Factors Affecting Electroplated Semiconductor Material Properties: The Case Study of Deposition Temperature on Cadmium Telluride

Abstract

Electrodeposition of cadmium telluride (CdTe) on fluorine doped tin oxide (FTO) using two electrode configurations was successfully achieved with the main focus on the growth temperature. The electroplating temperatures explored ranged between 55 and 85 • C for aqueous electrolytes containing 1.5 M cadmium nitrate tetrahydrate (Cd(NO 3 ) 2 ·4H 2 O) and 0.002 M tellurium oxide (TeO 2 ). The ensuing CdTe thin-films were characterized using X-ray diffraction (XRD), UV-Vis spectrophotometry, scanning electron microscopy (SEM), energy dispersive X-ray (EDX), and photoelectrochemical (PEC) cell measurements. The electroplated CdTe thin-films exhibit a dominant (111) CdTe cubic structure, while the crystallite size increases with the increase in the electroplating temperature. The dislocation density and the number of crystallites per unit area decrease with increasing growth temperature. The optical characterization depicts that the CdTe samples show comparable absorbance and a resulting bandgap of 1.51 ± 0.03 eV for as-deposited CdTe layers. A marginal increase in the bandgap and reduction in the absorption edge slope towards lower deposition temperatures were also revealed. The annealed CdTe thin-films showed improvement in the energy bandgap as it tends towards 1.45 eV while retaining the aforementioned absorption edge slope trend. Scanning electron microscopy shows that the underlying FTO layers are well covered with increasing grain size observable relative to the increase in the deposition temperature. The energy dispersive X-ray analyses show an alteration in the Te/Cd relative to the deposition temperature. Higher Te ratio with respect to Cd was revealed at deposition temperature lower than 85 • C. The photoelectrochemical cell study shows that both pand n-type CdTe can be electroplated and that deposition temperatures below 85 • C at 1400 mV results in p-type CdTe layers.Coatings 2019, 9, 370 2 of 15 cadmium telluride (CdTe) thin-films can be grown and incorporated for different applications. CdTe is one of the II-VI semiconductor materials that has been grown using several techniques including electroplating [4,5] and has been extensively researched owing to its properties [6]. Due to the direct bandgap of CdTe at room temperature (~1.45 eV), it is capable of absorbing a substantial fraction of the electromagnetic spectrum under AM1.5 conditions. This characteristic has been explored in the photovoltaic (PV) community in achieving high-efficiency CdTe-based solar cells [7]. The recent hike in the conversion efficiency from 16.5% in 2004 [8] to 22.1% in 2016 [9] as reported in the literature is mainly due to the eradication of defects within the crystal lattice or traps within the bandgap in addition to improved crystallinity, passivation of the grain boundaries which is due to better understanding of both material and device issues. Therefore, it is fundamental to strive towards process optimization amongst others. Under both two and three-electrode electrodeposition configurations, different deposition temp...

Special Issue: “Advanced Thin Film Materials for Photovoltaic Applications”

“…This Special Issue consists of ten fully refereed scientific publications: seven open access articles [4][5][6][7][8][9][10] and three open access review articles [11][12][13]. The seven articles provide information on perovskite, SnS/SnS 2 , CdTe, CIGS, silicon and transparent conducting oxide (SnO 2 ) materials used in solar cell development.…”

“…The seven articles provide information on perovskite, SnS/SnS 2 , CdTe, CIGS, silicon and transparent conducting oxide (SnO 2 ) materials used in solar cell development. One of these articles is a featured paper on electrodeposition of CdTe [7]. Out of the three review articles, one summarises the CdTe (1−x) Se x thin films in solar cell applications [11].…”

“…The work focuses on the PL transitions close to the bandgap of CdTe. Ojo and Dharmadasa [7] present the results of electroplated CdTe material grown for use in CdS/CdTe solar cells. This article focuses on a case study of the temperature-dependent properties of electroplated CdTe thin films.…”