Researchers from German research center ISC Konstanz and the Delft University of Technology (TU Delft) in the Netherlands have fabricated an interdigitated back contact (IBC) solar cell with a new patterning technique for structuring the rear side of the device.
“Interdigitated back contact (IBC) architecture can yield among the highest silicon-wafer-based solar cell conversion efficiencies,” the research's corresponding author, Vaibhav Kuruganti, told pv magazine. “Since both polarities are realized on the rear side, there is a definite need for a patterning step. Some of the common patterning techniques involve photolithography, inkjet patterning and laser ablation. In our work, we introduced a novel patterning technique using the enhanced oxidation characteristics under the locally laser-doped n++ back-surface field (BSF) regions.”
The BSF regions create energy-band bending that aids in the separation of electrons and holes. They are very useful in giving the extra push needed for electron-hole separation in this remote region.
The research group used a phosphosilicate glass (PSG) layer as a precursor layer for the formation of local heavily laser-doped n++ BSF regions. It deposited the PSG layer via POCl3 diffusion, which is the standard method for industrial n-type emitter fabrication.
The scientists said that the laser-doped n++ BSF regions exhibited a 2.6-fold increase in oxide thickness compared to the non-LD n+ BSF regions after undergoing high-temperature wet thermal oxidation.
“This phenomenon can be attributed to the accelerated oxidation characteristics observed in the phosphorous heavily laser-doped regions with high surface concentrations,” said Kuruganti. “The utilization of oxide thickness selectivity serves two purposes in the context of the IBC solar cell. Firstly, it is employed for the patterning of the rear side of the cell. Additionally, the remaining oxide post patterning under the laser-doped n++ BSF region functions as a masking layer during the subsequent high-temperature boron tribromide (BBr3) tube diffusion, which is responsible for the formation of the emitter on the rear and front floating emitter on the front.”
Tested under standard illumination conditions, the solar cell achieved a maximum efficiency of 20.41%, an open-circuit voltage of 656.6 mV, a short-circuit current density of 40.38 A/mAcm2, and a fill factor of 77.39%.
“The utilization of oxide thickness selectivity under laser-doped and nonlaser-doped regions serves two purposes in the context of the IBC solar cell, first patterning rear side and second acting as a masking layer for the subsequent boron diffusion,” the scientists explained.
The cell was described in the study “Structuring Interdigitated Back Contact Solar Cells Using the Enhanced Oxidation Characteristics Under Laser-Doped Back Surface Field Regions,” published in applications and materials science.
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