Characterizations of ZnO Nanostructure Based Optoelectronic Devices
Date Issued
2010
Date
2010
Author(s)
Pin, Chen, Cheng
Abstract
Abstract
Renewable energy was attracted more attentions due to the energy crisis in 1970 and environmental issue in the world. There are several critical problems on high conversion efficiency solar cell manufacturing, low reflectivity, multiple band absorption, wide acceptance angle and low carrier recombination, et al. For the past decades, photovoltaic scientists developed the high conversion efficiency crystalline Si based solar cells by manufacturing the periodic rough structures, pyramid, inverted pyramid and honeycomb, et al., using wet etching on the solar cell surface. And, the reflectance could be drastic decreased due to the gradual refractive index in the surface textured devices. However, the wet etching process is hard to control due to the humidity and temperature in the clean room. Another, the size of textured structure is hard to control at the nanoscale. Furthermore, multiple junction solar cells could
produce the higher conversion efficiency compared to the single junction solar cells due to the broad band absorption spectrum. The highest solar cell conversion efficiency was observed in the GaAs based semiconductor. The cost and difficult process result in the smaller market sharing than Si based solar cells. The acceptance angle of
incident light for solar cells is another important issue for absorbing maximum light intensity by daytime. Although solar tracking system could provide the solution for
this issue, it will cause the extra energy consumption. Another key issue for high conversion efficiency is carrier recombination. More carriers which were recombined in the devices will reduce the conversion efficiency. However, shortening the carrier transit paths could possibly decrease the probability of recombination when carrier
transported to the contact electrodes. From the above mentions, we proposed another approach to manufacture the high conversion efficiency solar cells by combining the material of GZO and Si. By the overlapping of band gaps, the characteristic of broad band absorption ranged from
400nm to 800nm is realized in the n-GZO/p-Si heterojunction photodiodes. By the simple and novel technique of silica nanosphere spraying, the enhanced responsivity and wide acceptance angle could be achieved in the nanoparticle coated devices. The wide acceptance angle in n-GZO/p-Si photodiodes is due to the Bragg diffraction effect,
Litterow configuration. This work could have the potential application to solar cells. Furthermore, we investigate the nanostructure n-GZO/a-Si(i)/p+-Si heterojunction
photodiodes by using the self-masked nanosphere lithography. The characteristics of high responsivity and wide acceptance angle are achieved in the nanostructure
photodiodes which is due to reducing surface reflectivity and nanostructure morphology. Moreover, nanostructure photodiodes have shorter transit time compared to planar
photodiodes which is due to the shorter and more transit paths in the nanostructure devices. Nanostructure photodiodes possess the higher photoresponsivity compared to
planar one which is possible due to the lower reflectance and shorter transit time. The n-GZO/a-Si(i)/nanopatterned p+-Si heterojunction photodiodes has the shortest transit
time compared to planar n-GZO/a-Si(i)/p+-Si and n-GZO/nanopatterned a-Si(i)/p+-Si heterojunction photodiodes.
Finally, self-masked nanosphere lithography and nanopatterned photodiodes possessed the enhanced photoresponsivity, wider acceptance angle and shorter transit time compared to the planar photodiodes. They have the potential applications to solar cells.
Subjects
solar cells
photovoltaics
nanosphere
nanostructure photodiodes
photodetectors
Bragg diffraction
acceptance angle and transit time
SDGs
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