Doped CdTe Research Articles

Advancement in CdMnTe-based photovoltaic cells: Grain growth, deep states and device efficiency assessment with chlorine treatment

The suitability of the metal rear contact, the density of surface states, the rate of recombination of the absorber layer, and open circuit voltage loss are all innate issues with typical CdTe solar cells. These problems can be addressed with small Mn doping in CdTe, making it a Cd1-xMnxTe (CMT) trinary semiconductor, which can tune the band gaps. With the purpose of give an alternative to traditional CdTe material, CMT PV cells having device structures of ITO/CdS/CMT/Au have been investigated in this study with CdCl2 treatment. The devices were fabricated by vacuum evaporation, and CMT PV cells without and with CdCl2 treatment demonstrated the efficiency of 7.83% and 8.76%. The capacitance–voltage data were also used to calculate the doping concentration and depletion layer width, while deep trap states in the devices were analyzed with the help of Mott-Schottky plots. The Quantum efficiency measurements were done at zero bias to identify the optical or electronic losses in devices with CdCl2 treatment. The grain growth was also explored with chlorine treatment by analyzing SEM images. For further improve the device performance, the states responsible for recombination must be located and eliminated to enhance the fill factor and efficiencies of the devices. The devices' repeatability was also examined and was found to be satisfactory with a 6–10% deviance. This work demonstrates the need for additional research to enhance the performance of CMT PV cells with CdCl2 treatment for usage as an affordable alternative photovoltaic source.

Arsenic doping and diffusion in CdTe: a DFT study of bulk and grain boundaries

The doping of CdTe with As is a method which is thought to increase cell efficiency by increasing electron hole concentrations. This doping relies on the diffusion of As through CdTe resulting in AsTe substitution. The potential effectiveness of this is considered through kinetic and electronic properties calculations in both bulk and Σ3 and Σ9 grain boundaries using Density Functional Theory. In bulk zinc-blende CdTe, isolated As diffuses with barriers <0.5 eV and with similar barriers through wurtzite structured CdTe, generated by stacking faults, suggesting that As will not be trapped at the stacking faults and hence the transport of isolated As will be unhindered in bulk CdTe. Substitutional arsenic in bulk CdTe has little effect on the band gap except when it is positively charged in the AX-centre position or occurring as a di-interstitial. However in contrast to the case of chlorine, arsenic present in the grain boundaries introduces defect states into the band gap. This suggests that a doping strategy whereby the grain boundaries are first saturated with chlorine, before single arsenic atoms are introduced, might be more beneficial.

Quantitative analysis of Cu XANES spectra using linear combination fitting of binary mixtures simulated by FEFF9

X-ray absorption near edge structure (XANES) is a powerful tool to probe the fingerprint of local structures, and when coupled with X-ray microscopy, the small spot size enables one to probe very specific regions of interest in a device or material, e.g. interfaces/bulk, different grains, good/bad electrical areas. In this work, we investigate the use of linear combination fitting (LCF) of XANES spectra for the particular case of Cu doping in CdTe. We show that the experimental data seem to be accurately represented by standards of Cu2Te and its substoichiometric counterpart, Cu1.43Te. We use Cu in CdTe as a case study to evaluate the accuracy of linear combination fitting using simulated standards, given that experimental standards for certain phases (e.g. Cu1.43Te) or defect structures (e.g. vacancies) cannot be readily obtained. We discuss how spectral features of the FEFF9-simulated standards, fitting ranges, and noise levels all dictate the accuracy of this type of analysis. We show that the greater the spectral difference between the two standards, the better the LCF is able to differentiate between the two structures and to tolerate experimental noise. Finally, we estimate the error of the fitted weights for different spectral features and noise levels and propose a framework to study local structures semi-quantitatively by using binary mixtures of FEFF9-simulated standards.

