Record infrared internal quantum efficiency in silicon heterojunction solar cells with dielectric/metal rear reflectors

Inserting a dielectric between the absorber and rear metal electrode of a solar cell increases rear internal reflectance by both limiting the transmission cone and suppressing the plasmonic absorption of light arriving outside of the cone. We fabricate rear reflectors with low-refractive-index magnesium fluoride (MgF ₂) as the dielectric, and with local electrical contacts through the MgF₂ layer. These MgF₂/metal reflectors are introduced into amorphous silicon/crystalline silicon heterojunction solar cells in place of the usual transparent conductive oxide/metal reflector. An MgF ₂/Ag reflector yields an average rear internal reflectance of greater than 99.5% and an infrared internal quantum efficiency that exceeds that of the world-record UNSW PERL cell. An MgF ₂/Al reflector performs nearly as well, enabling an efficiency of 21.3% and a short-circuit current density of nearly 38 mA/cm² in a silicon heterojunction solar cell without silver or indium tin oxide at the rear.