Device architectures for enhanced photon recycling in thin-film multijunction solar cells

Abstract

Multijunction (MJ) solar cells have the potential to operate across the entire solar spectrum, for ultrahigh efficiencies in light to electricity conversion. Here an MJ cell architecture is presented that offers enhanced capabilities in photon recycling and photon extraction, compared to those of conventional devices. Ideally, each layer of a MJ cell should recycle and re-emit its own luminescence to achieve the maximum possible voltage. This design involves materials with low refractive indices as interfaces between sub-cells in the MJ structure. Experiments demonstrate that thin-film GaAs devices printed on low-index substrates exhibit improved photon recycling, leading to increased open-circuit voltages (V oc), consistent with theoretical predictions. Additional systematic studies reveal important considerations in the thermal behavior of these structures under highly concentrated illumination. Particularly when combined with other optical elements such as anti-reflective coatings, these architectures represent important aspects of design for solar cells that approach thermodynamic efficiency limits for full spectrum operation.