Performance of Plasmonics Thin Silicon Solar Cell Using In and Ag Nanoparticles on Front and Rear Side

Autor: Chun-Chin Liao 廖俊欽, 廖俊欽
Rok vydání: 2013
Druh dokumentu: 學位論文 ; thesis
Popis: 101
In this work, the indium (In) and silver (Ag) nanoparticles forming on the front- and rear-side surface of thin silicon solar cell, respectively, to enhance photovoltaic performances due to plasmonics effects are reported. When the sunlight incident on the proposed solar cells, indium nanoparticles on the front surface can be enhanced the conversion rate of photons to photon-carriers at short wavelength band and the silver nanoparticles on the rear surface scattered the long-wavelength photons, which contributed by localized surface plasmon. In this study, bare Si solar cell was first fabricated and characterized. The liquid phosphorus source was spun upon on a 200 um-thick P-type silicon substrate and capped with a SiO2 layer. Then heat treated by RTA at 900 oC which the phosphorus atoms can be diffused into p-silicon, forming a p-n junction. The rear side electrode was grid-shape pattern Al electrode (Al coverage of 60 %), deposited by e-beam evaporation and photolithograph processing. Subsequently, Al electrode was annealed at 450 oC in N2 atmosphere for 5 min to make the better ohmic contact. Simililary, the front-side finger Ti/Al electrode was obtained by e-beam deposition and lift-off process. Secondly, 30 nm, 59.5 nm and 85 nm-thick TiO2 space layer are deposited on the fabricated bare cells, respectively, by e-beam evaporation. Before indium film deposited on the TiO2 surface, the TiO2 space layer was annealed at 200 oC in H2 atmosphere for 30 minutes to form a high quality and high density TiO2 space layer. Then 3.8 nm-thick Indium (In) was deposited upon those TiO2 space layer and all samples subsequently annealed at 200 oC in H2 atmosphere for 30 min to obtain indium nanoparticles. The reflection spectrum, external quantum efficiency (EQE) response, and photovoltaic I-V were measure and compared as the cell with and without indium nanoparticles on the TiO2 layer. The results show that the plasmon resonance wavelength of indium nanoparticles was red-shifted as the thickness of TiO2 increase. Under AM1.5 illumunation, the enhancement of the short-circuit current density (Jsc) of the plasmonics solar cells with 30 nm, 59.5 nm and 85 nm-thick TiO2 space layer are 8.29 % (from 25.09 mA/cm2 to 27.17 mA/cm2), 6.85 % (from 30.37 mA/cm2 to 32.45 mA/cm2) and 3.86 % (from 29.01 mA/cm2 to 30.13 mA/cm2), respectively, compare to the cell only with corresponding TiO2 layer. Similiary, the conversion efficiency (η) can be achieved 7.86 % (from 9.41 % to 10.15 %), 6.35 % (from 12.12 % to 12.89 %) and 5.56 % (from 11.51 % to 12.15 %), respectively. Therefore, the plasmonic Si solar cell with indium nanoparticles on the 30 nm TiO2 space layer exhibited the best improving in photocurrent and conversion efficiency. Summary, the totally short-circuit current density output of 27.17 mA/cm2 and conversion efficiency of 10.15 % are obtained in the proposed cell with plasmonics on the front-side surface. Finally, the bare Si solar cell with gride-shap pattern Al-electrode (coverage of 60%) on the rear-side was fabricated. Next, 30 nm-thick silver film was deposited on the rear-side surface and then annealed at 300 oC in N2 atmosphere for 3 min, forming Ag nanoparticles. The short-circuit current density increase of 1.39 % (from 23.10 mA/cm2 to 23.42 mA/cm2) and conversion efficiency increase of 1.54 % (from 9.09 % to 9.23 %) were obtained as the cell only with Ag nanoparticles on the rear-side surface. However, the cell of with metallic nanoparticles on both the front and rear surface, the photocurrent density increase of 8.51 % (from 27.25 mA/cm2 to 29.57 mA/cm2) and conversion efficiency enhanced by 9.78 % (from 10.74 % to 11.79 %) are presented. Therefore, the total short-circuit current density of 29.57 mA/cm2 and the conversion efficiency of 11.79 % were obtained as the thin silicon solar cell with In and Ag nanoparticles on the front and rear surface.
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