Synthesis and characterization of nanocrystalline CuCl hybrid films for electroluminescent device fabrication.

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.

Name dc:type.qualificationname

phd

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

Dublin City University

Year dc:date.issued

2012

Author dc:creator

• Alam, Md. Monjarul

• Materials
• Thin films
• Nanotechnology
• Microelectronics
• Photonics

Language dc:language

en