Photovoltaic solar cells are a route towards local, environmentally benign, sustainable and affordable energy solutions.
Antireflection coatings are necessary to input a high percentage of available light for photovoltaic conversion, and
therefore have been widely exploited for silicon solar cells. Multi-junction III-V semiconductor solar cells have achieved
the highest efficiencies of any photovoltaic technology, yielding up to 40% in the laboratory and 37% in commercial
devices under varying levels of concentrated light. These devices benefit from a wide absorption spectrum (300-
1800 nm), but this also introduces significant challenges for antireflection coating design. Each sub-cell junction is
electrically connected in series, limiting the overall device photocurrent by the lowest current-producing junction.
Therefore, antireflection coating optimization must maximize the current from the limiting sub-cells at the expense of
the others. Solar concentration, necessary for economical terrestrial deployment of multi-junction solar cells, introduces
an angular-dependent irradiance spectrum. Antireflection coatings are optimized for both direct normal incidence in air
and angular incidence in an Opel Mk-I concentrator, resulting in as little as 1-2% loss in photocurrent as compared to an
ideal zero-reflectance solar cell, showing a similar performance to antireflection coatings on silicon solar cells. A transparent conductive oxide layer has also been considered to replace the metallic-grid front electrode and for inclusion as part of a multi-layer antireflection coating. Optimization of the solar cell, antireflection coating, and concentrator system should be considered simultaneously to enable overall optimal device performance.