Scientists at the National Renewable Energy Laboratory (NREL) are studying a phenomenon that seems somewhat paradoxical – how certain defects in silicon solar cells may improve, not hinder, the cells' overall performance.
According to Pauls Stradins, principal scientist and project leader of the silicon PV group at NREL, the laboratory's most recent findings contradict conventional wisdom.
Although deep-level defects have been found to hamper the efficiency of solar cells, NREL's results suggest that defects with properly engineered energy levels can improve carrier collection out of the cell, or improve surface passivation of the absorber layer.
NREL researchers ran simulations to add impurities to layers adjacent to the silicon wafer in a cell – namely, they introduced defects within a thin tunneling silicon dioxide layer that forms part of ‘passivated contact’ for carrier collection and, also, within the aluminum oxide surface passivation layer next to the silicon cell wafer. In both cases, these defects were found to be beneficial.
The research by Stradins, Yuanyue Liu, Su-Huai Wei, Hui-Xiong Deng and Junwei Luo, entitled ‘Suppress carrier recombination by introducing defects: The case of Si solar cell,’ appears in Applied Physics Letters.
More research is needed to determine which defects would produce the best results.
The research was funded by the U.S. Department of Energy's SunShot Initiative as part of a joint project with Georgia Institute of Technology, Fraunhofer ISE and NREL to develop a record efficiency silicon solar cell.