ZnO thin films for solar cell and lighting applications (Conference Presentation)

Abstract

ZnO can be used as a phosphor that has several applications and uses in the lighting and solar cell fields. ZnO as a host material in combination with various dopant ions with the correct valence state can be used to obtain emissions from the Ultra violet (UV) to the infra-red (IR) wavelength ranges. The major problem that limits solar cells’ efficiency is their insensitivity to the whole solar spectrum which is the so-called spectral mismatch. Therefore, several mechanisms have been explored based on photoluminescence to convert the solar cell spectrum where the spectral response of the solar cell is low to regions where the spectral response of the solar cell is high. For single crystalline silicon (Si) photovoltaic (PV) cells with a rather small semiconductor band-gap (Eg: 1.12 eV, corresponding to a wavelength of ~1100 nm), the transmission loss of the sub-band-gap photons can still amount to about 20% of the sun’s energy irradiated onto the Earth’s surface. For PV cells with a larger band-gap, such as amorphous Si (Eg: 1.75 eV) solar cells, which are limited to absorb sunlight with wavelengths below 708 nm, manifest even higher near infrared transmission losses. Downconversion, up-conversion and downshifting are some of the mechanisms that may be applied to improve the spectral response. Doped ZnO can be used for both down shifting and up-conversion applications, especially for the improvement of solar cell efficiency. ZnO thin films prepared with different methods such as Pulsed laser deposition, chemical bath deposition and spin coating are compared with each other for possible uses in lighting and solar cell applications.