Bulk CdTe Research Articles

Hyper‐Elastic Deformation via Martensitic Phase Transformation in Cadmium Telluride

Cadmium telluride (CdTe) is a highly promising material for photovoltaics (PV) and photodetectors due to its light‐absorbing properties. However, efficient design and use of flexible devices require a deep understanding of its atomic‐level deformation mechanism. Herein, uniaxial compression deformation of CdTe monocrystalline with varying crystal orientations is investigated using molecular dynamics (MD) with a newly developed machine‐learning force field (ML‐FF), alongside in‐situ micropillar compression experiments. The findings reveal that CdTe bulk deformation is dominated by reversible martensitic phase transformation, whereas CdTe pillar deformation is primarily driven by dislocation nucleation and movement. CdTe monocrystals possess exceptional super‐recoverable deformation along the <100> orientation due to hyper‐elastic processes induced by martensitic transformation. This discovery not only sheds light on the peculiarities observed in micropillar experimental measurements, but also provides pivotal insights into the fundamental deformation behaviors of CdTe and similar II–VI compounds under various stress conditions. These insights are crucial for the innovative design and enhanced functionality of future flexible electronic devices.

High-harmonic generation in CdTe with ultra-low pump intensity and high photon flux

An ultra-low pump intensity and high photon flux have been long pursuits of high harmonic generation (HHG) in solids. However, there is lack of a criterion to identify a pristine solid material exhibiting such characteristics. Here, we report systematic investigation into HHG from a cadmium telluride (CdTe) bulk crystal with a flat band dispersion near the Fermi level which leads to a large density of states. The measured pump intensity for the 31st harmonics (229 nm) is only 75 GW/cm2, one order of magnitude lower than that of other pristine crystals including two-dimensional materials reported so far. A comparative measurement shows CdTe has two-to-three orders of magnitude stronger HHG than silicon does, and high HHG yields in the ultraviolet region compared to GaSe. A high photon flux of ~ 6 × 1012 photons/s (5th−8th) with a robust long-time sustainability is obtained. This work offers a route towards compact vacuum ultraviolet laser sources.

Quantum-dimensional near-surface recombination of photocarriers in CdTe microcrystals

The low-temperature (T = 2 K) photoluminescence spectra of a p-CdTe/n-CdS film heterostructure containing CdTe microcrystals have been studied. In the spectral region above the intrinsic absorption edge of bulk CdTe, a dominant “superhot” radiation band was found. The band arises because of optical transitions of electrons from near-surface levels of the spatial quantization of a microcrystal to the valence band states.

Electrodeposition of CdTe thin films using an acetate precursor for solar energy application: The effect of deposition voltage

Cadmium Telluride (CdTe) thin films were synthesized using a low-cost two-electrode electrodeposition configuration in potentiostatic mode and from an aqueous acidic solution. More commonly used cadmium salts for electrodeposition of CdTe include CdSO4, CdCl2 and Cd (NO3)2. In the present work, a less commonly used salt, cadmium acetate, was used as a cadmium precursor for the growth of CdTe thin films. The thin films were deposited on a coated glass fluorine- doped tin oxide (FTO) substrates. The deposition voltage was varied from 1230 to 1270 mV with a 10 mV increment. The structure, optical, conductivity, surface morphological, elemental composition, and surface roughness properties of the as-deposited thin films were investigated by using X-ray diffraction (XRD), UV–VIS spectrophotometry, Photoelectrochemical cell analysis (PEC), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and scanning probe microscopy (SPM), respectively. The XRD results showed that the CdTe thin films displayed a higher intensity at 1250 mV deposition voltage. UV–VIS spectroscopy measurements revealed that the band gap of the CdTe thin films was near that of the bulk CdTe at 1250 mV deposition voltage. The PEC measurement indicated that at a low voltage of 1230 mV, the conductivity of the film was p-type and Te-rich. When the deposition voltage was 1270 mV, the CdTe films became n-type and Cd-rich. EDS results confirmed the presence of both Cd and Te with more stoichiometric values at the growth voltage of 1250 mV. The SEM images showed that the surface morphology changed with deposition voltage. SPM results indicated that the highest average surface roughness value of 94.9 nm was obtained with a deposition voltage of 1250 mV. These results indicate that the film prepared at a deposition voltage of 1250 mV, may have better potential application as an absorber layer in solar cell device.

