous, without cracks or holes and well covered to the glass substrate. FE-SEM images show spherical particles having uniform distribution. Roughness of the films were totally eliminated. EDAX patterns confirms the presence of Cadmium, Selenide and Magnese chloride elements (2%, 5%)in sample. Optical band gap of pure CdSe film comes out to be 2.1 eV.After doping energy band gap was decreasing. Copyright © 2017 VBRI Press.

Development of arsenic doped Cd(Se,Te) absorbers by MOCVD for thin film solar cells

Recent developments in CdTe solar cell technology have included the incorporation of ternary alloy Cd(Se,Te) in the devices. CdTe absorber band gap grading due to Se alloying contributes to current density enhancement and can result in device performance improvement. Here we report Cd(Se,Te) polycrystalline thin films grown by a chamberless inline atmospheric pressure metal organic chemical vapour deposition technique, with subsequent incorporation in CdTe solar cells. The compositional dependence of the crystal structure and optical properties of Cd(Se,Te) are examined. Selenium graded Cd(Se,Te)/CdTe absorber structure in devices are demonstrated using either a single CdSe layer or CdSe/Cd(Se,Te) bilayer (with or without As doping in the Cd(Se,Te) layer). Cross-sectional TEM/EDS, photoluminescence spectra and secondary ion mass spectroscopy analysis confirmed the formation of a graded Se profile toward the back contact with a diffusion length of ~1.5 μm and revealed back-diffusion of Group V (As) dopants from the CdTe layer into Cd(Se,Te) grains. Due to the strong Se/Te interdiffusion, CdSe in the Se bilayer configuration was unable to form an n-type emitter layer in processed devices. In situ As doping of the Cd(Se,Te) layer benefited the device junction quality with current density reaching 28.3 mA/cm 2 . The results provide useful insights for the optimisation of Cd(Se,Te)/CdTe solar cells. Compositional control of optical band gap in Cd(Se,Te) thin films (0 ≤ x ≤ 1) (left) and the Se profile in finished Cd(Se,Te) devices (right) fabricated by MOCVD. • Cd(Se,Te) thin films (0 ≤ x ≤ 1) deposited with linear compositional control using a chamber-less MOCVD process. • CdSe-only and CdSe/CdSe 0.2 Te 0.8 bilayers utilised for Cd(Se,Te) grading in devices. • In-situ and ex-situ group V (arsenic) doping of the graded Cd(Se,Te) obtained. • Device performance improved for thinner CdSe layers and in-situ doped bilayers. • Good control of Se profile achieved via CdSe and CdSe/CdSe 0.2 Te 0.8 properties.

Synthesis, Characterization and Optoelectronic Properties of Solar Cells Device for Vacuum Thermally Evaporated Pure and Gallium Doped CdSe Thin Films

Heterojunctions n-CdSe/p-Si, n-CdSe/P-Si and CdSe:Ga/p-Si have, through thermal evaporation, been based on P-type Si (002). Thin films with different doping ratios of 1, 3 and 5 wt percent are made. For the purpose of achieving optimal conditions the electrical and photovoltaic aspects of these films have been established. Solar cell quality is graduated. They were made of a vacuum heat evaporated mixture of CdSe and ga atoms to create a thin, p-Si single wafer film with a thickness of 3.5 μm and resistivity of 0.78-1.5 Ohm-cm-2 on R.T. They are then formed by n-CdSe/p-Si and n-Cdse(Ga)/p-Si heterojunctions. The density of the existing short circuit (jsc, open-circuit (Voc/fill factor (ff)) and conversion rate of 40 mW/cm2 (AM1) intensity. The efficiency of solar cells is calculated prior to and after a Ga dopant. The aim of this analysis was to determine characterization and optoelectronic characteristics of CdSe pure and gallium-doped solar cells in thin films. The result of this analysis under dark I-V conditions show good disciplinary behavior and an exponential relationship to the potential present bias. The calculation of the C-V suggested an abrupt form of heterozone diodes. The built-in potential Vbi is calculated and is found increasing after Ga-doping process. The built-in potential and the depletion width increases with increasing of Ga doping ratio. Solar cell conversion efficiency of n-CdSe/p-Si and n-CdSe:Ga/p-Si heterojunction properties were studied is found to be 5.25 % at 5 Wt% of Ga doping ratio. In conclusions, The I-V characteristic of Ga-doped CdSe solar cell thin film under the illumination conditions gives conversion efficiency of 5.25% at doping ratio 5%. This result of conversion is directly proportional to the Ga concentrations.

