Flexible solar cells made from another form of silicon, called amorphous silicon, have found a place in niche applications where low weight is critical. However, these cells haven’t come into wider use because they’re much less efficient than the crystalline silicon used in conventional solar cells. There are many groups working on new materials, including polymers for flexible solar cells. But these materials don’t yet match the efficiency and durability of silicon, says Ray Chen, a professor in the microelectronics research center at the University of Texas at Austin. “I can’t say silicon will be the material in the long term,” says Chen. “But based on the data we have at this moment, [monocrystalline] silicon is a very robust material and has the advantage of reliability and efficiency.
A major advantage of making solar-cell arrays using his transfer-printing process, says Rogers, is the ability to control the spacing between the microcells. Sparse arrays of the cells are semitransparent and could be used as tinted, energy-producing window coatings. Rogers also hopes that the thin solar cells will replace conventional solar cells on roofs and in other places where solar cells are already found. If the Illinois technology does prove to be cheaper and easier to transport and install than conventional cells, it could remove some of the barriers to more widespread use of solar power.
Still, questions remain concerning the efficiency of Rogers’s solar cells. To be game changers, these cells will need to have an efficiency closer to 15 percent, says Branz. There are existing methods for increasing the efficiency of monocrystalline silicon solar cells to more than 20 percent, says Rogers, and these methods could be applied to the microcells as well, although the University of Illinois researchers have not yet focused on optimizing the material’s efficiency.