Abstract
Two-electrode (2E) configuration was successfully utilised in the electrochemical deposition of cadmium telluride (CdTe) on fluorine-doped tin oxide (FTO) substrate with the main emphasis on the electrolytic bath pH. The electrochemical deposition pH explored is within the range of (1.00 to 6.00)±0.02 for the aqueous electrolyte comprising of tellurium oxide (TeO2) and cadmium nitrate (Cd(NO3)2) which are the respective precursors of Te and Cd. The optical, structural, morphological, compositional, and electrical properties of the electroplated CdTe thin-films were respectively explored using UV-Vis spectrophotometry, X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), and photoelectrochemical (PEC) cell measurements. The optical characterisation show that the CdTe samples exhibit dissimilar absorbance depending on the growth pH for both the as-deposited layers and post-growth treated CdTe layers. A decrease in the absorption edge slope and dip in the bandgap was observed away from pH2. The bandgap of the post-growth treated CdTe layers showed enhancement as it leans towards 1.45 eV, with the trend retention of absorption edge slope, similar to the as-deposited CdTe layers. The electrodeposited CdTe thin-films show a dominant orientation along the cubic (111) CdTe plane, while both the the calculated crystallite size and the XRD peak intensity Pi decreases with the electroplating pH outside the (2.00 to 3.00)±0.02 range. The EDX analyses depicts an alteration in the ratio of Cd to Te atomic percentage relative to the pH of the electrolyte. Comparatively high Te atomic ratio was observed at lower pH values and vice versa with increase alkalinity of the electrolyte. The obtained morphology depicts that the underlying FTO layers are well covered with a gradual reduction in the grain size of the CdTe observable away from pH value (2.00 and 3.00). The photoelectrochemical cell study depicts that the conduction type of the CdTe layers can also be attributed to the CdTe-electrolytic bath pH value.
Highlights
II-VI semiconductor material such as Cadmium telluride (CdTe) is well-recognised in the photovoltaic (PV) community due to its optimal and direct bandgap, in conjunction with its high coefficient absorption [1]
Superior CdTe layer are known to have the sharpest absorption edge which signify lesser impurity energy level and defects as observed from the CdTe layer deposited from the pH2 electrolyte as compared to other layers grown outside this pH range
The bandgap energy of the CCT-CdTe layers grown across the explored pH is within the tolerable range of 1.44±0.03 eV
Summary
II-VI semiconductor material such as Cadmium telluride (CdTe) is well-recognised in the photovoltaic (PV) community due to its optimal and direct bandgap, in conjunction with its high coefficient absorption [1]. CdTe has been identified as one of the possible candidates for achieving highly efficient photovoltaic system in the conventional CdS/CdTe solar cell in the simplest configuration of either an n-p or n-n-Schottky barrier [2]. The growth of CdTe as a layer or incorporated in a CdTebased solar cell in the conventional CdS/CdTe has been performed using electroplating and reported in the literature [3]–[5]. For CdTe, literature on the effect of electrolyte pH value on the characteristic properties of electroplated CdTe is yet to be documented in the literature. The research work focuses on bridging the knowledge gap by exploring the effect of deposition electrolyte pH on the characteristic properties of electrodeposited CdTe thin films
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