Microcrystalline SiO and its Application to Solar Cell
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0974-CC10-28
Microcrystalline SiO and its Application to Solar Cell Channarong Piromjit, Decha Yotsaksri, Nirut Pingate, and Porponth Sichanugrist Nationnal Science and Technology Development Agency, 111 Thailand Science Park, Paholyothin Rd., Klong Luang, Pathumthani, 12120, Thailand ABSTRACT As microcrystalline silicon oxide (µc-SiO) is reported to be more promising material than microcrystalline silicon carbide for the application to solar cells, both of high efficiency amorphous (top cell) and microcrystalline (bottom cell) silicon solar cells have been developed on tin oxide coated glass substrate by using µc-SiO p-layer and buffer i-layer. High VHF frequency of 60 MHz and carbon dioxide gas are used for their deposition. ZnO is coated on Asahi's type U tin oxide by DC sputtering in order to promote the crystallization of the µc-SiO p-layer. It was found that the top cell with this novel µc-SiO p-layer and the microcrystalline bottom cell with novel µc-SiO p-layer and buffer layer have higher cell efficiency than the one with normal SiO p-layer and µc-Si p-layer, respectively. Up to now, an efficiency of more than 15% has been achieved with a-SiO/a-SiGe/µc-Si tandem cell.
INTRODUCTION Microcrystalline silicon oxide (µc-SiO) was reported to be more promising material than microcrystalline silicon carbide (µc-SiC) for the application to solar cells by author since its microcrystallization could be occurred more easily than µc-SiC [1]. At that time, it was deposited by 13.56 MHz and was applied to the p-layer of nip-type solar cell fabricated on metal substrate. There is no work done after that on pin-type glass substrate. On the other hand, µc-SiC deposited by ECR has been developed and applied to the device fabricated on glass [2]. Higher efficiency was achieved, but its scale up to the manufacturing was somehow difficult. Recently, Mitsubishi Heavy Industries has developed µc-SiC using VHF (Very High Frequency) glow discharge and has applied to the microcrystalline bottom cell [3]. They achieved 8.1% with higher Voc of 0.573 V, but there is no work done with the top a-Si cell. In our present work, we have developed µc-SiO p-layer and buffer layer using VHF and have applied them to top, middle and bottom cells fabricated on the glass substrate for a-SiO/aSiGe/µc-Si tandem type solar cell for the first time.
EXPERIMENT A cluster-type, multi-chamber system has been used to deposit various films such as Ag, ZnO, a-Si, µc-Si and µc-SiO films on 30 cm x 40 cm area without breaking the pressure. Our detailed cell structure for the top cell is glass / SnO2 / ZnO / p(µc-SiO) - buffer i(SiO or µc-SiO)
- i(a-Si) - n(µc-Si) / ZnO / Ag while i(µc-Si) and n(a-Si) were used instead of i(a-Si) and n(µcSi) for the bottom cell (Figure 1). High VHF frequency of 60 MHz, carbon dioxide gas and higher hydrogen dilution are used for µc-SiO deposition. ZnO thin film is deposited on Asahi's U-type tin oxide by DC sputtering in order to promote the crystallization of the µc-SiO p-layer. The thick of the top and bottom cells are fix
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