Solar cells get a boost from bouncing light

By engineering alternating layers of nanometer and micrometer particles, a team of engineers from the University of Minnesota has improved the efficiency of a type of solar cell by as much as 26 percent. These cells, known as dye-sensitized solar cells (DSSC), are made of titanium dioxide (TiO₂), a photosensitive material that is less expensive than the more traditional silicon solar cells, which are rapidly approaching the theoretical limit of their efficiency. Current DSSC designs, however, are only about 10 percent efficient.

One reason for this low efficiency is that light from the infrared portion of the spectrum is not easily absorbed in the solar cell. The new layered design, as described in the AIP's Journal of Renewable and Sustainable Energy, increases the path of the light through the solar cell and converts more of the electromagnetic spectrum into electricity. The cells consist of micrometer-scale spheres with nanometer pores sandwiched between layers of nanoscale particles. The spheres, which are made of TiO₂, act like tightly packed bumpers on a pinball machine, causing photons to bounce around before eventually making their way through the cell.

Each time the photon interacts with one of the spheres, a small charge is produced. The interfaces between the layers also help enhance the efficiency by acting like mirrors and keeping the light inside the solar cell where it can be converted to electricity. This strategy to increase light-harvesting efficiency can be easily integrated into current commercial DSSCs.