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Dependence of Properties for Silicon Heterojunction Solar Cells on Wafer Position in Ingot
N. Nakamura, E. Kobayashi, Y. Watabe
Czochralski (Cz), Defects, Heterojunction, Silicon (Si), High Efficiency
Wafer-Based Silicon Solar Cells and Materials Technology
Subtopic: Silicon Solar Cell Improvements
Event: 27th European Photovoltaic Solar Energy Conference and Exhibition
Session: 2BV.6.29
1566 - 1569
ISBN: 3-936338-28-0
Paper DOI: 10.4229/27thEUPVSEC2012-2BV.6.29
0,00 EUR
Document(s): paper


Many researchers point out that wafer quality affects performance of silicon heterojunction (SHJ) solar cells. Especially, in case of n-type wafers, resistivity varies greatly by uneven distribution of dopant concentration derived from phosphorus segregation even in one ingot. In addition, thermal donors (TDs) which mainly exist in top regions of ingots are generated in Si crystals during the Czochralski (CZ) growth process. Resistivity of the top regions was dropped by the presence of many TDs, although the essential resistivity can be obtained by a donor killer annealing (DKA). Besides passivation ability by a-Si:H films was remarkable and the longest lifetime of 5.7 ms was obtained. As a result of evaluation of wafers made from several regions in an ingot, the highest performance of the wafers located in 200 ~ 300 mm below the top of ingots was confirmed. Certified conversion efficiency of 21.11% and open circuit voltage (Voc) of 733.3mV were achieved by fabricating 6-inch SHJ solar cells using these wafers from such positions in an ingot. Furthermore, output power of 302.2W and module efficiency of 18.5% were achieved in a prototype module of a standard residential size comprising these 60 cells.