In/CdTe/Au p–n junction-diode X/[formula omitted]-ray detectors formed by frontside laser irradiation doping

The fabricated In/p-CdTe/Au diode structures with Schottky (In/p-CdTe) and quasi-ohmic (Au/p-CdTe) contacts were transformed into p–n junction diodes by applying the developed frontside laser irradiation doping technique. The Schottky diodes with In and Au electrodes (both with thickness of 400 nm), deposited on the chemically pre-treated B- and A-face of the detector-grade CdTe(111) single crystals, respectively, were subjected to multiple (from tens to thousands times) irradiation from the In film side with series of nanosecond pulses of a KrF excimer laser. As a result of such irradiation, a thin heavily doped n-type CdTe:In layer was formed, a shallow abrupt p–n junction was created and thus the In/CdTe/Au Schottky diode was transformed into the In/CdTe/Au p–n junction diode. The temperature distributions in the In/CdTe/Au structure under laser irradiation were calculated and the I–V characteristics of the diodes were measured for different energy densities E and number N of laser pulses, respectively. The processes of frontside laser irradiation doping and carrier charge transport mechanisms in the created In/CdTe/Au p–n junction diodes were discussed. The samples with higher performance were obtained when only a part of the In electrode thickness was melted during a single laser action (E∼110 mJ/cm 2) and repeated (N∼300–500) irradiation was employed. The fabricated In/CdTe/Au p–n junction-diode structures with relative low reverse dark currents (∼20–50 nA/cm2) were quite sensitive to X/γ-rays and demonstrated sufficient ability to detect the emission of 241Am, 57Co, and 137Cs isotopes. It has been shown that applying the frontside laser irradiation doping technique to In/CdTe/Au structures, it is possible to transform Schottky diodes with low characteristics into highly rectifying In/CdTe/Au p–n junction diodes which are X/γ-ray detectors with moderate or even high detection parameters.

Structural, Optical, and Magnetic Properties of Gd Doped CdTe Quantum Dots for Magnetic Imaging Applications

Induced room-temperature ferromagnetic behavior (RT-MF) of Gd doped CdTe (GDC) quantum dots (QDs) is reported. Pure CdTe QDs were synthesized by colloidal route using thiol stabilizers in an aqueous medium. The magnetic moments were induced by the inclusion of Gd in CdTe QDs. The effect of Gd ion substitution in CdTe lattices was characterized by X-ray diffraction which confirmed the formation of cubic zinc blende structure. The optical response of the prepared QDs was studied via UV–vis absorption spectroscopy, which indicated that Gd ion substitution alters the optical response toward a longer wavelength; this is further confirmed by corresponding emission analysis through Fluorescence emission spectroscopy. Quantum yield measurements confirmed that the GDC QDs give better quantum yield than pure CdTe QDs through the substitution of Gd ions. The formation of CdTe QDs with Gd ion substitution was confirmed by binding energy analysis through X-ray photoelectron spectroscopy. RT-MF of GDC QDs was revealed by vibrating-sample magnetometer measurement. Hence, the prepared GDC QDs were determined to be a vital DMS material for room-temperature spintronics applications.

Effects of co-doping in semiconductors: CdTe

Co-doping is an important method to improve doping properties in semiconductors, which is expected to lower the defect formation energy through the Coulomb interaction or covalent coupling between co-dopants and reduce the transition energy level through the level repulsions. However, the effectiveness of co-doping is sensitive to the type of co-dopants, and in some cases, negative effects can exist. Here, using $p$-type doping in CdTe as an example, we systematically investigate different dopant combinations based on first-principles hybrid functional calculations. We show that the complex of one donor + one double acceptor, e.g., ${\mathrm{Cl}}_{\mathrm{Te}}+{\mathrm{V}}_{\mathrm{Cd}}$, can cause a decrease in defect formation energy and a reduction in acceptor level, thus improving the dopability, especially when the Cl treatment is done at low temperature. The combination of two acceptors + one donor, e.g., ${\mathrm{Cl}}_{\mathrm{Te}}+2{\mathrm{Cu}}_{\mathrm{Cd}}$, has little or even negative effects because of the coexistence of the acceptor-acceptor and donor-acceptor coupling. More importantly, we show that the combination of one deep acceptor + one shallow acceptor, e.g., ${\mathrm{Sb}}_{\mathrm{Te}}+{\mathrm{P}}_{\mathrm{Te}}$, produces a much deeper acceptor level because the nominal deep acceptor ${\mathrm{Sb}}_{\mathrm{Te}}$ acts as a donor with respect to the shallow one, and then the deep acceptor state will be pushed even deeper due to the level repulsion. Thus, we should avoid this type of acceptor-acceptor co-doping to achieve high hole concentration. Our general understanding of the co-doping approach, therefore, provides a guideline for the future design of shallow defect complexes in CdTe and other semiconductors.