Influence of Ni-Co dual doping on structural and optical properties of CdSe thin films prepared by chemical bath deposition method

Pure and Ni-Co dual doped CdSe thin films were deposited on glass substrate by chemical bath deposition (CBD) technique. The deposited thin films were annealed for 1 h at 500 °C. X-ray diffraction (XRD) and UV–vis Spectroscopy were used to study the structural and optical properties of the prepared thin films. XRD studies revealed the hexagonal phase for pure CdSe, CdSe: 0%Ni-8%Co, CdSe: 2%Ni-6%Co, CdSe: 6%Ni-2%Co and CdSe: 8%Ni-0%Co thin films, while CdSe: 4%Ni-4%Co produced the cubic phase. The XRD results revealed that the dual doping affected strongly the preferred orientation of the crystallites. The optical band gap energy, Urbach energy, Extinction coefficient, refractive index, real and imaginary dielectric constants and optical conductivity were calculated for all obtained thin films. The direct optical band gap energy of pure CdSe film was 1.43 eV and it decreased with Ni and Co dual doping. The lowest optical band gap energy was observed for CdSe: 4%Ni-4%Co. The dual doping with Ni and Co increased the efficiency of CdSe thin films to be used as solar cells.

Intense photoluminescence from Cu-doped CdSe nanotetrapods triggered by ultrafast hole capture.

Brightly photoluminescent Cu-doped CdSe nanotetrapods (NTPs) have been prepared by a modified hot injection method. Their photoluminescence (PL) has a quantum yield of 38% and decays slowly over a few microseconds, while the PL in undoped NTPs has a rather small quantum yield of 1.7% and decays predominantly in tens of picoseconds, with a minor component in the nanosecond time regime. PL spectra of doped NTPs are significantly Stokes shifted compared to the band edge (BE). Efficient PL quenching by a hole scavenger confirms the oxidation state of +I for the dopant ion and establishes hole capture by this ion to be the primary event that leads to the Stokes shifted PL. A fast decay of the photoinduced absorption band, along with a similar decay in PL, observed in a femtosecond optical gating experiment, yields a time constant of about a picosecond for the hole capture from the valence band (VB) by Cu+. The remarkably long PL lifetime in the doped NTPs is ascribed to the decrease in the overlap between the wavefunctions of the photogenerated electrons and the captured hole. Hot carrier relaxation processes, triggered by excitation at energies greater than the band gap, leave their signature in a rise time of few hundreds of femtoseconds, in the ground state bleach recovery kinetics. Hence, a complete picture of exciton dynamics in the doped NTPs has been obtained using ultrafast spectroscopic techniques working in tandem.

Quantum dot sensitized solar cell based on the different photoelectrodes for the enhanced performance

In this work, the TiO2 nanoparticles have been used for the fabrication of CdS/TiO2, CdSe/TiO2, ZnS/CdSe/CdS/TiO2, ZnS/CdSe:Cu/CdS/TiO2 and ZnS/CdSe:Mn/CdS/TiO2 quantum dot-sensitized solar cells. The TiO2 films are sensitized with consecutive layers of CdS, CdSe quantum dots. Further, Cu2+ or Mn2+ ions were doped on CdSe quantum dots by successive ion layer adsorption and reaction. The performance of the QDSSCs is examined in detail using polysulfide electrolyte with Cu2S counter electrode. The cells containing CdSe quantum dots doped with the these ions show an improved short circuit current density (∼20.01 mA/cm2) with a maximum power conversion efficiency of 4.31% under 1 sun illumination. This enhancement is mainly attributed due to the superior light harvesting ability of the CdSe:Cu or CdSe:Mn quantum dots and make large accumulation of photo-injected electrons in the conduction band of TiO2 nanoparticles. In addition, the combination of doped CdSe and the presence of CdS layers caused lower recombination of photo-injected electrons with the electrolyte. These changes are demonstrated in this studying by using photovoltaic and electrochemical impedance spectroscopy.

