Flexible Epitaxial Lift-Off InGaP/GaAs/InGaAs Triple-Junction Solar Cells Integrated with Micro/Nanostructured Polymer Film

Abstract

Epitaxial lift-off (ELO) InGaP/GaAs/InGaAs inverted metamorphic triple-junction solar cells are encapsulated with a micro/nanostructured polydimethylsiloxane (PDMS) film. The microprism array (MPA) is realized on the PDMS film to redirect the light incident on the metal grid line to the active area. Subwavelength structures (SWSs) are also introduced onto the PDMS film to suppress the Fresnel optical reflection loss. Triangular and hemicylindrical shapes are considered for the MPA. The optical responses of the two MPAs are calculated by using ray-tracing methods. The triangular MPA performs better than the hemicylindrical MPA in terms of light-redirection efficiency. It is confirmed that 82.0% of the light incident on the metal grid can be harvested by the effect of the triangular MPA and the Fresnel optical reflection loss is reduced effectively by the SWSs. These effects contribute to photocurrent enhancement. The short-circuit current density and power conversion efficiency of the flexible ELO triple-junction solar cells integrated with the micro/nanostructured PDMS film improve by 7.0% and 7.1%, respectively, compared with those of the solar cells without the PDMS film. By using the flexible PDMS film for light management, the flexibility of the ELO solar cells is preserved.