Pronounced Impact of p-Type Carriers and Reduction of Bandgap in Semiconducting ZnTe Thin Films by Cu Doping for Intermediate Buffer Layer in Heterojunction Solar Cells

DC current-voltage and impedance spectroscopy characterization of nCdS/pZnTe HJ

This paper describes the electrical and dielectric behavior of the nCdS/pZnTe HJ by current-voltage, capacitance-voltage characteristics, and impedance spectroscopy in a temperature interval 220-350 K. A microcrystalline p-ZnTe layer and n-CdS were grown on glass/ZnO substrate by closed space sublimation method. As frontal contact to CdS, the transparent ZnO and as a back contact to ZnTe, silver conductive paste (Ag) treated at 50 °C in vacuum were used. The current-voltage results of nCdS/pZnTe HJ show a rectifying behavior. The junction ideality factor, barrier height, and series resistance values were extracted from the rectifying curves at different temperatures. The built-in voltage, carrier concentration and depletion width were obtained from the capacitance-voltage measurements. Analysis of the J-V-T and C-V-T characteristics shows that the thermionic emission and recombination current flow mechanisms dominate in the nCdS/pZnTe HJ. The dielectric study reveals that the experimental values of the AC conductivity, dielectric constant, dielectric loss, the imaginary part of the electric modulus are found to be very sensitive to frequency and temperature. The dielectric constant and dielectric loss are observed to be high at the low frequency region. The increase in the values of electric modulus with the frequency implies an increase in the interfacial polarization at the interface of nCdS/pZnTe HJ. Jonscher's universal power law shows that with increasing frequency, AC conductivity increased. The results conductivity show that the ionic conductivity and interfacial polarization are the main parameters affecting the dielectric properties of the device when the temperature changes.

A comprehensive review of flexible cadmium telluride solar cells with back surface field layer

Recent advancements in CdTe solar cell technology have introduced the integration of flexible substrates, providing lightweight and adaptable energy solutions for various applications. Some of the notable applications of flexible solar photovoltaic technology include building integrated photovoltaic systems (BIPV), transportation, aerospace, satellites, etc. However, despite this advancement, certain issues regarding metal and p-CdTe remained unresolved. Besides, the fabrication of a full-working device on flexible glass is challenging and requires special consideration due to the unstable morphology and structural properties of deposited film on ultra-thin glass substrates. The existing gap in knowledge about the vast potential of flexible CdTe solar cells on UTG substrates and their possible applications blocks their full capacity utilization. Hence, this comprehensive review paper exclusively concentrates on the obstacles associated with the implementation of CdTe solar cells on UTG substrates with a potential back surface field (BSF) layer. The significance of this study lies in its meticulous identification and analysis of the substantial challenges associated with integrating flexible CdTe onto UTG substrates and leveraging Cu-doped ZnTe as a potential BSF layer to enhance the performance of flexible CdTe solar cells.

Resulting Effect of the p-Type of ZnTe: Cu Thin Films of the Intermediate Layer in Heterojunction Solar Cells: Structural, Optical, and Electrical Characteristics

The microstructural, electrical, and optical properties of Cu-doped and undoped ZnTe thin films grown on glass substrates are covered in this article. To determine the chemical makeup of these materials, both energy-dispersive X-ray (EDAX) spectroscopy and X-ray photoelectron spectroscopy were employed. The cubic zinc-blende crystal structure of ZnTe and Cu-doped ZnTe films was discovered using X-ray diffraction crystallography. According to these microstructural studies, the average crystallite size increased as the amount of Cu doping increased, whereas the microstrain decreased as the crystallinity increased; hence, defects were minimized. The Swanepoel method was used to compute the refractive index, and it was found that the refractive index rises as the Cu doping levels rises. The optical band gap energy was observed to decrease from 2.225 eV to 1.941 eV as the Cu content rose from 0% to 8%, and then slightly increase to 1.965 eV at a Cu concentration of 10%. The Burstein-Moss effect may be connected to this observation. The larger grain size, which lessens the dispersion of the grain boundary, was thought to be the cause of the observed increase in the dc electrical conductivity with an increase in Cu doping. In structured undoped and Cu-doped ZnTe films, there were two carrier transport conduction mechanisms that could be seen. According to the Hall Effect measurements, all the grown films exhibited a p-type conduction behavior. In addition, the findings demonstrated that as the Cu doping level rises, the carrier concentration and the Hall mobility similarly rise, reaching an ideal Cu concentration of 8 at.%, which is due to the fact that the grain size decreases grain boundary scattering. Furthermore, we examined the impact of the ZnTe and ZnTe:Cu (at Cu 8 at.%) layers on the efficiency of the CdS/CdTe solar cells.

The synthesis of CdZnTe semiconductor thin films for tandem solar cells

A new approach is adopted to grow cadmium zinc telluride (CdZnTe) thin films using the close spaced sublimation (CSS) technique. The deposition parameters for the growth of cadmium telluride (CdTe) thin films onto the glass substrate were optimized. A zinc telluride (ZnTe) thin film layer was deposited onto already-deposited CdTe thin film to fabricate the CdZnTe (CZT) thin film sample as a ternary compound. Annealing was done after the successful deposition of CZT thin films before further characterization of the CZT thin film samples. The structures of the CZT thin film samples were studied using X-ray diffraction (XRD) and cubic phases were found. A spectrophotometer was used to study the optical parameters, and the energy band gap was found to be in the range of 1.45 eV to 1.75 eV after annealing. The nature of the direct band gap predicts that it might be an ideal component in second-generation solar cells. A Hall measurement system was used to find that the electrical conductivity was in the range of 4.6 × 10-6 to 8.2 × 10-11 (ohm cm)-1. XPS analysis confirmed the presence of Zn in the CdTe thin films. A significant change in electronic properties was observed. These results show that these CZT thin film samples can not only play a key role in the tandem structures of high-efficiency solar cells but they could also be used in the detection of X-rays and gamma rays.

Cation exchange mediated synthesis of bright Au@ZnTe core-shell nanocrystals

The synthesis of heterostructured core-shell nanocrystals has attracted significant attention due to their wide range of applications in energy, medicine and environment. To further extend the possible nanostructures, non-epitaxial growth is introduced to form heterostructures with large lattice mismatches, which cannot be achieved by classical epitaxial growth techniques. Here, we report the synthetic procedure of Au@ZnTe core-shell nanostructures by cation exchange reaction for the first time. For that, bimetallic Au@Ag heterostructures were synthesized by using PDDA as stabilizer and shape-controller. Then, by addition of Te and Zn precursors in a step-wise reaction, the zinc and silver cation exchange was performed and Au@ZnTe nanocrystals were obtained. Structural and optical characterization confirmed the formation of the Au@ZnTe nanocrystals. The optimization of the synthesis led to the bright nanocrystals with a photoluminescence quantum yield up to 27%. The non-toxic, versatile synthetic route, and bright emission of the synthesized Au@ZnTe nanocrystals offer significant potential for future bio-imaging and optoelectronic applications.