Synergetic Light Trapping Effects in Organic Solar Cells with the Patterned Semi-Transparent Electrode
The dielectric/ultra-thin metal/dielectric structure has been widely used as the semitransparent electrodes in organic solar cells (OSCs) due to its potential replacement of transparent conductive oxide indium tin oxide. Here, we introduce the dual light trapping structures i.e. the nanopatterned MoO3/Ag/MoO3 (MAM) as anode and short-pitched metallic grating as cathode to cooperatively improve the OSC performance. The optical and electrical properties of the OSCs have been investigated through solving the coupled Maxwell’s and semiconductor equations by the finite-difference method. The results indicate that the optical light absorption of the active layer and the electrical carrier collection have been significantly enhanced after the adoption of the proposed dual light trapping structures. We have unveiled that the optical and electrical improvements are attributed to the synergetic effects of surface plasmon resonance of the grating patterned cathode and scattering effect of the nanopatterned MAM anode. Our results have furhter revealed that the short-pitched metal grating can induce the considerable field confinement due to the mode coupling and hybridization of the surface plasmons in-between the adjacently short-distance metal strips. With the optimized structural parameters of the dual light trapping structure, the power conversion efficiency (PCE) of the OSCs has been substantially enhanced by 39% in comparison with a flat cell. Besides the efficiency improvement, the OSCs with the proposed dual light harvesting structures reveals an alleviated angular dependence of electrical properties as the light is beyond the normal incident angle. Our results contribute to the further development of the ITO-free OSCs and is promising for the semi-transparent optoelectronics.