Design of porous silicon antireflection coatings for silicon solar cells

A porous silicon (PS) layer formed electrochemically in the outer part of the n+ emitter of p-n+ Si junctions can be used as an efficient antireflection coating (ARC). A two-step procedure is presented which can determine the electrochemical parameters leading to the formation of an optimized single-layer PS ARC. Single-layer PS ARCs achieving ≈7% effective reflectance between 400 and 1000 nm are obtained on shallow p–n+ junction solar cells. To reduce the reflectance further, the design of double-layer ARCs based on PS is investigated. PS layers with different porosities can be realized in a single experiment by modulating the current density during the electrochemical process. It is shown theoretically and experimentally that such PS structures can lead to an effective reflectance below 3%.