A novel way to make thin, uniform coatings developed at Rice University could reduce the cost of making conventional silicon solar cells, and could open the way for new kinds of solar cells that are far more efficient or cheaper than conventional ones.
The technology, which deposits coatings in a low-temperature, liquid-based process rather than the high-temperature gas-based process used now, is being commercialized by Natcore Technology, a startup in Red Bank, New Jersey. The company plans to use the technology to replace a standard step in conventional solar cell manufacturing—adding an antireflective coating to silicon wafers to help them to absorb more light. It will also offer a more advanced antireflection technology, called black silicon.
At the same time, Natcore is developing more advanced applications of the process, including fabricating solar cells made of carbon nanotubes or nanoscale crystals called quantum dots. Such solar cells will probably take years to commercialize, but could far outperform conventional solar cells. Nano solar cells have been attempted before, but the company thinks its new manufacturing technology could make them affordable.
As a replacement for high-temperature processes on a conventional manufacturing line, the liquid-based process can lower manufacturing costs. Natcore’s CEO, Charles Provini, estimates that replacing a conventional coating machine with one of his company’s could save a solar manufacturer about $1 million in electricity costs per year.
Manufacturers don’t currently use liquid-based processes for antireflection coatings in part because it’s been difficult to make the coating uniform enough for solar cells. The problem arises from the way a liquid process typically works. The coating forms as reactants in the liquid interact with a surface. As the reactants are used up, the rates of deposition change, resulting in variations in the thickness of the coating. Researchers at Rice addressed this problem by developing a system for continuously replenishing the reactants while also closely monitoring the thickness of the films.
One of Natcore’s advanced nano solar cell designs involves depositing layers of quantum dots on a silicon solar cell. The quantum dots are designed to absorb colors that silicon doesn’t, potentially doubling the efficiency of solar cells. This has been tried before, but forming a layer of quantum dots has required expensive processing technology, and it has proven difficult to space the quantum dots to avoid unwanted electrical discharges between them. The Natcore process is inexpensive, and it provides a means for controlling the arrangement of the quantum dots by coating them with a layer of silicon dioxide that acts as a spacer. The company has decided to start by coating conventional silicon solar cells to make it easier for the industry to adopt the technology, but could eventually do away with silicon wafers for an entirely quantum-dot-based solar cell that uses more than one type of quantum dot to efficiently absorb the entire range of wavelengths in sunlight.