Chaudhari, Sushmita and Dey, Suhash Ranjan
(2018)
Dip coating of Cu2ZnSn(SxSe1-x)4 Absorber Layer for Solar Photovoltaic Applications.
PhD thesis, Indian Institute of Technology Hyderabad.
Full text not available from this repository.
(
Request a copy)
Abstract
Photon absorber layer plays a crucial role in inorganic photovoltaic solar cells. For
achieving high efficiency with less material usage, absorber layer should be a direct
band gap material with large absorption coefficient. Among all direct band gap
inorganic thin film solar cells, CIGS based solar cell has achieved the maximum
efficiency of 22.6% at lab scale. Toxic nature and less availability of its constituents
in earth crust’s limit its large scale utilization, and thus solar cells based on kesterite
mineral structure, like Cu2ZnSn(SxSe1-x)4 (CZTSSe) have gained interest in the
emerging thin-film solar cell research field. Cu2ZnSn(SxSe1-x)4 (CZTSSe), a
quaternary chalcogenide is an appropriate replacement of CIGS and CdTe absorber
layers in thin film single junction solar cell as it is composed of all earth abundant and
non-toxic elements and have direct band gaps which varies from 1.0 eV to 1.5 eV with
large absorption coefficient (~104
cm−1
). It is originated from CuInS2 by isoelectronic
replacement of indium (In) with zinc (Zn) and tin (Sn) and thus have quite comparable
properties like CuInS2 without the presence of toxic and expensive elements.
The main aim of the present research is the fabrication of CZTSSe thin film through
cost-effective and industrially viable solution based non-vacuum dip coating
technique using hydrazine free precursor solution to avoid toxicity and any accidental
harms that are possible during the fabrication process.
After dip coating of the substrate into the precursor solution, heat treatment of dip
coated CZTS precursor film is needed to form CZTS film. Variation in annealing
parameters aids in better control over the composition of individual elements,
morphology and crystallinity of kesterite CZTS thin-films. The ratio of Cu:Zn:Sn:S
present in the precursor film and annealing conditions control the chemical potential
and thus formation enthalpy of CZTS. Chemical potential control is very important in
case of kesterite structure owing to narrow thermodynamics window. To achieve
phase-pure CZTS thin-film, influence of different annealing parameters (temperature,
holding time, annealing rate and atmosphere) on formation of CZTS is studied.
Optimization of annealing parameters result in the minimization of undesired
viii
secondary phases in the as annealed CZTS films and leads to the formation of uniform,
phase-pure CZTS thin film with the required composition through a simple hydrazine
free precursor solution.
In addition, controlling the reaction among Cu-Zn-Sn-thiourea precursors in the
solution is also a major concern in formation of phase-pure CZTS. Thus,
investigations on effects of addition of amount of stabilizing agent triethanolamine
(TEA) on formation of CZTS thin films through dip coating technique have been
carried out. In the proposed work, triethanolamine (TEA) is used as a stabilizing agent
in the precursor solution. The purpose of addition of stabilizing agent is to form a
complex molecule with the metallic precursor to inhibit the reaction among them. As
a result, addition of stabilizing agent controls the rate of reaction and also maintains
the uniformity of the films. But, further addition of higher concentration leads to non-
uniformity and secondary phases. Along with this, due to optimization of annealing
parameters and concentration of stabilizing agent into the precursor solution,
conventional sulfurization step can be avoided and uniform, crystalline films can be
fabricated by annealing the CZTS precursor film in N2 environment.
Furthermore, formation of phase-pure, Zn rich CZTSSe films with S/(S+Se) ~30% by
selenization of dip coated CZTS precursor films in presence of elemental Se powder
is achieved by incorporation of Se into the film.
Actions (login required)
 |
View Item |
Altmetric
Altmetric