A photoelectrochemical sensor for highly sensitive detection of amyloid beta based on sensitization of Mn:CdSe to Bi2WO6/CdS

A high sensitivity photoelectrochemical (PEC) immunosensor for amyloid beta (Aβ) detection, which has great neurotoxic effect on the progression of Alzheimer's disease (AD), was presented based on the sensitization of Mn2+ doped CdSe (Mn:CdSe) to Bi2WO6/CdS electrode. Bi2WO6 was synthesized successfully with a unique flower-like amorphous structure, providing a merit to load functional CdS for obtaining an expected PEC response. Mn:CdSe was used to label Aβ for acquiring Mn:CdSe-Aβ bioconjugate and enhancing the detection sensitivity via the competitive immunoreaction of Mn:CdSe-Aβ and Aβ with antibody immobilized on Bi2WO6/CdS electrode. The doped of Mn2+ in CdSe nanoparticles could induce energy defect that impeded the recombination of photo-generated charges, and greatly enhanced PEC response for ultrasensitive detection of Aβ. The proposed immunosensor for Aβ showed a linear range of 0.2 pg mL−1–50 ng mL−1 with a detection limit of 0.068 pg mL−1, also with good stability, high selectivity, and acceptable reproducibility. The sensitization of Mn:CdSe provided a new way for preparation of highly sensitive protein biosensors.

Ultrafast Carrier Dynamics of Photo-Induced Cu-Doped CdSe Nanocrystals

The understanding of ultrafast carrier relaxation process in doped semiconductor quantum dots (QDs) is very important for their potential applications in light-emitting diodes, optoelectronics. Here, we have studied the change in electronic properties of Cu-doped CdSe QDs upon light illumination. The light-induced effect leads to the enhancement of the band edge decay time and reduces the decay time of the dopant emission due to photocorrosion of Cu-doped CdSe QDs. The bleaching recovery kinetics and the hot electron cooling dynamics have been studied by using femtosecond transient absorption spectroscopy. It is observed that the electron cooling process of doped CdSe QDs is dependent on the dopant concentration and the cooling kinetics of doped CdSe QDs are found to be slower than undoped QDs. After light irradiation, the cooling processes of hot electron and recovery process in doped systems are modified.

A comparative study of transport properties of copper doped cadmium selenide thin films at two dopant concentrations

We have explored the effect of Cu dopant concentration on the electrical transport properties of Cu doped CdSe thin films at two concentrations of Cu (at 1 and 5 at.%). Structural, morphological and elemental analysis has been carried out by using X-ray Diffraction (XRD), Scanning electron microscopy (SEM) and Energy Dispersive X-ray analysis (EDX). XRD analysis reveals the hexagonal (wurtzite) structure of nc-CdSe:Cu 1% and nc-CdSe:Cu 5% thin films. EDX analysis determines the atomic weight percentage of Cu in these thin films. SEM studies reveal that the grains are uniformly distributed all over the surface of the substrates for nc-CdSe:Cu 1% and nc-CdSe:Cu 5% thin films. Dark conductivity measurements are made on nc-CdSe:Cu 1% and nc-CdSe:Cu 5% thin films in the temperature range 110–370 K in order to determine the effect of Cu concentration. The obtained results reveal that dark conductivity increases as the Cu dopant concentration increases as compared to undoped nc-CdSe thin films. Dark conductivity graphs show two distinct regions at high and low temperatures with decreasing activation energies. Low temperature data is analyzed using Mott’s variable-range hopping model which indicates hopping in localized states near the Fermi level. Various Mott parameters such as the density of localized states N(EF), characteristic temperature (To), hopping distance (R) and hopping energy (W) near the Fermi level are calculated. The concentration of charge carriers and carrier mobility are calculated for nc-CdSe:Cu 1% and nc-CdSe:Cu 5% thin films by using Hall measurements. Constant photocurrent measurement is also performed on Cu 1% and Cu 5% doped CdSe thin films to determine occupied density of states, Urbach parameter and density of defect states. Obtained results show that occupied density of states increases for nc-CdSe:Cu 5% as compared to nc-CdSe:Cu 1% thin films.

