Abstract
In this research, thin films of tin sulfide (SnS) and zinc sulfide (ZnS)
were prepared by spray pyrolysis technique on glass substrates at different
substrate temperatures and with different molar ratio of precursors in the
spray solution. Thin films heterojunction solar cell was also developed.
Mechanical move based homemade spray pyrolysis technique was used to
prepare the films on glass substrates. A thermal evaporation coating system
was also constructed to make an electrical Ohmic contact for the fabricated
solar cell.
The first part of the research was focused on the study of the
structural, compositional, morphological, surface analysis and optical
properties of the prepared films using appropriate techniques including
XRD, SEM, EDX and AFM. The structural parameters such as grain size
and dislocation density were estimated from X-ray diffraction (XRD)
pattern. The surface morphology of the films was examined using scanning
electron microscopy (SEM) and atomic force microscopy (AFM). The
average grain size and surface roughness were found to increase with
increasing of the substrate temperature. The elements present percentage in
the prepared films were known using the energy dispersive X-ray (EDX)
spectrum, which revealed that the deposited films are almost stiochiometric,
with (Sn/S) atomic percentage of (1.120) and (Zn/S) atomic percentage of
(1.167) for the optimized films.
Optical transmission and absorption spectra were recorded in the
wavelength range 200-1100 nm, and the data were used to calculate the
absorption coefficient and the optical energy band gap. The results of the
optical study indicated that the deposited ZnS films show a high optical
transmittance in the visible and near-infrared region, while SnS show a high
optical transmittance in the near-infrared region .
The study of the structural of the obtained SnS and ZnS films show
that they are strongly dependent on the substrate temperature and it is
observed that the best crystallinity of the films is obtained at the 375 oC
substrate temperature with a molar ratio of 1:2 of the precursors in spray
solution, and 375 oC found to be optimum temperature to prepare the best
ZnS and SnS thin films. The obtained results were discussed in view of
testing the suitability of SnS film as an absorber and ZnS film as a window
for the fabrication solar cell.
The second part of the research was focused on the performance of
heterojunction solar cell with the configuration, ITO/ZnS/SnS/In. The
optimized prepared SnS film was used as an absorber layer for solar cell and
ZnS film used as a window layer for solar cell. Different metallization
schemes were examined for films Ohmic contacts. The I-V characteristics
for indium metal have been found to be fairly linear in the wide range of
applied voltage which indicates good Ohmic contacts behavior. The TLM
treated indium metal contacts are useful for (ZnS, SnS) based devices since
it exhibited better and thermal stable properties as compared to other
examined metal structures for Ohmic contacts. The specific contact
resistance of the indium has also been measured by the TLM and obtained to
be of an order of magnitude lower than that of other metals. The illuminated
current-voltage characteristics were measured to evaluate our fabricated
solar cell device performance. The most important cell parameters, open
circuit voltage (Voc), short circuit current (Ish), maximum voltage (Vmax.),
maximum current (Imax.), fill factor (FF), and the cell efficiency (η) were
determined and compared with the recently reported theoretical analysis
values. The calculated value of the fill factor was found to be (47.8%) and
the efficiency of the cell was found to be (0.71%).