Hydrothermal synthesis of materials for intermediate band solar cells
Solar energy is an abundant energy source that may provide an environmentally
friendly alternative to fossil fuels. The utilization of the solar energy have so far
been limited by various energy losses in the photovoltaic devices. Intermediate
band solar cells use a three photon absorption process to take advantage of a
larger range of photon energies compared to conventional solar cells, increasing
the maximum eciency of the solar cell. Iron substituted copper gallium disulphide
(CGFS) has been proposed as one of the most promising systems, based
on eciency calculations. Recently a CGFS with promising absorption properties
has been synthesized, suggesting that an intermediate band may indeed be
introduced to the CuGaS2 band gap.
In this thesis, hydrothermal synthesis is used to make a parameter study
of the unsubstituted CuGaS2 to optimize the phase purity. Iron substitution
into the lattice has been attempted and a preliminary study of the reaction
mechanisms has been made. Phase identication of the products has been
made using x-ray diraction (XRD) and the diractograms have been analysed
using Rietveld and Pawley renements to determine phase composition, lattice
parameters and crystallite sizes. The microstructure of the products has been
characterized using scanning electron microscopy (SEM), and energy dispersive
spectroscopy analysis (EDS) has been used to determine the composition of the
dierent microstructures. Reflectance spectroscopy has been attempted to find the
absorption properties of the material.
The major findings are that a parameter combination of 200-250 degrees reaction
temperature, 30 hour reaction time and a copper and gallium precursor concentration
of 0.15M or higher gives the most phase pure product of ca. 95 atomic
percent CuGaS2. Degree of filling of the autoclave was not found to have a
large effect on the product, though extreme fill factors were not tested. It is
suggested that the CuGaS2 crystallites grow by a continuous reaction between
the precipitated secondary phases and the unreacted precursors in the solution.
A reaction temperature above 160 degrees or a reaction time over 1 hour is needed
for nucleation of CuGaS2. Indications of iron substitution into the CuGaS2
lattice by hydrothermal synthesis were found, which has not been previously
reported. The obtained products were not phase pure enough to make accurate
reffinements on lattice positions.
Place, publisher, year, edition, pages
Institutt for kjemi , 2013. , 134 p.
IdentifiersURN: urn:nbn:no:ntnu:diva-21158Local ID: ntnudaim:6919OAI: oai:DiVA.org:ntnu-21158DiVA: diva2:631295
Mathisen, Karina, FørsteamanuensisVullum, Fride