Deactivation Treatments of Silicon Solar Cells for Efficiency Recovery after Illumination Degradation
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1210-Q08-13
Deactivation treatments of silicon solar cells for efficiency recovery after illumination degradation
Teng-Yu Wang1, Terry-Wang1, Yen-Ju Chen2, Chwung-Shan Kou2, Chien-Hsun Chen1, WeiLun Chang1, Sung-Yu Chen1, Chen-Hsun Du1, Wen-Ching Sun1, Chung-Wen Lan1,3 1
Photovoltaics Technology Center, Industrial Technology Research institute, Hsinchu 310, Taiwan, R.O.C. 2 Department of Physics, National Tsing Hua University, Hsinhu 300, Taiwan, R.O.C. 3 Department of Chemical Engineering, National Taiwan University, Taipei 106, Taiwan, R.O.C.
ABSTRACT We applied the deactivation treatments to p-type single crystalline silicon solar cells for deactivating the recombination-active boron-oxygen complex. The methods we used include thermal annealing treatment, capacitively couple plasma (CCP) treatment, and plasma immersion ion implantation (PIII) treatment. The results showed that all the deactivation treatments were working and the energy transfer efficiency (Eff) was thereby increased by more than 1% absolute compared to the degraded state base on the increasing of the open-circular voltage (Voc) and short-current density (Jsc). The CCP deactivated treatment got better efficiencies than PIII treatment because the PIII treatment damaged the surface of solar cells. After the forming gas treatment, the samples could be improved to close to the PIII samples due to the surface damage repairing. However, the increased efficiency could not be kept and would be degraded again after illumination. INTRODUCTION Solar cell is a clean energy resource which can generate electricity directly from sunlight and the p-type (boron doped) single crystalline silicon wafer is most wildly used for solar cells. However, the energy transfer efficiency can not keep stable under illumination [1]. It had been known that the energy transfer efficiency was decayed with the carrier lifetime degraded under illumination due to the recombination of active boron-oxygen complex [2]. Schmidt et al. developed a defect reaction model to describe the formation kinetics of the metastable boronoxygen related defect complex [3]. As people know, there were several methods to solve the degradation problem of single crystalline silicon solar cells, including (a) choose other kinds of doping materials. Gallium doped p-type silicon wafers or phosphorous doped n-type silicon wafers will not decay because there is no boron atoms inside a silicon substrate [4,5]; (b) use low oxygen content wafers, such as floating zone (FZ) wafers or magnetic applied Czochralski (MCz) wafers [6]. However, these kind of wafers are much more expensive than commercial silicon wafers; and (c) deactivate the boron-oxygen complex by any other suitable treatments [7], which can avoid the light-decay problem.
EXPERIMENT In this study, we used 5-inch boron-doped Czochralski (Cz) Si wafers with a thickness of 200 µm and a resistivity of 3~5 Ω-cm. After saw damage removing and wet chemical cleaning, the wafers were textured with random pyramids in a KOH/isopropanol solution. A single-st
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