A few hours after Trina Solar revealed that it achieved the world’s highest efficiency for silicon solar cells with a 28.0% efficient device TOPCon-compatible hybrid back-contact solar cell (THBC), Chinese module manufacturer Longi announced that it achieved a higher efficiency of 28.13% with a hybrid interdigitated-back-contact (HIBC) solar cell.
The result was independently confirmed by Germany Institute for Solar Energy Research Hamelin (ISFH).
Longi also said that HIBC-based modules with an efficiency of 26.4% were certified by the US National Renewable Energy Laboratory (NREL). “These breakthroughs in technological capabilities have already translated into a lead in mass production,” the company said in a statement.
Longi outlined details of his HIBC solar cell architecture in a scientific paper published in November. The company said the device combines passivated tunnel contacts, dielectric passivation layers, and both n-type and p-type contacts.
The cell is built on a high-strength half-cut M10 wafer with edge passivation and optimized n-type contacts, produced by a combined process at high and low temperatures. A layer of indium tin oxide (ITO) improves lateral transport, while multilayer coatings of aluminum oxide (AlOx) and silicon nitride (SiNx) reduce surface recombination.
The researchers also reduced the phosphorus doping in the n-type polycrystalline silicon layer to limit the diffusion of the dopant into the wafer. The company’s in situ passivated edge technology enables edge passivation during manufacturing. Additionally, deeply grooved metal fingers and selective ITO etching help prevent leakage between n-type and p-type contacts, while a thicker amorphous silicon layer improves junction coverage and sidewall encapsulation. To reduce contact resistance without compromising passivation, the amorphous silicon layer is crystallized using a pulsed green nanosecond laser.
Longi said the technology can be scaled up for the production of heterojunction solar cells, although additional improvements are still needed to reduce resistance losses in the p-type contact.
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