STRUCTURAL AND THERMAL STUDY OF RUTHENIUM AND INDIUM DOPED CDSE THIN FILMS

STRUCTURAL AND THERMAL STUDY OF RUTHENIUM AND INDIUM DOPED CDSE THIN FILMS

Symmetry Breaking Induced Activation of Nanocrystal Optical Transitions

ABSTRACTWe have analysed the effect of symmetry breaking on the optical properties of semiconductor nanocrystals due to doping by charged impurities. Using doped CdSe nanocrystals as an example, we show the effects of a Coulomb center on the exciton fine-structure and optical selection rules using symmetry theory and then quantify the effect of symmetry breaking on the exciton fine structure, modelling the charged center using a multipole expansion. The model shows that the presence of a Coulomb center breaks the nanocrystal symmetry and affects its optical properties through mixing and shifting of the hole spin and parity sublevels. This symmetry breaking, particularly for positively charged centers, shortens the radiative lifetime of CdSe nanocrystals even at room temperature, in qualitative agreement with the increase in PL efficiency observed in CdSe nanocrystals doped with positive Ag charge centers [A. Sahu et.al., Nano Lett. 12, 2587, (2012)]. The effect of the charged center on the photoluminescence and the absorption spectra is shown, with and without the presence of compensating charges on the nanocrystal surface. While spectra of individual nanocrystals are expected to shift and broaden with the introduction of a charged center, configuration averaging and inhomogeneous broadening are shown to wash out these effects. The presence of compensating charges at the NC surface also serves to stabilize the band edge transition energies relative to NCs with no charge centers.

RETRACTED: Near-infrared-to-visible upconverting luminescence of Er3+-doped CdSe nanocrystals grown by chemical bath

Abstract CdSe thin films were prepared by chemical bath and doped in situ with Er3+ ions. Three impurity levels were prepared by changing the relative volume of the salt solution containing Er3+ ions in the CdSe growing solution. Changes in the grain size (∼5.5–3.5 nm) and band gap energy (∼1.80–2.25 eV) were observed in the undoped and doped CdSe films, respectively. Photoluminescence studies displayed room temperature emission exhibiting NIR-to visible upconversion. The transition bands 4I13/2 → 4I15/2, 2I9/2 → 4I15/2 and 2F9/2 → 4F15/2 in the ∼700–850 nm region were investigated. Upconversion emissions were observed from the CdSeEr sample under light excitation (325 nm). The upconversion emission intensity ratio of these transitions is attributed to the variation of the local structure around Er3+ ions. These results confirm that visible upconversion emissions of Er3+ in the CdSeEr nanocrystals are mainly produced via two-photon excited-state absorption and energy transfer upconversion processes.

High performance of Mn-doped CdSe quantum dot sensitized solar cells based on the vertical ZnO nanorod arrays

Abstract Doping transition metal ions Mn2+ to semiconductor quantum dots (QDs) are extremely interesting for the development of photovoltaic devices. Quantum dot sensitized solar cells (QDSCs) are able to show promising power conversion efficiencies (PCE) by employing Mn2+ doped QDs. Herein we achieve effective CdS/Mn CdSe/ZnS QDs co-sensitized vertical ZnO nanorod arrays film that provides an appreciable enhancement in photovoltaic performance. The measured PCE of the solar cells with Mn2+ doped CdSe QDs is 4.14%, which is higher than the efficiency of 2.91% for the solar cells without Mn2+ or a ∼42% increase. The improvement in PCE is ascribed to a higher open-circuit voltage (Voc = 0.74 V) and a superior short-circuit current density (Jsc = 12.6 mA cm−2) with the introduction of Mn2+ into CdSe QDs. The enhancement seen with Mn2+ doped CdSe QDs are investigated and explained by the fact that the enhanced light absorption and reduced charge recombination by the formation of Mn CdSe passivation layer covering the QDs.