Light concentration in polymer bulk heterojunction solar cells with plasmonic nanoparticles

Abstract

ABSTRACT We investigate the light concentration effect of localized surface plasmon resonance by embedding a layer of silver nanoparticles in the low band gap polymer bulk heterojunction solar cells. Particle electromagnetic interaction is demonstrated by using the 3-dimensional finite-difference time-domain computational method. This nanostructure exhibits broadband optical absorption enhancement and weak dependence on incident light polarization. The optical concentration mechanism is discussed by near-field distributio n analysis. This method can be used to optimize the design of plasmonic organic solar cells for high energy conversion efficiency. Keywords: organic solar cell, bulk heterojunction, low band gap, nanoparticle, surface plasmon, light concentration 1. INTRODUCTION Due to their flexibility, light weight, cheapness, polymer solar cells (PSCs) have attracted more and more attention within the past few years [1]. Their power conversion efficiency is poorer than silicon solar cells, since the typical electron-hole diffusion lengths in PSCs are is about ~20nm, but their active layers are usually required to be ~100nm thick to absorb sufficient sunlight [2]. Although various me thods, such as introducing bulk heterojunction and low band gap materials, have been put forward to alleviate this contradiction, a smaller thickness of active layer with adequate absorption is still quite essential to get higher efficiencies. Up to date, there has been considerable interest in overcoming weak absorption of photovoltaic thin films through plasmonic nanostructures by means of far field scattering, light concentration and surface plasmon polariton [3]. Very recently, some groups have contributed to the experimental research using light concentration [4]. Meanwhile, a systematic electromagnetic modeling is required to interpret the mechanism and further optim ize the light concentratio n in plasmonic PSCs [5].