Citation:Kumarasinghe, K.D.M.S.P.K., De Silva, D.S.M., Pathiratne, K.A.S., Dharmadasa, I.M., Salim, H.I., Abdul-Manaf, N.A., Ravirajan, P. and Balashangar, K. 2015. Growth of CdS and CdTe thin film semiconductors and fabrication of CdS/CdTe solar cells, p. 194, In: Proceedings of the International Postgraduate Research Conference 2015 University of Kelaniya, Kelaniya, Sri Lanka, (Abstract), 339 pp.
Date:2015
Abstract:
Thin films of CdS and CdTe semiconductor materials were electrodeposited onto
glass/fluorine doped tin oxide conducting glass surfaces using a potentiostat/galvanostat
equipped with a three electrode cell. Aqueous electrolytic bath containing CdCl2 and
(NH4)2S2O3 was used for the electrodeposition of CdS thin films. CdTe thin films were
electrodeposited onto glass/FTO/CdS substrates from aqueous solution having high
concentrations of CdSO4 and low concentrations of TeO2 and CdCl2. The
glass/FTO/CdS/CdTe/Cu-Au solar cell devices were prepared by thermal evaporation of Cu
and Au on CdTe surface.
CdS films grown were annealed at ~400 °C for 15 minutes in air and photo-electro chemical
(PEC) cell measurements were performed to identify the electrical conductivity type. Both
as-deposited and annealed CdS layers were identified as n-type in electrical conduction. CdS
thin films were shown enhanced PEC responses upon heat treatment. The respective band gap
values for as-deposited and heat treated CdS were 2.35±0.05 eV and 2.40±0.05 eV which
were close to the band gap of bulk CdS. XRD analysis of as-deposited CdS layers revealed
the presence of hexagonal CdS materials with the major peak arising from (002) plane.
Following the CdTe deposition on glass/FTO/CdS substrate, the surface of CdTe layers were
coated with a 0.1% CdCl2 solution and structures were annealed at ~400°C for 10 minutes in
air. Band gaps for CdTe layers were found to be 1.45±0.02 eV for both as-deposited and
annealed samples which exhibited the band gap of bulk CdTe. There was a little
improvement in cubic (220) and (311) peaks of XRD spectra of annealed CdTe layers
compared to the as-deposited material, but annealing exhibited a small reduction of cubic
phase preferential orientation (111). SEM images showed that CdS and CdTe layers were
fairly uniform. The fabricated solar cell devices showed the efficiency of 2.1% with Voc ~330
mV, Jsc~20 mA cm-2 and FF~33% under the illumination of air mass (AM) 1.5 conditions
(100 mW/cm2, 1 Sun).
