Synthesis and characterization of nanocrystalline CuCl hybrid films for electroluminescent device fabrication.
Alam, Md. Monjarul (2012) Synthesis and characterization of nanocrystalline CuCl hybrid films for electroluminescent device fabrication. PhD thesis, Dublin City University.
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Cuprous (I) chloride (CuCl) is an intensively studied inorganic material, particularly for
its excitonic related linear/nonlinear optical processes. This is due in large measure to
its very large excitonic binding energies (~190 meV) which are much larger than those
of IIIV and IIVI semiconductors resulting in a high stability of the exciton even at room
temperature. Thus CuCl should be an extremely efficient light emitter due to exciton
mediated electronhole recombination.
In this study, CuCl nanocrystals were synthesized, embedded in organic
Polysilsesquioxane (PSSQ) matrices, deposited on a variety of substrates via the spin
coating method and its properties studied optimized for optical and electrical behaviour.
Room temperature Xray diffraction (XRD) confirmed the preferential growth of CuCl
nanocrystals whose average radius size was ≈1422 nm in the (111) orientation.
Scanning Electron Microscopy (SEM) measurements revealed that the average surface
area of the films covered by the CuCl nanocrystals was ≈4060 % of its total surface
area. Atomic Force Microscopy (AFM) revealed that the average roughness of the film
increases with the annealing time.
Room temperature UVVis absorption revealed both Z1,2 and Z3 excitonic absorption
features at ≈368 nm (≈3.37 eV) and ≈377 nm (≈3.29 eV), respectively. Room
temperature photoluminescence (PL) and cathodoluminescence (CL) measurements
exhibit strong emission in the UV region. Electronic transitions of the CuCl hybrid films
were studied using temperature and power dependent PL spectroscopy measurements.
Thermal quenching of the Z3 free exciton PL emission in hybrid films has been
observed. The biexciton emission peak intensity follows a quadratic dependency on
power in the excitation power range <10 kWcm2
. The results obtained for the CuCl
hybrid films are comparable to those of vacuum evaporated and sputtered CuCl films
reported in the literature.
Room temperature electrical characterization and electroluminescence (EL) emission
were investigated using Au/CuCl hybrid film/ITO structures. Field dependent DC
conduction studies exhibit ohmic conduction in the lower field region and electrode limited Schottky emission type conduction for higher field regions. The device showed
bright electroluminescent emission at ~384 nm when subjected to an AC voltage of
about 100 volts peak to peak.
One challenge linked with the use of CuCl is that it is sensitive to moist air, i.e. CuCl is
not stable in ambient conditions; it forms oxyhalides of Cu(II) within a few days of
exposure to air. The ageing effects on CuCl hybrid films were extensively investigated
and this research indicates that the blend of CuCl with an organic material in particular
PSSQ may be a useful interim solution to the degradation of CuCl films.
Proofofconcept pCuCl/nZnO heterojunction diodes were fabricated and their
structural, optical and electrical properties were investigated. XRD measurements
confirm that no intermediate compound forms at the heterojunction. Room temperature
IV characteristics show diodelike behaviour with the values of barrier height and
ideality factor equal to 0.72 eV and 4.6, respectively. This structure could be useful for
photovoltaic cell fabrication, particularly for the blue/UV spectral regions.
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