Investigation of Cd1-xZnxTe and CdMgS Thin Films for Energy Conversion Material Using Experimental and Theoretical Approaches

Abstract

Cadmium telluride (CdTe), Cadmium zinc telluride (CdZnTe), and Cadmium magnesium sulfide (CdMgS) thin films were generated in an acidic aqueous solution utilizing a low-cost two-electrode (TE) electrodeposition (ED) technique. The CdTe thin films were synthesized at various cathodic voltages to investigate the deposition voltage range from (1200 -1450) mV with a 50 mV raise. The structural, optical, and Photoelectrochemical cell study shows that the film deposited at 1250 mV will be taken as optimized voltage. CdTe thin films were synthesized at different deposition pHs, such as 1.8, 2.5, 3.0, and 3.5. According to the structural study, the deposited CdTe thin films feature mixed-phase hexagonal and cubic zinc blend structures in their as-prepared (AD) and annealed (HT) forms, with pH depositions of 1.8, 2.5, and 3.5. When the pH of the depositing reaches 3.0, only a single-phase cubic structure is visible. The maximum crystallite size is 23 nm HT samples for conforming pH values 3.0. For AD samples, the energy bandgaps were measured (1.38 - 1.58) eV, and for HT (1.35 - 1.5) eV, for a range between (1.8 - 3.5) pH values. The entire outcome demonstrates that a CdTe film of high quality for solar cell (SC) usage was formed at a pH of 3.0. The structural study reveals that CdZnTe thin films are cubic structures. The band gap of CdZnTe was increased from (1.82-2.12) eV for AD samples and (1.52-1.74) eV for HT samples with (0.25-1.00) M Zn concentrations, respectively. The structural analysis of CdS: Mg verified the formation of hexagonal films. The CdS: Mg thin films had the least surface morphology at a deposition voltage of 1450 mV. When the cathodic voltage was used between (1445 -1465) mV, the energy band gap of CdS: Mg thin films was in the range (2.44 - 2.47) eV. Results from Raman spectroscopy exhibited that the first longitudinal optic (1LO) phonon vibration revealed a high peak at 306 cm−1 wave number. With the possibility of being used as a buffer layer in thin-film CdTe-based SC systems, the film deposited at 1450 mV demonstrated the best quality. CdZnTe structural optimization, state density, and electron energy band structure are studied using DFT. The optical spectra of CdTe and CdZnTe are calculated, including the real and imaginary parts of dielectric parameters, energy loss functions, absorption coefficient, reflective index, and conductivity, and the analysis confirmed that the values varied with Zn- concentration.