Surface Quantum-Dimensional Photocarrier Recombination in <i>CdTe</i> Microcrystals

The scope of the study is the spectra of low-temperature (T = 2K) photoluminescence of a p-CdTe/n-CdS film heterostructure comprising a monolayer of CdTe microcrystals, where a single microcrystalline particle is typically one micron in size. Focus is made on the dominant band of “super-hot” emission appearing in the spectral region located in energy above the fundamental absorption edge of a CdTe bulk crystal. A theoretical model has been developed that assumes the existence of a space-charge layer inside a microcrystal, which leads to the formation of a triangular potential well for an electron near the surface. The anomalous emission band arises as a result of the optical transitions of electrons from near-surface levels of spatial quantization to valence band states.

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.

Low-Temperature Annealing of CdTe Detectors With Evaporated Gold Contacts and Its Effect on Detector Performance

Cadmium telluride (CdTe) detectors are usually subjected to elevated temperatures during postprocessing and bonding them to readout electronics while fabricating imaging arrays. We studied the effects of low-temperature and short duration rapid thermal annealing of CdTe bulk as well as CdTe epitaxial-layer-based detectors with evaporated gold contacts. The detectors were annealed in the temperature range of 100 °C–300 °C, and its effect on the detector dark current, gamma detection property, and response stability was studied. For the bulk-detectors, the detector dark current decreased and gamma detection properties as well as the performance stability improved after annealing. However, such improvements were moderate for epitaxial-layer-based detectors. The study of the metal–semiconductor interface of annealed detectors revealed that diffused gold, elemental oxygen, and tellurium oxide existed and extended deep inside the bulk portion in epitaxial detectors; however, they were confined in the surface regions only in bulk-detectors, which likely be the causes of observed results in these two types of detectors.

Recombination-induced voltage-dependent photocurrent collection loss in CdTe thin film solar cell

Recently, the efficiency of CdTe thin film solar cell has been improved by using new type of window layer Mg x Zn1−x O (MZO). However, it is hard to achieve such a high efficiency as expected. In this report a comparative study is carried out between the MZO/CdTe and CdS/CdTe solar cells to investigate the factors affecting the device performance of MZO/CdTe solar cells. The efficiency loss quantified by voltage-dependent photocurrent collection efficiency (η C(V′)) is 3.89% for MZO/CdTe and 1.53% for CdS/CdTe solar cells. The higher efficiency loss for the MZO/CdTe solar cell is induced by more severe carrier recombination at the MZO/CdTe p–n junction interface and in CdTe bulk region than that for the CdS/CdTe solar cell. Activation energy (E a) of the reverse saturation current of the MZO/CdTe and CdS/CdTe solar cells are found to be 1.08 eV and 1.36 eV, respectively. These values indicate that for the CdS/CdTe solar cell the carrier recombination is dominated by bulk Shockley–Read–Hall (SRH) recombination and for the MZO/CdTe solar cell the carrier recombination is dominated by the p–n junction interface recombination. It is found that the tunneling-enhanced interface recombination is also involved in carrier recombination in the MZO/CdTe solar cell. This work demonstrates the poor device performance of the MZO/CdTe solar cell is induced by more severe interface and bulk recombination than that of the CdS/CdTe solar cell.

Strategy trends of core/multiple shell for quantum dot-based heterojunction thin film solar cells

ABSTRACT Design structure of semiconductor window and absorber layers’ materials in thin film solar cells is an essential trend for specifying optical and electrical characteristics of thin film solar cells. This paper has been improved the optical and electrical characteristics and efficiency of traditional HJ-QDSc (ITO/CdS/QDPbS/Au) model by using the quantum dot window layer instead of bulk structure layers’ cell. Moreover, this paper represents new design for absorber layer using QD aluminium core/PbS shell absorber layer structure instead of QD PbS absorber layer to use the merits of QD metallic-semiconductor core/multiple shell structure to enhance the performance of previous CdS/QDPbS HJ-QDSc model. The proposal design structure is carried out by replacing the bulk CdTe, CIGS absorber layers and CdS window layer with quantum dot size window layer material and QD core/multiple shell absorber layer based on traditional (SnO2/CdS/CdTe/Cu) and (ZnO/CdS/CIGS/Mo). The proposal design structure on three-types of core/multiple shell for quantum dot based on heterojunction thin film solar cells has been applied. A comparison study has been established between the proposal design and traditional thin film solar cells based on sub-micro absorber layer thickness models.

