Stealthy Hyperuniform Surface Structures for Efficiency Enhancement of Organic Solar Cells

Abstract

Low absorption in the thin active layer of conventional organic solar cells limits their power conversion efficiency. Structured surface layers are a common approach to diffracting incoming light, thus elongating its path through the active layer, thereby increasing the probability of absorption and hence the power conversion efficiency. While standard periodic structures diffract light into discrete angles, making them optimal only for specific wavelengths, random structures induce broadband, but nontailorable diffraction. Thus, instead, a stealthy hyperuniform structure, designed to exhibit beneficial diffraction properties is implemented: it directs the light into a predefined range of higher angles, prevents diffraction into small angles, and is thus ideal for a strong active path length enhancement. After numerical optimization of the feature height and diameter, the stealthy hyperuniform structure is fabricated in silicon by electron beam lithography and subsequently transferred into a transparent polymer via replica molding. Experimental diffraction images reveal a circular symmetric spectrum, inducing diffraction independent of the azimuthal angle and polarization of the incident light. The application of the stealthy hyperuniform structure on a poly[(2,6‐(4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)‐benzo[1,2‐b:4,5‐b′]dithiophene))‐alt‐(5,5‐(1′,3′‐di‐2‐thienyl‐5′,7′‐bis(2‐ethylhexyl)benzo[1′,2′‐c:4′,5′‐c′]dithiophene‐4,8‐dione)]:3,9‐bis(2‐methylene‐(3‐(1,1‐dicyanomethylene)‐indanone))‐5,5,11,11‐tetrakis(4‐hexylphenyl)‐dithieno[2,3‐d:2′,3′‐d’]‐s‐indaceno[1,2‐b:5,6‐b′]dithiophene organic solar cell leads to a sharp increase in current density and power conversion efficiency.