Omnidirectional Current Enhancement From Laminated Moth-Eye Textured Polymer Packaging for Large-Area, Flexible III-V Solar Modules
Epitaxial lift-off (ELO) processes have allowed for cheaper development of mechanically ﬂexible, ultra-thin, and high- efﬁciency III-V solar cells. ELO solar cells are natural candidates for applications where solar cells must conform to curved surfaces and provide high efﬁciency and high speciﬁc power generation (W/kg). Such examples include power generation for unmanned aerial vehicles, electric vehicles, and portable electrical power. However, when considering these mobile solar applications, large variations in angle of incidence (AOI) that inevitably occur can greatly decrease overall system efﬁciency due to signiﬁcant Fresnel reﬂections. In this article, we demonstrate the integration of moth- eye antireﬂection nanostructures on the polymer packaging layer of ELO solar cell arrays using a low-cost, colloidal self-assembly process. The moth-eye structures mitigate Fresnel reﬂections and increase photocurrent generation over all measured angles of inci- dence relative to ELO solar cell arrays with traditional untextured polymer packaging. The nanostructures survive a commercial lam- ination procedure, an important criterion that must be met to ensure the feasibility of integration into commercial processing. Outdoor solar characterization measurements are performed and, under direct optical illumination, moth-eye textured solar cell ar- rays show a maximum Isc enhancement of ∼58% at 79° AOI rela- tive to traditional untextured polymer packaged solar cell arrays, and when exposed to both direct and diffuse optical illumination a maximum Isc enhancement of ∼23% at 79° AOI is observed.