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.

High resolution synchrotron extended x-ray absorption fine structure and infrared spectroscopy analysis of MBE grown CdTe/InSb epifilms

Six CdTe thin epifilms were prepared by using molecular beam epitaxy on ion beam cleaned InSb (001) substrates with Tsub temperatures ranging from 25 to 250 °C. Thickness dependent vibrational and structural characteristics are meticulously examined by far-infrared reflectivity (FIR) and high-resolution synchrotron extended x-ray absorption spectroscopy (HR-XAS), respectively. The FIR measured line shapes and optical modes for samples prepared on ion beam cleaned InSb at Tsub ≤ 100 °C revealed abrupt interfaces while noticing segregated Sb atoms and In2Te3-like precipitates at CdTe-InSb interfaces for films grown on ion beam cleaned InSb at Tsub ≥ 230 °C. Our simulated reflectivity results, using a traditional multilayer (ambient/film/substrate) optics methodology, are compared reasonably well with the experimental data. To substantiate the Berreman effect, we have also investigated the transmission and reflectivity spectra of CdTe/InSb epilayers and (CdTe)m/(ZnTe)n/InSb superlattices at oblique incidence (θI = 45°). A clear distinction of the transverse optical (ωTO) phonons in the s-polarization and ωTO and longitudinal optical (ωLO) modes in the p-polarization has established a valuable method of assessing long wavelength optical phonon frequencies in technologically important materials. Comprehensive analysis of HR-XAS results on the structural characteristics of CdTe/InSb epilayers has provided values of bond lengths and coordination numbers in very good agreement with the existing bulk CdTe data.

Charge-carrier thermalization in bulk and monolayer CdTe from first principles

While cadmium telluride (CdTe) thin films are being used in solar cell prototyping for decades, the recent advent of two-dimensional (2D) materials challenges the fundamental limit for thickness of conventional CdTe layers. Here, we report our theoretical predictions on photocarrier dynamics in an ultimately thin (about 1 nm) CdTe slab. It corresponds to a layer that is just a single unit cell thick, when the bulk parent crystal in the zinc blende phase is cleaved along the [110] facet. Using an \textit{ab-initio} method based on density functional theory (DFT) and the Boltzmann equation in the relaxation time approximation (RTA), we determine the thermalization time for charge carriers excited to a certain energy for instance through laser irradiation. Our calculations include contributions arising from all phonon branches in the first Brillouin zone (BZ), thus capturing all relevant inter- and intraband carrier transitions due to electron-phonon scattering. We find that the photocarrier thermalization time is strongly reduced, by one order of magnitude for holes and by three orders of magnitude for electrons, once the CdTe crystal is thinned down from the bulk to a monolayer. Most surprisingly, the electron thermalization time becomes independent of the electron excess energy up to about 0.5~eV, when counted from the conduction band minimum (CBM). We relate this peculiar behavior to the degenerate and nearly parabolic lowest conduction band that yields a constant density of states (DOS) in the 2D limit. Our findings may be useful for designing novel CdTe-based optoelectronic devices, which employ nonequilibrium photoexcited carriers to improve the performance.

