Random and V-groove texturing for efficient light trapping in organic photovoltaic cells

We propose textured plastic films attached to the external surface of the substrates of organic photovoltaic devices (OPVs) as spectrally neutral light trapping schemes. Both randomly textured films and those containing an array of V-grooves are explored from experimental and theoretical perspectives. Randomly textured surface, providing a close approximation to the Lambertian scatterer that increases the total optical path length of the incident light, is shown to yield an enhancement in short-circuit current density (J_sc) as large as 9.3% in polymer:fullerene bulk heterojunction cells. Different from the case of random texturing, V-groove texturing scheme manages the light in a controlled manner yet can still enhance the optical path length upon careful optimization. In particular, a V-groove with the vertex angle of 100.8-112.0 is found to be highly effective as it suppresses the internal rays from escaping the structure. Together with use of highly reflecting Ag electrodes, V-grooves with the optimal vertex angle leads to 15% enhancement in J_sc, improving the efficiency of OPV cells under study from 6.5% to 7.4%.