Omnidirectional and Broadband Light Absorption Enhancement in 2-D Photonic-Structured Organic Solar Cells

The effect of 2-D photonic structures on omnidirectional and broadband light absorption enhancement in organic solar cells (OSCs) is analyzed using a combination of theoretical simulation and experimental optimization. The photonic structures in the active layer, with a blend system of poly[4,8-bis[(2-ethylhexyl)oxy] benzo[1,2- b:4,5- b A]dithiophene-2,6-diyl][3-fluoro-2-[(2- ethylhexyl)carbonyl]thieno[3,4- b ]-thiophenediyl]:[6,6]-phenyl-C70- butyric-acid-methyl-ester (PTB7:PC 70 BM), were prepared by the nanoimprint method. It shows that the 2-D photonic structures enable not only broadband but also omnidirectional absorption enhancements in the PTB7:PC 70 BM-based OSCs over a broader angle range of the incident light, leading to >11% increase in the power conversion efficiency, as compared to an optimal planar control cell. A weak angular dependency on light absorption is a unique feature of the photonic-structured OSCs, which is useful for different applications.