Low-Temp Thin Film Production with Laser Doping
Written by Sandra Henderson 19 December 2013
US thin-film technology company Natcore Technology is developing new solar cell processes and structures that will allow them to rapidly and inexpensively manufacture high-performance silicon solar cells at low temperatures, without vacuum equipment and with only a few process steps. The process involves texturing the wafers to form a black silicon antireflection surface, passivating the silicon surface and using laser doping to form localised emitter and base contacts.
“We are investigating silicon solar cell structures with localised laser-doped contacts on both the front and rear surfaces as well as device structures with all contacts on the rear surface,” reports Dr David Carlson, a member of Natcore’s Science Advisory board. The company’s black silicon process can be used on the front surfaces of both types of device structures to produce an antireflection surface.
On account of Carlson, Natcore’s novel laser process “utilises a nanosecond green fibre laser where the laser pulse is shaped as a function of time allowing us to optimise the doping profiles.” Laser doping is a process that uses the energy in a laser beam to rapidly form a localised contact to a solar cell at room temperature. An ink or paste containing a dopant such as phosphorus is deposited on a passivated silicon wafer, and the laser beam locally melts both the dopant source and the silicon to form a doped contact in less than a millionth of a second.
“Conventional solar cells are processed at high temperatures (greater than 800 degrees Celsius) for several minutes to form the doped contacts, and antireflection layers are deposited using expensive vacuum equipment,” says Carlson, illustrating the benefits of the laser doping process, compared with previous manufacturing techniques. By contrast, Natcore’s new laser doping process can be performed in about 1 second per silicon wafer at room temperature in air. What is more, “Our solar cell processing can be performed with relatively inexpensive equipment in a much smaller manufacturing plant than that required for conventional solar cells.”
Natcore’s technological advance could prove promising for the future of thin-film solar cells. Laser processing can be used to process very thin silicon wafers or even thin silicon films at low cost, since it is a room temperature process that can be performed in air without physically contacting the wafer. “Thus, we are able to handle very thin fragile wafers or films without breakage,” Carlson says.
Solar Novus Today previously reported on Natcore’s record-breaking black silicon solar wafers. Now, Carlson elaborates on how this new laser doping process will integrate with the company’s black silicon materials: “Black silicon allows us to make a high quality textured front surface, which is an excellent low-cost antireflection layer,” the expert says. “Laser doping allows us to make localised contacts to the black silicon surface, and also allows us to make a low-cost, high performance, back-contact solar cell by using black silicon on the front surface with localised laser-doped contacts on the rear.”
Natcore is poised to take the novel laser doping process into the real world, according to their representative: “We believe that we have all the technology required to develop a commercial product within the next two years and may be able to accelerate this process with the appropriate partner,” Carlson says, adding in conclusion that his company is “now positioned to play a major role in the development of the US PV industry and will continue to develop new technologies to assure our success.”
Written by Sandra Henderson, Research Editor Solar Novus Today |