Chlorine passivation of grain boundaries in cadmium telluride solar cells

Cadmium telluride is the most commercially important second generation thin-film photovoltaic, with a record solar cell conversion efficiency of 22.1%. However as-deposited cells are 5% efficient and require a cell activation treatment with ${\mathrm{CdCl}}_{2}$ at about 400 ${}^{\ensuremath{\circ}}\mathrm{C}$ to reach commercially viable efficiencies. Such a treatment is a routine process during CdTe module manufacturing. However, the precise mechanisms at work for this remarkable efficiency enhancement are not well understood. In this paper, atomistic modeling techniques are used to improve the fundamental understanding of the structural and electronic properties of CdTe by modeling the effects of chlorine and other elements with their interaction with extended defects and grain boundaries (GBs). Studies at high spatial resolution with nanoscale secondary ion mass spectrometry, transmission electron microscopy (TEM), and energy dispersive x-ray analysis show that chlorine atoms are concentrated at grain boundaries in CdTe after the ${\mathrm{CdCl}}_{2}$ treatment. Density functional theory calculations show that both ${\mathrm{Cl}}_{\mathrm{Te}}$ and ${\mathrm{Cl}}_{i}$ are stabilized at the grain boundaries compared to bulk CdTe. Similar defect formation energies of these defects suggest both will be present at the grain boundaries. As expected, four single-particle levels are present in the $\mathrm{\ensuremath{\Sigma}}3$ (112) GB band gap, which explains the low efficiencies prior to treatment. ${\mathrm{Cl}}_{\mathrm{Te}}$ substitutions passivate one of these levels and partially passivate another two. Remarkably, further addition of ${\mathrm{Cl}}_{i}$ fully passivates the remaining single-particle levels. This passivation of single-particle levels is most likely to be the primary cause of the efficiency enhancement on chlorine treatment. Further to this, alternative halogens were then trialed as activation treatments. All halogens show similar electronic effects and their defect formation energies follow ionic radii trends.

Linear and nonlinear optical response dependency on the crystallite size of CdTe and its structural properties

Cadmium telluride QD thin films of thickness (10→57 nm) has been successfully synthesized using inert gas condensation. The structure of thin films was examined by grazing incident in-plane X-ray diffraction (GIIXD), revealing a hexagonal polymorph structure. A strong confinement regime was achieved where the attained radius (from ~2.6 to 6 nm) of particle size of thin films was smaller than the Bohr radius of their bulk CdTe (~7.3 nm). Linear and nonlinear optical properties were affected by changing the particle size. The optical gap is higher than that of bulk CdTe, it increased from 2.44 to 2.8 eV as film thickness decreased from 57 to 10 nm. All optical parameters such as dispersion parameters (Eso and Ed), oscillator strength (f), lattice dielectric constant (εL), static dielectric constant (εo) and refractive index (no) were increased with film thickness. Likewise, the linear and nonlinear susceptibility (X(1), X(3)) besides nonlinear refractive index (n2) increased with film thickness.

Structural and Electronic Calculations of CdTe Using DFT: Exchange–Correlation Functionals and DFT-1/2 Corrections

Ab initio calculations were performed to investigate the structural and electronic properties of bulk CdTe using various exchange–correlation (XC) functionals available. Among the selected XC functionals include the local density approximation (LDA), generalized gradient approximation (GGA), meta-generalized gradient approximation (MGGA) (using the linear combination of atomic orbitals basis scheme) and Heyd–Scuseria–Ernzerhof-06 (HSE06) (using the plane-wave basis scheme). Further computational studies were performed based on the local density approximation-1/2 (LDA-1/2) and generalized gradient approximation-1/2 (GGA-1/2) self-energy correction schemes to verify their effect on the CdTe band gap in comparison to the other traditional XC functionals. The lattice parameter values obtained using different XC functionals (LDA, GGA and MGGA) were well in agreement with experimental value, with LDA predicting 6.548 A. This is 1.02% greater than the experimental value of 6.482 A. The electronic structure of CdTe was calculated for the fixed 6.482 A lattice parameter of bulk CdTe and resulted in a band gap ranging between 0.68 and 1.56 eV for LDA, GGA, MGGA, and HSE06. The band gap values predicted by the LDA-1/2 and GGA-1/2 corrections were 1.47 eV and 1.50 eV, respectively, and are found to be in good agreement with experimental values. The influence of XC functionals and semi-empirical correction schemes are expected to have important implications on the prediction and understanding of bulk CdTe thin-films found in photovoltaic applications.