Excitation-density and excess-energy dependence of ultrafast dynamics of photoexcited carriers in intrinsic bulk CdTe

In this study, ultrafast dynamics of photoexcited carriers in an intrinsic CdTe film are investigated deeply and systematically as a function of carrier density and excess energy using femtosecond-resolved pump–probe transient differential transmission spectroscopy. A dynamic model is developed based on an interband transition absorption model in direct bandgap semiconductors by introducing the dynamics of thermalization, cooling and recombination of photoexcited carriers into the interband transition absorption model. Then, the model is used to best fit the measured ultrafast dynamics to retrieve the initial temperature of thermalized electrons and time constants of the thermalization, cooling and recombination dynamic processes as a function of carrier density and excess energy. The increase with carrier density and the decrease with excess energy of thermalization time constant reveal that thermalization process of photoexcited carriers is dominated by carrier-phonon scatterings. We find for the first time that cooling of thermalized carriers depend strongly on carrier density and excess energy, and cooling time constant varies in a wide range from 0.2 to 5 ps. It is also found that carrier recombination in the intrinsic CdTe film is dominated by the radiative recombination of electron-hole pairs, rather than Auger recombination as reported in doped CdTe films. These new results are very important to understanding of microscopic mechanism of relaxation processes of photoexcited carriers and applications of CdTe-based optoelectronic devices.

Computational design of passivants for CdTe grain boundaries

CdTe is the second most-widely deployed photovoltaic (PV) material due to its high efficiency and low manufacturing costs. Currently, polycrystalline CdTe (poly-CdTe) has a record efficiency of ~22%, which is still well below the theoretical limit (~30%). Polycrystalline CdTe films that have incorporated Cl or Se show higher efficiency, possibly due to the segregation of these ions to the grain boundaries (GBs), where they may passivate the dangling bonds. However, the efficiency enhancement mechanisms of passivants in CdTe GBs, and the feasibility of employing alternative passivants, have not been well explored. Here, we present a systematic computational study of CdTe GBs with potential passivants, namely S, P, As, Se, and Sb on Te sites, and Na, Mg, Al, Sc, Cu, and Zn on Cd sites. Density functional theory (DFT) calculations were performed on GB dislocation core structures derived from scanning transmission electron microscopy (STEM) images of a model GB (bicrystal). We computed the segregation thermodynamics, electronic density of states, and charge variations near doped CdTe GBs. We find that segregation of impurities to GBs is thermodynamically favorable. For a Te-terminated core, Se, S, and P on Te sites effectively reduce midgap states. For both Cd- and Te- terminated dislocation cores, Sc and Al reduce midgap states when substituted for Cd atoms. The greatest improvement was achieved with co-doping, i.e. simultaneously substituting Te with Se and substituting Cd with Cu or Al. The elimination of midgap states is predicted to increase the photovoltaic efficiency of CdTe by reducing the recombination at grain boundaries. • CdTe solar cell efficiency depends highly on grain boundary properties. • Large scale first principles computational study was performed on realistic grain boundary models. • For a Te-terminated core, Se, S, P, and As on Te sites effectively reduce midgap states and improve efficiency. • For both Cd- and Te- terminated dislocation cores, Sc and Al on Cd sites reduce the midgap states and improve efficiency.

