Broadband and omnidirectional light absorption enhancement in organic photovoltaics

Organic solar cells (OSCs) are a promising alternative photovoltaic technology to conventional inorganic solar cells due to their cost effectiveness and broad range of application. Despite their flexible design with small molecules, polymer/fullerene and hybrid small molecule/polymer blends, their performance is hampered by limited light absorption due to the mismatch between optical absorption length and charge transport scale, caused by the low charge mobility in organic materials. A key technical development to circumvent this hurdle is a device design to enhance light trapping. Various approaches have been reported including incorporating metal nanoparticles, surface plasmonic structures and a textured substrate template in OSCs to boost light absorption. However, each approach has its own technical limitation for a particular device design. In this application, we propose a unique approach to address this need. This approach is applicable to all OSC designs with broadband and omnidirectional light absorption enhancement.

In this project, we propose a new type of transparent poly(methyl methacrylate) (PMMA)/transparent conducting oxide (TCO) (with low/high dielectric constant) double layer two-dimensional photonic structures to achieve broadband and omnidirectional light absorption enhancement in OSCs, thereby improving short-circuit current density and efficiency. The broadband light absorption in nano-structured OSCs is dependent on the photonic structures and also the selection of the photoactive materials. The project includes theoretical simulation and experimental optimization, organic/electrode interfacial analysis and process integration. The primary focus is on realization of >20% light absorption enhancement in OSCs, compared to a state of the art planar control cell, through simultaneous excitation of horizontally propagating surface plasmon polaritons, localized surface plasmons, waveguide modes and their mutual coupling.