Temperature- and size-dependent photoluminescence in colloidal CdTe and Cd x Zn1−x Te quantum dots

Semiconductor colloidal quantum dots (QDs) of CdTe and alloyed Cd x Zn1−x Te QDs with N-acetyl-L-cysteine capping ligands are synthesized by a reflux method in aqueous solution. Alloying provides a new degree of freedom to tune the optical and electronic properties of the nanocrystals. The photoluminescence (PL) of Cd x Zn1−x Te QDs is sharper and displays a highly enhanced quantum yield (QY) of 65% relative to the 16% of CdTe QDs. The fluorescence of Cd x Zn1−x Te QDs is observed to be highly stable for over 12 months without degradation, while that of CdTe QDs begins to mildly flocculate around 8 months of storage. To characterise the material structure and composition, UV-Vis absorption spectroscopy, x-ray powder diffraction, transmission electron microscopy, and inductively coupled plasma mass spectrometry measurements are carried out. To understand the fundamental processes that play in the luminescence behaviour, temperature- and size-dependent PL spectra are investigated in the range 80–300 K. The Varshni and O’Donnell equations fit well on the PL peak emission energies and the Huang–Rhys parameter indicates the strengthening of exciton–phonon coupling in the nanocrystals upon alloying and with decreasing nanocrystal sizes. PL linewidth analysis reveals that the inhomogeneous broadening is considerably reduced in Cd x Zn1−x Te QDs relative to CdTe. Moreover, the quantum confinement effect of the nanocrystals leads to an increase in exciton–acoustic phonon interactions with the coefficients ranging between 26.9 and 95.6 µeV K−1 compared to the bulk CdTe value of 0.72 µeV K−1. Exciton–longitudinal optical phonon interactions are made stronger by the ZnTe alloying with the coefficients lying in the range between 24.8 and 41.7 meV and also with the effect of increasing crystal size. An Arrhenius plot of PL integrated area is used to calculate the thermal activation energy value E a of the non-radiative recombination channel, which is 132 meV for CdTe QDs and a higher value of 185 meV for Cd x Zn1−x Te QDs. This is consistent with the observed QY enhancement in Cd x Zn1−x Te QDs as a higher E a value indicates reduced generation of non-radiative recombination centres and a decrease in defect densities upon alloying. Cd x Zn1−x Te QDs with enhanced fluorescence properties serve both as a medium for studying fundamental effects of alloying and its properties, and for practical applications such as biomedical labelling and optoelectronics.

Influence of phosphorus ion implantation on the optical properties of CdTe bulk crystal

Bulk CdTe crystals were implanted with 400 keV phosphorus ions to investigate the dopability of the host material. Induced devastation in crystal structure related to changes in optical constants of the material was examined by UV–Vis-IR transmittance measurements and spectrometric ellipsometry in a wide range of energies, corresponding to 200–2500 nm for transmittance and 191–2000 nm for ellipsometry. We used phosphorus particle fluences in a range of 5⋅1013 to 5⋅1016 P/cm2. Such fluences should provide p-type dopants concentration at a range of 1018 to 1021 P/cm3 assuming an average range of implanted ions (R) and longitudinal straggling (SR) as R ± SR = 403 ± 166 nm as estimated by SRIM software. The highest doping level was achieved with minor damages in the host lattice. Charged phosphorus particles implanted into bulk CdTe produce sublayer of CdTe:P, indicated by changes in the optical constants and luminescence. It was also observed that the doped layer of CdTe:P affects the transmittance of the crystals. Room temperature micro-Raman spectra of implanted samples, obtained with 532 nm and 785 nm lasers, do not differ from those for an undoped CdTe crystal. Luminescence measurements performed at temperature range down to 11 K show great improvement in luminescence emission, strong band-acceptor excitonic emission (A,X), exciton binding energy EXB = 8.7 meV and shallow acceptor level established by P-ion at about 19.1 meV above valence band maximum (VBM). We concluded that bulk crystals can be successfully doped with phosphorus ion of 400 keV energy up to ion fluences at the range of 5∙1016 P/cm2.

