273 research outputs found
Study on the properties of CuSbSâ‚‚ and CuSbSeâ‚“Sâ‚‚â‚‹â‚“ thin films for photovoltaic and photodetector applications
The photovoltaic (PV) technology is of great interest in the present scenario owing to
renewable energy production from natural resources such as solar light. At present,
the PV technology markedly deals with the solar cells based on single crystalline
Silicon. However, the production cost involved in the single crystalline Si-based solar
cells accelerated the research towards much cheaper materials for a cost-effective
technology. In this aspect, thin film solar cells are of great importance especially
solar cells based on chalcogenide semiconductors without compromising much in the
device performance due to their versatile properties. CuInGaSe2 and CdTe have
come up with conversion efficiencies up to 21.7% and 21.5% which is comparable
with the highest reported efficiency of 25.6% for a single-crystalline Si-based cell.
Nevertheless, the price and inadequacy of In and Ga, as well as the toxicity of Cd,
serves as barriers towards their practical applications. The research was then focused
on other semiconducting materials having earth-abundant, low cost and non-toxic
constituents. Different material systems were studied as a result including the Cubased
compounds such as copper zinc tin sulfo selenide (CZTSSe) and copper zinc
tin sulfide (CZTS). Due to issues such as complex structural polymorphism and
cation stoichiometry of CZTSSe materials also face problems while incorporated as
absorber layers in solar cells.
Copper antimony sulfide (CuSbS2) is a novel chalcogenide semiconductor featuring
suitable chemical and physical properties for being an absorber layer in solar
cells as Antimony preserves the same chemistry as that of Indium and Gallium
due to the similarities in their oxidation states as well as ionic radii. Additionally, CuSbS2 exhibits an optical band gap of 1.5 eV for direct transition, a high
absorption coefficient of 104 cm−1 and Spectroscopic Limited Maximum Efficiency
(SLME) of 22.9% which are some characteristic features required for an ideal photovoltaic
absorber layer. This material has gained intense attention in the scientific
community since it was first introduced by P.K. Nair et al. via heating of Sb2S3
and Cu2S layers. A lot of attempts have been made thereafter towards developing
this material through different physical and chemical methods and subsequently
integrating the same in PV devices. In the majority of the attempts, the conversion
efficiency of the fabricated cells, however, remained very low compared to the
present commercial PV technologies. The highest reported efficiency of a CuSbS2
based solar cell up to date is 3.22% where CuSbS2 was spin-coated using its precursor
ink. In this thesis, we make a strong effort towards understanding different
properties and device performance associated with this material. We used chemical
bath deposition to prepare Sb2S3 thin films onto which the Cu layer was evaporated
followed by heating to form the ternary CuSbS2 phase. The effects of different Cu
thicknesses, heat treatments (rapid thermal processing, conventional vacuum oven
annealing or both at different temperatures durations), were studied in detail on
the semoconducting properties of CuSbS2 for PV applications. The structure, morphology,
chemical composition and optoelectronic properties of the thin film formed
at different conditions were analyzed using various characterization techniques such
as XRD, Raman, SEM-EDX, XPS, UV-Vis spectroscopy, I-V and photocurrent response
measurements. Device applications of the films which showed comparatively
better properties were tested by incorporating them in solar cells as absorber layers.
The best solar cell based on CuSbS2 showed an efficiency of 0.6% for the substrate
p-n configuration, glass/ITO/n-CdS/p-CuSbS2/Ag. To further improve the
efficiency, we alloyed CuSbS2 with selenium solid solution to fabricate quaternary
CuSbSexS2−X. Our assumptions for alloying it with Se was ground on the fact that
incorporation of Se can shift the bandgap of CuSbS2 from 1.5 to 1.2 eV depending on
the Se content for much efficient solar light absorption. The champion cell featuring
the quaternary CuSbSexS2−X as the absorber displayed a conversion efficiency of 0.91%, higher than the CuSbS2 based cells. In addition to the PV device application,
we also explored the capability of the CuSbS2 in optoelectronic applications where
it was tested as a photodetector for a wide range of wavelengths. For the first time
ever, we found that CuSbS2 has great potential as a photodetector as well owing
to its high sensitivity towards detection of different wavelength light. The synthesis
procedure, characterizations, and device applications are explained in detail in different
chapters of the thesis which can be really useful in understanding the distinct
properties of both CuSbS2 and CuSbSexS2−X and towards further optimization to
improve the conversion efficiencies where these compounds are used as absorbers
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