Materials Chemistry and Physics, Vol.191, 145-150, 2017
Investigating the electronic properties of multi-junction ZnS/CdS/CdTe graded bandgap solar cells
The fabrication of multi-junction graded bandgap solar cells have been successfully implemented by electroplating three binary compound semiconductors from II-VI family. The three semiconductor materials grown by electroplating techniques are ZnS, CdS and CdTe thin films. The electrical conductivity type and energy bandgap of each of the three semiconductors were determined using photo electrochemical (PEC) cell measurement and UV Vis spectrophotometry techniques respectively. The PEC cell results show that all the three semiconductor materials have n-type electrical conductivity. These two material characterisation techniques were considered in this paper in order to establish the relevant energy band diagram for device results, analysis and interpretation. Solar cells with the device structure glass/FIDin-ZnSin-CdSin-CdTe/Au were then fabricated and characterised using current voltage (I-V) and capacitance-voltage (C-V) techniques. From the I-V characteristics measurement, the fabricated device structures yielded an open circuit voltage (V-oc) of 670 mV, short circuit current density (upsilon(sc)) of 41.5 mA cm(-2) and fill-factor (FF) of 0.46 resulting in similar to 12.8% efficiency when measured at room temperature under AM1.5 illumination conditions. The device structure showed an excellent rectification factor (RF) of 10(4.3) and ideality factor (n) of 1.88. The results obtained from the C-V measurement also showed that the device structures have a moderate doping level of 5.2 x 10(15) cm(-3). (C) 2017 Elsevier B.V. All rights reserved.
Keywords:Electrodeposition;Buffer layer;Graded bandgap device structures;n-n-n plus Schottky barrier