Consequences of surface coatings and soil ageing on the toxicity of cadmium telluride quantum dots to the earthworm Eisenia fetida.

The bioaccumulation potential and toxic effects of engineered nanomaterials (ENMs) to earthworms are poorly understood. Two studies were conducted following OECD TG 222 on Eisenia fetida to assess the effects of CdTe QDs with different coatings and soil ageing respectively. Earthworms were exposed to carboxylate (COOH), ammonium (NH4+), or polyethylene glycol (PEG) coated CdTe QDs, or a micron scale (bulk) CdTe material, at nominal concentrations of 50, 500 and 2000 mg CdTe QD kg-1 dry weight (dw) for 28 days in Lufa 2.2 soil. In the fresh soil study, earthworms accumulated similar amounts of Cd and Te in the CdTe-bulk exposures, while the accumulation of Cd was higher than Te during the exposures to CdTe QDs. However, neither the total Cd, nor Te concentrations in the earthworms, were easily explained by the extractable metal fractions in the soil or particle dissolution. There were no effects on survival, but some retardation of growth was observed at the higher doses. Inhibition of Na+/K+-ATPase activity with disturbances to tissue electrolytes, as well as tissue Cu and Mn were observed, but without depletion of total glutathione in the fresh soil experiment. Additionally, juvenile production was the most sensitive endpoint, with estimated nominal EC50 of values >2000, 108, 65, 96 mg CdTe kg-1 for bulk, PEG-, COOH- and NH4+-coated CdTe QDs, respectively. In the aged soil study, the accumulation of Cd and Te was higher than in the fresh soil study in all CdTe QD exposures. Survival of the adult worms was reduced in the top CdTe-COOH and -NH4+ QD exposures by 55 ± 5 and 60 ± 25%, respectively; and with decreases in growth. The nominal EC50 values for juvenile production in the aged soil were 165, 88, 78 and 63 mg CdTe kg-1 for bulk, PEG-, COOH- and NH4+-coated CdTe QDs, respectively. In conclusion, exposure to nanoscale CdTe QDs, regardless of coating, caused more severe toxic effects that the CdTe bulk material and the toxicity increased after soil ageing. There were some coating-mediated effects, likely due to differences in the metal content and behaviour of the materials.

Design modern structure for heterojunction quantum dot solar cells

This paper proposal new structure for improving the optical, electrical characteristics and efficiency of 3rd generation heterojunction quantum dot solar cell (HJQDSC) (ITO/CdS/QDPbS/Au) model by using the quantum dot window layer instead of bulk structure layers cell. Also, this paper presents theoretically analysis for the performance of the proposal HJQDSC (ITO/QDCdS/QDPbS/Au) structure. The new design structure was applied on traditional (SnO2/CdS/CdTe/Cu) and (ZnO/CdS/CIGS/Mo) thin film solar cells which based on sub-micro absorber layer thickness models by replacing the bulk CdTe, CIGS absorber layers and CdS window layer with quantum dot size materials to achieve higher efficiency with lesser usage layer material. Also, it has been studied the effect of using semiconductors layers in quantum dots size on electric and optical properties of thin film solar cells and the effect of window and absorber layers quantum dots radii on the performance of solar cells. Finally, a thermal efficiency analysis has been investigated for explaining the importance of new structure HJQD solar cells.

Maximize CdTe solar cell performance through copper activation engineering

Abstract The incorporation of copper (Cu) is one of the critical processes for fabricating high-efficiency CdTe thin-film solar cells. However, due to its high mobility in CdTe, the distribution and concentration of Cu must be carefully engineered to reduce the compensative donor-like interstitial defects in CdTe bulk and the recombination centers at the buffer layer/CdTe interface to maximize device performances. Here, a cuprous chloride (CuCl) solution treatment and a rapid thermal annealing (RTA) process are used to control the concentration and distribution of Cu in CdTe absorbers, enabling a champion CdTe thin-film solar cell with a power conversion efficiency of 17.5% without selenium incorporation. The results demonstrate that the use of a CuCl solution can substantially reduce the amount of Cu needed in CdTe and the RTA process is a viable approach to engineer the Cu distribution in CdTe solar cells.