Papers by Author: S.R.P. Silva

Abstract: Organic-inorganic photovoltaic systems which attempt to integrate benefits of both material types in terms of ease of fabrication, stability and efficiency are reviewed. Three broad categories; inorganic-small molecule systems, carbon naotube incorporated organic photovoltaics and nanostructured organic surfaces-based photovoltaics have been discussed with reference to recent literature. Nanocrystal-organic systems are designed to improve broadband photon collection possibilty, nanostructred organic surfaces-based systems attempt to enhance exciton dissociation at the increased area interface. Incorporation of carbon nanotubes in donor-acceptor type photovoltaic systems have been shown as a technique to mitigate drawbacks from short carrier diffusion lengths of organic materials. The concepts present new opportunities for complex photovoltaic systems, which need to be cheap, large area and efficient in order to arrive at an economically viable level for mass uptake.

Abstract: Excimer lasers have been utilized for the crystallization of hydrogenated amorphous silicon for electronic applications. These lasers typically operate in the ultraviolet and hence photons are absorbed by the silicon thin films within a few nanometres of the surface, melting and solidifying the silicon on a nanosecond timescale, often without affecting the underlying substrate. This technique enables the use of inexpensive substrates, such as glass, which are highly preferable for low cost, large-area electronic devices. The depth of crystallization becomes important for applications such as photovoltaics, which depends on a number of factors; with laser beam shape one of the most significant. A Gaussian beam profile has been reported to be best suited for controlled evolution of hydrogen during crystallization with minimum surface damage. Previous reports show the typical energy densities of crystallization, comparing the crystalline volume and surface roughness of the resultant films for different film thicknesses. We report significant reductions of laser energy densities for crystallization by modifying the Gaussian pulse profile, while retaining the controlled evolution of hydrogen from hydrogenated amorphous silicon films. An asymmetrical, shorter pulse profile retains the desirable gradual leading edge of the Gaussian pulse for controlled evaporation of hydrogen, while increasing the peak energy. The resultant films show increased surface roughness along with higher crystalline volumes, which may be beneficial for photovoltaics.