Scientists from the University of New South Wales (UNSW) in Australia have investigated how effectively the laser-assisted firing process developed by Chinese solar module manufacturer Jolywood, the so-called Jolywood Special Injected Metallization (JSIM), enhances the efficiency of industrial-scale TOPCon solar cells by reducing Si-metal contact recombination and have found the manufacturing step can increase cell efficiency by approximately 0.6% absolute compared to the baseline single-step firing process.
“The results show JSIM is readily applicable in large-scale production lines, offering manufacturers a robust pathway to exceed 25% efficiency without significant additional costs or complexity,” the research's corresponding author, Bram Hoex, told pv magazine. “This is particularly relevant for hot, humid climates, aiding industry in achieving bankable, high-efficiency modules.”
The researchers stressed that laser-assisted firing technologies such as JSIM and the so-called laser-enhanced contact optimization (LECO) developed by South Korea-based Qcells comprise an additional laser scanning process combined with an applied reverse bias, after an initial co-firing step. This step is reportedly able to increase the cell efficiency but also significantly improve the corrosion resistance of TOPCon solar cells
In their analysis, the academics compared the performance of JSIM with that of other baseline (BL) single-step co-firing processes. They utilized state-of-the-art cells from the high-volume production of undisclosed solar manufacturers, with the JSIM cells using a homogenous emitter (HE) structure and the BL cells featuring a selective emitter (SE).
Image: Image: UNSW, Progress in Photovoltaics, CC BY 4.0
For the JSIM cells, the research team used a silicon monoxide (SiOx) tunneling layer and a poly-Si layer for the back using plasma oxidation and plasma-assisted in situ doping deposition (POPAID), followed by a buffered oxide etch (BOE) cleaning process. They also used passivation aluminum oxide (AlOx) layers that were deposited via atomic layer deposited (ALD) and silicon nitride (SiNx ) layers deposited through plasma-enhanced chemical vapor deposition (PECVD) on the front side, as well as a PECVD SiNx passivation layer on the rear side.
As for the BL devices, the group utilized a traditional metallization process with a commercial aluminum-silver (Al/Ag) front-screen printing paste and a traditional single-step industrial firing process. “In comparison, the JSIM samples utilized a specialized Ag front finger paste and underwent firing at a temperature about 30 °C lower, followed by the JSIM process, which incorporates a laser line scanning procedure combined with an applied reverse bias,” it further explained.
The analysis showed that the JSIM process enhanced the performance of TOPCon solar cells by around 0.58% absolute. “Detailed quantification of electrical parameters such as contact resistivity, line resistance, and metal contact recombination revealed substantial reductions in front and rear metal short-circuit current density,” Hoex stated. “Comprehensive Quokka 3 simulations validated our experimental findings and highlighted further improvement opportunities, with an additional 0.3% absolute efficiency gain through grid pattern optimization being achievable.”
Looking forward, the researchers aim to optimize the process to improve cell bulk resistivity and surface passivation quality.
Their findings are available in the study “Higher-Efficiency TOPCon Solar Cells in Mass Production Enabled by Laser-Assisted Firing: Advanced Loss Analysis and Near-Term Efficiency Potential,” which was recently published in Progress in Photovoltaics.
Previous research on TOPCon by UNSW showed the vulnerability of TOPCon solar cells to contact corrosion and three types of TOPCon solar module failures that were never detected in PERC panels. Furthermore, UNSW scientists investigated sodium-induced degradation of TOPCon solar cells under damp-heat exposure and degradation mechanisms of industrial TOPCon solar modules encapsulated with ethylene vinyl acetate (EVA) under accelerated damp-heat conditions.
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