All electrodeposited, multilayer graded bandgap solar cells using II-VI eemiconductors

The aim of this project is to develop high efficiency thin film solar cells with materials grown by one single growth method - electrodeposition. ZnS (Eg = 3.70 eV), CdS (Eg = 2.42 eV), CdTe (Eg = 1.45 eV) and ZnTe (Eg = 2.40 eV) layers were electrodeposited using aqueous solutions to be used as buffer, window, absorber and pin-hole plugging layers respectively in the devices. X-ray diffraction (XRD), optical absorption, photoelectrochemical (PEC) cell measurements, scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to study the structural, optical, electrical and morphological properties of the layers and hence optimise their growth conditions. All the layers showed their expected structural properties and energy bandgap values in agreement with literature values. The electrical conductivity type was confirmed for ZnS, CdS and CdTe as n-type and ZnTe as p-type using PEC technique after growing them on glass/FTO substrates. Solar cells were then fabricated and tested under AM 1.5 illumination conditions. The efficiency of 10.4% was observed (Voc = 640 mV, Jsc = 40.8 mAcm-2, FF = 0.40) for the preliminary devices and the work is progressing for development of the structures by improving growth conditions and processing steps. The materials growth using electrodeposition, characterisation, device fabrication and assessment results are presented in this paper.