Self-contained optical enhancement film for printed photovoltaics

Printed photovoltaics promise lightweight and flexible light harvesting devices for conformal integration into buildings, portable electronics or vehicles. This is enabled by employing thin photoactive layers, which can reduce the use of sometimes costly and scarce absorber materials. Since this in turn comes along with an incomplete light absorption and hence restrains the power conversion efficiency of printed photovoltaics, their development was since long accompanied by integrated light management. However, besides a mere efficiency enhancement, new strategies should consider both functionality and additional costs of the light management. Optical enhancement strategies should consequently avoid complications with the delicate printing of the photovoltaic layers and therefore structures on the light incident surface of the device have been proposed. However, these air-faced approaches are prone to the impacts and stress of operating conditions and hence a protected solution is desired. Here we introduce a carefully designed photonic nanostructure embedded in a self-contained transparent film, which offers a conformal device attachment. An efficiency enhancement of 11% is demonstrated on an organic photovoltaic device. Angle dependent measurements moreover suggest a yearly increase of 13%, exploiting the seasonal asymmetry of the incident solar power by a built-in asymmetric diffraction.