Self-assembled nanostructured rear reflector designs for thin-film solar cells

To improve the competitiveness of solar cells, cell efficiency must increase and use of materials must be minimized. Light trapping measures can achieve this by allowing cells to absorb a greater fraction of the incident light. Traditional methods like surface texturing can negatively impact the cell's electrical characteristics and are generally unsuited to thin cell types. A plasmonic light trapping structure that avoids such issues can be formed using self-assembled hexagonal arrays of dielectric nanospheres in a continuous metal layer, at the rear surface of a cell. This can be easily fabricated toward the end of cell production, making it suitable for implementation with various solar cell types. 3D finite-difference time-domain simulations were conducted to investigate the potential of such structures, varying parameters including feature size and spacing, metal and absorber material and thickness, and the impact of random variations in the array. Significant improvements were found for a variety of topographies, with a peak increase in photocurrent from 2 μm silicon of 4.02 mA/cm² or 24.4%, relative to the case of a standard rear mirror with a 100 nm SiO₂ spacer layer. This also compares favorably to arrays of rear metal nanoparticles that previously yielded promising experimental results. We also identified critical parameters to control when designing such structures. A particular advantage of this structure is that it can offer light trapping advantages similar to those provided by metal nanoparticle arrays while still being able to serve as the rear contact of the cell due to the continuity of the metal layer. (Figure presents in abstract)