Numerical approach to optimizing the doping concentration of the absorber layer to enhance the performance of a CdTe solar cell

Cadmium telluride (CdTe)-based solar cells have been proving their potential for high efficiency performance for several decades. However, efficient p-type doping of CdTe has remained a critical challenge for decades thus limiting the performance of this type of solar cell. Thus, this work intends to assess the effects of various dopants and their optimization in order to obtain efficient photovoltaic (PV) performances. In the process we used numerical simulation software SCAPS-1D as it expedites and facilitates the modeling of a solar cell through optimizations and variations. The studied CdTe solar cell structure comprises multi-junction semiconductor layers such as n-ITO/n-ZnO/n-CdS/p-CdTe in a superstrate structure. Three different types of absorber layer dopants such as copper (Cu), silver (Ag) and arsenic (As) are used, respectively. The work started with the optimization of carrier concentration followed by the variation of the thickness of the absorber layer. The PV performances in terms of open-circuit voltage, short-circuit current density, fill factor and efficiency are presented and, after comparison, the As dopant is shown to be a promising candidate. Also, the working temperature is varied to obtain a suitable environment under which the solar cell can work efficiently.

Bismuth Doping of CdTe: The Effect of Spin–Orbit Coupling

Using the Heyd, Scuseria, and Ernzerhof (HSE) hybrid functional, with the range‐separation parameter modified to match the CdTe bandgap, the electronic structure and thermodynamic properties of bismuth‐doped CdTe are calculated. The energy levels associated with bismuth in CdTe bandgap can be obtained only when the spin–orbit coupling (SOC) is included. Substitutional and interstitial Bi atom positions in CdTe lattice are investigated. Contrary to the outcome of calculations without SOC, these simple defects generate bands inside the CdTe bandgap. These bands can act as intermediate steps in two‐step light absorption processes that lead to increasing the photocurrent in the solar cell.

The optical performance of Cd1 − xTmxTe (0 ≤ x≤ 0.07) QDs synthesized via s,s′-phenylenebis-ethynediyl-phenylene-bisthioacetate assisted microwave approach for laser devices

Here, we have developed a new series of quantum dots based on the incorporation of thulium, Tm, atoms as efficient dopant in the cubic CdTe crystal structure for laser diode application potential. Therefore, Cd1 − xTmxTe (0 ≤ x ≤ 0.07) quantum dots were synthesized using s,s′-phenylenebis-ethynediyl-phenylene-bisthioacetate assisted microwave approach. The measurements of X-ray diffractions implied the preservation of the cubic phase of the CdTe crystals at all Tm dopant contents. The transmission electron microscopy inspected the formation of monodisperse and self-assemble nanoparticles with mean diameter from 1.8 ± 0.2 nm to 5.7 ± 0.3 nm, depending on the amount of Tm incorporated in the CdTe nanocrystals. A modulation of the optical bandgap was observed because of the doping of CdTe with Tm atoms. Highly luminescent emission spectra with tunable colors were obtained. The emission spectra showed sharp intense emitted light with an enhancement of its intensity reached to seven folds compared with the un-doped CdTe crystals. An increasing of quantum yields from 31% to 94% was realized. A decrease of the Stokes shift was observed which implies the synthesis of Cd1 − x TmxTe QDs free of defects for the first time. This unique performance renders the prepared Cd1 − x TmxTe to be potential candidate for the manufacturing of laser diodes.

