Relationship of Free Surface Area with Oxygen Concentration in Silicon Ingot Grown by Czochralski Method for High Effici
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Relationship of Free Surface Area with Oxygen Concentration in Silicon Ingot Grown by Czochralski Method for High Efficiency Solar Cells Jun-Seong Park, Tae-Hun Shim and Jea-Gun Park∗ Department of Electronic and Computer Engineering, Hanyang University, Seoul 04763, Korea (Received 28 October 2019; revised 30 October 2019; accepted 30 October 2019) The relationship of free surface area with temperature, power, and oxygen concentration in a silicon ingot grown by Czochralski method for solar cells was investigated by simulating the growing process of 4-, 6-, and 8-inch diameter ingots with a 24-inch quartz crucible. It was confirmed that the temperature at auto-temperature-control (ATC) sensor of 4-inch diameter ingot was higher than 6- and 8-inch diameter ingot due to the longer distance between triple point and ATC sensor, i.e., larger area of the free surface. In addition, it was observed that the power consumption for growing 4-inch diameter ingot was greater than 6-and 8-inch diameter ingot because of its smaller heat capacity resulted from smaller charge size. In particular, it was confirmed that the oxygen concentration of 4-inch diameter ingot was lower than those of 6- and 8-inch diameter ingots since the larger free surface area and weaker melt convection led to the lower oxygen concentration in 4-inch ingot. This understanding of the relationship of free surface area with oxygen concentration in a silicon ingot can be applicable directly to control oxygen concentration in growing different diameter of silicon ingots. Keywords: Silicon solar cells, Impurities in crystals, Computer simulation of liquid structure DOI: 10.3938/jkps.77.940
I. INTRODUCTION Solar-cell industry has been growing over the last decades because of its clean and renewable energy using unlimited sunlight. Czochralski (CZ) method has been a very old technique in semiconductor and solar industry to produce a silicon mono crystal ingot. In the CZ method, a mono crystal seed is dipped into silicon melt in a crucible and a mono crystal ingot is grown into upper direction by an optimal temperature control for preventing the loss of mono structure [1,2]. During the growth process for a silicon mono crystal ingot, a quartz crucible which is composed of SiO2 is used for containing silicon melt to minimize the impurities contamination into the silicon melt [3]. Oxygen component in the quartz crucible dissolves inevitably into the silicon melt and is transferred to both a free surface and a solid ingot by 98% and 2%, respectively. In particular, the structures of solar cell continues to develop to increase solar cell efficiency. The passivated emitter rearcontact-cell (PERC) structure prevails in solar industry [4,5]. In PERC cell structure, the lower resistivity of a mono-crystal wafer is required to compensate for the decrease of rear contact area, which induces light induced degradation (LID) problem resulting from high concentration of boron and oxygen [6–11]. Therefore, oxygen ∗ E-mail:
concentration should be lowered to compensate for high concen
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