Abstract:
At present CdS/CdTe based solar cells have a significant commercial impression due to its lowcost,
scalability, manufacturability and simplicity. Nevertheless, it is essential to elevate the
optoelectronic qualities of CdS and CdTe materials and the interface properties of CdS/CdTe
heterojunction and ultimately the efficiency of the solar cells. In this regard thermal annealing
is one of the key steps to be considered in order to enhance the material and heterojunction
properties. Hence, in this study, the effect of thermal annealing on electrodeposited CdS and
CdS/CdTe heterojunction was investigated.
CdS and CdTe semiconductor layers were potentiostatically electrodeposited on bare fluorine
doped tin oxide (FTO) glass substrates and FTO/CdS respectively using the typical three
electrode electrolytic cell. For both layers, saturated calomel electrode and high purity (99%)
graphite rod were used as reference and counter electrodes respectively. 0.10 mol/L CdCl2 and
0.01 mol/L Na2S2O3 were used as Cd and S precursors respectively to produce CdS thin films
while 1.35 mol/L CdSO4 and 1.0 mmol/L TeO2 were used as Cd and Te precursors respectively
for CdTe. CdS layers were grown at cathodic deposition potential of 660 mV at pH 1.6 and
temperature of 55 °C. Afterwards, one set of electrodeposited CdS samples was conveyed for
fabrication of CdS/CdTe heterojunction. CdTe layers were grown on CdS layers at cathodic
deposition potential of 650 mV at pH 2.3 and temperature of 65 °C. Subsequently, thermal
annealing was carried out for both CdS and CdS/CdTe at three different temperatures; 390, 400
and 410 °C, for each annealing three different time periods; 10, 15, 20 min were considered.
After the process of annealing all the samples were inspected for their optical, electrical and
morphological properties using the techniques of optical absorption spectroscopy, photoelectrochemical
cell and scanning electron microscopy respectively. According to the results,
the optimum annealing conditions which yielded good optoelectronic qualities for CdS and
CdS/CdTe were found to be 400 °C, 15 min and 390 °C, 15 min respectively.
