Laser processing in fabrication of Interdigitated Back Contact Silicon Hetero-Junction (IBC-SHJ) solar cell
Date
2015
Authors
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Journal ISSN
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Publisher
University of Delaware
Abstract
The Interdigitated Back Contact Silicon Hetero-Junction (IBC-SHJ) solar cell combines the advantages of high open-circuit voltage of SHJ device and no front electrical shading of IBC device to achieve the very high efficiency potential. Most recently 25.6% IBC-SHJ device has been announced by Panasonic (formerly Sanyo) which is the highest efficiency of single junction photovoltaic device under one sun condition. However, the p and n regions on the rear side of the IBC-SHJ device usually require multi-steps of photolithography process and/or fine photolithography masks, which is very elaborate and not suitable for large scale industrial production. In order to eliminate or reduce the complexity of IBC-SHJ solar cell fabrication, the application of two laser-based patterning processes, namely laser fired contact (LFC) and laser isolation, are being studied in this thesis. Laser fired contacts to n-type crystalline silicon were developed by investigating novel metal stacks containing Antimony (Sb). Lasing conditions and the structure of metals stacks were optimized for lowest contact resistance and minimum surface damage. Specific contact resistance for firing different metal stacks through either silicon nitride or p-type amorphous silicon was determined using two different models and test structures. Specific contact resistance values of 2-7 mΩ cm 2 have been achieved. Recombination loss due to laser damage was consistent with an extracted local surface recombination velocity (SRV) of ~20,000 cm/s that is similar to values for laser fired base contact for p-type crystalline silicon. Both direct laser isolation and laser-chemical isolation were studied as rear side patterning technique for IBC-SHJ cells. Shunt resistance > 5,600Ω cm was obtained by direct laser isolation at the cost of significant surface passivation loss and bulk wafer damage. Shunt resistance > 16,000Ω cm was achieved with laser chemical isolation while lifetime of test structure sample still maintain above 1700 us. The LFC technique together with laser patterning technique has been applied into IBC-SHJ device application. 16.9% IBC-SHJ device has been fabricated and steps of etching steps in photolithography have been reduced and replaced by LFC during process. With mask deposition and LFC technique, 15.2% IBC-SHJ device has been fabricated with no photolithography steps. Finally, p a-Si back IBC-SHJ solar cell was fabricated with laser chemical isolation and LFC. The proof-of-concept device achieved efficiency of 8.8%. The localized base contact technique together with laser patterning technique will enable low cost back contact patterning and innovative designs for n-type crystalline silicon solar cell.