US researchers developed a monocrystalline solar panel based on “mini cells” based on polysilicon on silicon oxide passivating contacts. The module runs on laser light and is said to achieve over 40% light conversion efficiency and 7V open circuit voltage.
“This technology is affordable because it is silicon-based and uses the same processes used in terrestrial cells, such as TOPCon devices, which are based on silicon oxide passivation contacts,” said Paul Stradins, lead author of the study. pv magazine. “The module consists of poly-Si/SiO2 passivated contact mini-cells. These minicells offer remarkably low contact resistance and are suitable for high insolation.”
In the magazine “High voltage monocrystalline Si photovoltaic mini modules are based dust-Si/SiOx passivating contacts for high power laser power conversion,” published Solar energy materials and solar cells, the researchers explained that the panel can be used in applications such as wireless data transmission in special environments or energy transmission in medical implants.
The multi-junction mini-panel is designed with silicon oxide (poly-Si/SiOx) passivated contacts using a very thin SiOx layer of about 1.5 nm. These passivated contacts are used to build mini-cells that are said to offer remarkably low contact resistance and are suitable for high solar irradiance. The minicells are put on the “edge” and packed into modules.
“These minicells can be assembled into micromodules simply by mechanical stacking” said Stradins. “We used 10 cells, but it can be any number. Thus, the voltages in these micromodules can be high while the currents are kept low.
In a solar module, the direct contact of metal from one cell to another enables the free flow of electricity between them while limiting the series resistance by a large contact area. Light penetrates vertically through the narrow edge of the device, and current is collected laterally through large-surface p- and n-type passivating contacts.
According to the researchers, this architecture enables cell current to be collected from the entire “side” area of the minicell, which is significantly larger than the light entry area. “These 10 or more stacks of minicells can be assembled into a larger power beam conversion module of any size,” Stradins further explained. “There is no size limit, it can be measured if necessary, cooling, tabs and power electronics in the back.”
The research team tested the module under approximately 1000 nm illumination and found that the light conversion efficiency exceeded 40% and the open circuit voltage exceeded 7 V. The fill factor was approximately 78%. “Based on the current device results, it is expected that a power transfer of 25 W could be obtained for a 10 cm2 module with a 12 kW laser source at a distance of 1 km,” the researchers said.
According to Stradins, the minicells are manufactured without expensive lithography. “We use mechanically aligned masks for all coating steps, which are easily done with a so-called laser printer,” he said. “The mini cells are also manufactured using the same laser writing process. They remain attached to the wafer and are processed as a complete wafer at all stages, including final metallization. Only then are they removed and assembled into a micromodule. All of this can be automated on the production line.”
