The role of scale in light management
Light trapping has long been achieved in wafer-based solar cells using 2- to 10-pm pyramidal structures etched into the cell's surface. Using this micron-length scale technology is obviously out of the question in thin-film structures. Light trapping has long been achieved for thin film cells by forming wavelength-scale texturing on a substrate and then subsequently depositing the thin-film cell. This substrate-texturing approach also becomes problematic as cells are made thinner in an effort to save absorber material cost, since it affects cell morphology and back surface recombination.52 Nanotechnology adds to these tools which are available for light management in solar cells. As discussed in Chapter 2, it makes possible two new approaches: photonic structures and plasmon-ics. Both have already been shown to improve cell performance, as discussed in Chapter 2. Both involve nano-scale structures and therefore can be compatible with the thinner devices.