One pot synthesis of highly luminescent Cd1-xOsxTe (0 ≤ x ≤ 0.1) nanocrystals synthesized via poly(9,9-dioctylfluorene-alt-benzothiadiazole) assisted polyol approach

Here, we report for the first time the creation of Cd1-xOsxTe (0 ≤ x ≤ 0.1) quantum dot using poly(9,9-dioctylfluorene-alt-benzothiadiazole) assisted polyol approach. The stimulus of osmium, Os, on the structure and optical emission behavior of CdTe quantum dots were examined. The X-ray diffraction measurement revealed the preservation of the cubic structures of CdTe crystals at all Os atoms concentration, implies the successful partial replacement of the Os atoms in the Cd cites. The transmission electron microscopy inspected that the doping of CdTe with Os atoms caused an increase of its particle diameter from 1.9 ± 0.2 nm to 7.1 ± 0.3 nm. The inclusion of Os atoms in the Cd atom cites instigated a shift to the red spectrum for both of the optical absorption/emission spectra. Astonishing upgrading of the luminescent intensities and a reduction of the width of emission spectra was achieved. An enlargement of the luminescent quantum yield from 31 % to 92 % was perfectly accomplished. A decreasing of the Stokes shift owing to the inclusion of Os atoms in the Cd cites, thereby a successful constraining of the crystal defects was realized. These outstanding demeanors may concrete an avenue to utilizing the developed Cd1-xOsxTe semiconductor quantum dots for the fabrication of competent laser diodes.

Semiconductor CdTe-Doped CdO Thin Films: Impact of Hydrogenation on the Optoelectronic Properties

Doping or incorporation with exotic elements are two manners to regulate the optoelectronic properties of transparent conducting (TCO) cadmium oxide (CdO). Nevertheless, the method of doping host CdO by CdTe semiconductor is of high importance. The structural, optical, and electrical properties of CdTe-doped CdO films are studied for the sake of promoting their conducting parameters (CPs), including their conductivity, carrier concentration, and carrier mobility, along with transparency in the NIR spectral region; these are then compared with the influence of doping the host CdO by pure Te ions. X-ray fluorescence (XRF), X-ray diffraction (XRD), optical absorption spectroscopy, and electrical measurements are used to characterise the deposited films prepared by thermal evaporation. Numerous results are presented and discussed in this work; among these results, the optical properties are studied through a merging of concurrent BGN (redshift) and BGW (blue shift) effects as a consequence of doping processes. The impact of hydrogenation on the characterisations of the prepared films is investigated; it has no qualitative effect on the crystalline structure. However, it is found that TCO-CPs are improved by the process of CdTe doping followed by hydrogenation. The utmost TCO-CP improvements are found with host CdO film including ~ 1 %Te, in which the resistivity decreases by ~ 750 %, carrier concentration increases by 355 %, and mobility increases by ~ 90% due to the increase of Ncarr. The improvement of TCO-CPs by hydrogenation is attributed to the creation of O-vacancies because of H2 molecule dissociation in the presence of Te ions. These results reflect the potential of using semiconductor CdTe -doped CdO thin films in TCO applications. Nevertheless, improvements of the host CdO CPs with CdTe dopant are of a lesser degree compared with the case of doping the host CdO with pure Te ions.

Magnetism in d0 impurities doped CdTe: ab-initio calculations

In this work, using the ab-initio calculations, we have investigated the phantom magnetism when the diamagnetic solids, carbon and nitrogen with $$d^{0}$$ doped CdTe. We have applied in these calculations the combination between the Korringa–Kohn–Rostoker and coherent potential approximation method within the local density approximation and generalized gradient approximation (GGA). In this study, the doped compound presents a metallic behavior for both the approximations characterized by a small moment of about 0.299/0.326 and 0.249/0.266 $$\mu _{{\mathrm{B}}}$$ for 24% of C and N, respectively. The polarization has shown a low and decreasing value from 43.73/59.56 to 0.29/2.26% for 9% and 24% of C impurity concentration, respectively. Unlike for the case of N, this parameter varies from 76.7/72.86 to 85.29/83.63% for 9% and 24% concentration, respectively. In addition, we have determined the mechanism of ferromagnetic coupling for the C- and N-doped CdTe. Furthermore, the stability of the compound is investigated by comparing the energy difference between the spin glass and ferromagnetic states. It is found that below the percolation threshold, contrary to the case of doping by N except for 20% using GGA, the C impurities lead to the most ferromagnetic stable phase. While the system changes its stability above this threshold when doped by the C impurities. Finally, we have estimated and discussed the Curie temperature using the mean field approximation.

