Incorporating its proprietary advances in laser-processing technology, scientists atNatcore Technology (TSX-V: NXT; NTCXF.PK) have created a laser-processed, all-low-temperature solar cell. Their latest device does not require temperatures above 350 degrees C for any process step.
This development sets the stage for a marriage between Natcore’s highly specialized laser processing and its black silicon technology. The fruits of that all-low-temperature marriage would include gains in efficiency and significantly lower production costs.
The milestone was accomplished at Natcore’s R&D Center in Rochester, NY. This is one of the first demonstrations of a low-temperature, laser-processed solar cell by anyone. Further, unlike previous attempts, Natcore’s approach makes it uniquely suited to large-scale manufacturing, especially of high-performance all-back contact cells.
Current silicon processing techniques involve temperatures of 850 degrees C (1,562 degrees F) or higher. But Natcore’s process does not entail temperatures above 350 degrees C for any step. 350 degrees C is a common annealing temperature used in industry, whereas exposure to 850 degrees C and above, the temperature typically used for conventional solar cells, requires specialized equipment. For example, processing at the higher temperature is done in some form of a diffusion furnace, the interior of which needs to be fabricated from quartz or other very high-temperature compatible materials like silicon carbide. Natcore’s process eliminates that diffusion furnace altogether.
An independent study had earlier shown that Natcore’s black silicon process should save 23.5% in manufacturing costs by eliminating one furnace from the production process. Combining that black silicon process with Natcore’s highly specialized laser processing will eliminate this second, final furnace, cutting costs yet again.
There are other benefits from low-temperature processing as well.
Eliminating exposures to elevated temperatures preserves the “minority carrier lifetime” of a cell. Maintaining high minority carrier lifetimes means that efficiencies comparable to the efficiencies of cells made with more expensive computer-chip-grade silicon can be achieved with lower-quality and lower-cost solar grade silicon. That, coupled with eliminating the use of high-temperature processing equipment, should enable these efficiencies while also reducing the costs of fabrication.
As their process is refined, say Natcore scientists, a laser-processed cell will significantly increase power output of solar cells while further reducing manufacturing costs. In their latest experiment, for example, the team has achieved an open-circuit voltage greater than 0.6 V, which represents meaningful progress toward their short-term goal of 0.65V. These and other performance metrics from the first cells indicate that, with further refinement, efficiencies equaling or exceeding today’s best commercial cells are achievable.
“Applying a black silicon etch is a very inexpensive antireflective process,” says Chuck Provini, Natcore’s president and CEO. “Laser processing is also relatively low-cost, because it reduces energy and chemical costs associated with the furnace that it replaces. By combining two low-cost, low-temperature processes, Natcore is effecting a paradigm change as to how solar cells are made. We believe that our proprietary technology will be in great demand, and we will move to license it to the right partner as soon as possible.”
The next steps in the development will be to add Natcore’s black silicon antireflection control technology to the front of the cell and to move the front contacts to the back of the cell in what is called an interdigitated contact pattern. Eliminating the front contacts will allow an additional 3% to 4% more light to enter the cell and increase its output by a comparable amount. Natcore will have a unique and proprietary position with this technology.