Optimization and comparative evaluation of optoelectronic properties of hydrothermally synthesized CdIn2Te4 thin films: PEC performance

Herein, hydrothermal route was directly employed to synthesize Indium doped CdTe nanocrystalline thin films. The influence of In doping on the optical, structural, morphological and photoelectrochemical solar cell properties have been investigated. The optical absorption study illustrates that, maximum absorption was observed in between 500–700 nm with decrease in band gap energy from 1.47 to 1.35 eV as function of In doping. Structural analysis reveals that, transition in crystal structure from hexagonal to tetragonal on In doping in CdTe. Morphological analysis demonstrates that, evolution of 1-D nanowire like morphology in CdIn2Te4 thin film. Compositional analysis confirms the presence of Cd, In and Te elements in CdIn2Te4 thin film with stoichiometric atomic percentage. X-ray photoelectron spectroscopy (XPS) analysis confirms that, presence of Cd, In and Te ions in its valence states of Cd2+, In3+ and Te2− respectively. Current density-voltage measurement illustrates that, CdIn2Te4 photocathode shows improved PEC performance with photoconversion efficiency 2.84%. The improved photovoltaic performance of In doped CdTe photocathode was explained in detail with the help of Nyquist plots and corresponding circuit model of the electron impedance spectra.

Investigations of rare earth doped CdTe QDs as sensitizers for quantum dots sensitized solar cells

Gd doped CdTe (Gd:CdTe) QDs sensitized working electrodes were fabricated for QDSSC applications. In this fabrication process, mercapto succinic acid capped Gd:CdTe QDs were synthesized by colloidal method and used as the sensitizer. Improved optical properties of the prepared QDs were examined by optical absorption and emission spectral analysis. Fluorescence quantum yield measurement reveals that 10% Gd:CdTe QDs shows the highest quantum yield of 67%. XRD analysis confirms the cubic zinc blende crystalline structure of the prepared QDs and the dopant concentration dependent cell parameters and crystallite sizes were revealed. Performance of capping molecules over the prepared QDs was analyzed by FT-IR studies. Enhanced photovoltaic performance of prepared pure and doped QDs was analyzed through J-V characteristic curves, which show better photovoltaic response with an efficiency of 2.24% for 10% Gd:CdTe QDs.

Incorporation and activation of arsenic in single-crystal CdTe layers grown by metalorganic chemical vapor deposition

The electrical properties of arsenic doped CdTe epitaxial layers grown on GaAs (100) substrates by metalorganic chemical vapor deposition with dimethylcadmium and diethyltellurium are investigated. Tris(dimethylamino)arsine was used as the arsenic source. CdTe layers with arsenic concentration from 1.6·1017 cm−3 to 1.5·1018 cm−3 were obtained by varying only diethyltellurium/dimethylcadmium mole ratio from 6.2 to 0.5. The as-grown CdTe:As layers had p-type conductivity with hole concentration about 2·1015 cm−3 within diethyltellurium/dimethylcadmium mole ratio 1–6.2 and n-type at diethyltellurium/dimethylcadmium = 0.5. Post-growth annealing (250–500 °C) were used to increase the activation efficiency of arsenic. The highest hole concentration was 2.1·1017 cm−3 at arsenic concentration of 4.5·1017 cm−3, but the maximum activation efficiency approximately of 85% was achieved at lower concentration levels. The ionization energy of AsTe acceptor determined from temperature-dependent Hall measurements was in the range of 96–112 meV. Low-temperature photoluminescence emission spectra of arsenic doped CdTe layers showed a peak at ~1.51 eV which is associated with AsTe acceptor with ionization energy about 90 meV. Possible mechanisms of arsenic compensation in CdTe by intrinsic defects and the AX-centers formation are discussed.

Optical and electrical design guidelines for ZnO/CdS nanorod-based CdTe solar cells.

An alternative structure to planar CdTe solar cells is realized by coating ZnO/CdS nanorods (NRs) with a CdTe layer. These structures are expected to achieve high-powered conversion efficiencies through enhanced light absorption and charge carrier collection. ZnO NR-based CdTe solar cell efficiencies; however, they have remained well below their planar counterparts, thus hindering NRs in CdTe solar cells' advantages. Here, we analyze the light trapping and carrier collection efficiencies in two types of ZnO NR-based CdTe solar cells through optical and electrical simulations. The buried CdTe solar cells are formed by completely filling the gaps in between ZnO/CdS NRs. This produces a maximum achievable photo-current of 27.4 mA/cm2 when 2000 nm-tall and 20̊-angularly-deviated NRs are used. A short-circuit current density of 27.3 mA/cm2 is achievable with the same geometry for 5 rods/μm2-dense NRs when a moderate CdTe doping density and a CdS/CdTe surface velocity of 1016 cm-3 and 104 cm/s are used, respectively. We reveal the potential of buried CdTe solar cell for high-charge carrier collection and provide a design guideline in order to achieve high short-circuit current densities with ZnO NR-based CdTe solar cells.

Study of thin film poly-crystalline CdTe solar cells presenting high acceptor concentrations achieved by in-situ arsenic doping

Doping of CdTe using Group-V elements (As, P, and Sb) has gained interest in pursuit of increasing the cell voltage of CdTe thin film solar devices. Studies on bulk CdTe crystals have shown that much higher acceptor concentration than the traditional copper treatment is possible with As, P or Sb, enabled by high process temperature and/or rapid thermal quenching under Cd overpressure. We report a comprehensive study on in-situ As doping of poly-crystalline CdTe solar cells by MOCVD, whereby high acceptor densities, approaching 3 × 1016 cm−3 were achieved at low growth temperature of 390 °C. No As segregation could be detected at grain boundaries, even for 1019 As cm−3. A shallow acceptor level (+0.1 eV) due to AsTe substitutional doping and deep-level defects were observed at elevated As concentrations. Devices with variable As doping were analysed. Narrowing of the depletion layer, enhancement of bulk recombination, and reduction in device current and red response, albeit a small near infrared gain due to optical gap reduction, were observed at high concentrations. Device modelling indicated that the properties of the n-type window layer and associated interfacial recombination velocity are highly critical when the absorber doping is relatively high, demonstrating a route for obtaining high cell voltage.

Photovoltaic Performances of Yb Doped CdTe QDs Sensitized TiO2 Photoanodes for Solar cell Applications

In this work, Yb doped CdTe QDs sensitized TiO2 photoanodes were fabricated for quantum dots sensitized solar cells (QDSSC) and their photovoltaic response were studied. Pure CdTe QDs and Yb doped CdTe QDs were prepared in aqueous phase by using mercaptosuccinic acid as a capping agent. The influence of dopant material on structural properties of CdTe QDs were studied by XRD analysis, which confirms that prepared QDs belongs to cubic zinc blende crystalline structure and the size of CdTe QDs were decreased with increasing dopant concentration. The dopant concentration dependent optical properties were studied by UV–vis absorption and fluorescence emission studies. Elemental composition of pure and Yb doped CdTe QDs were examined by EDX analysis and their formation were studied by XPS analysis. Capping of MSA molecules over CdTe QDs was confirmed by FT-IR analysis. Photovoltaic performance of pure and Yb doped CdTe QDs sensitized TiO2 photoanodes was studied by fabrication of QDSSC using polysulfide electrolyte. J–V characteristic curves reveal the enhanced solar cell efficiency of Yb doped CdTe QDs sensitized photoanodes.