Emissive Nanoclusters Based on Subnanometer-Sized Au38 Cores for Boosting the Performance of Inverted Organic Photovoltaic Cells

Abstract

In spite of the successful enhancement of the power-conversion efficiency (PCE) in organic bulk heterojunction (BHJ) solar cells by surface plasmon resonance (SPR), the incorporation of several tens of nanometer-sized (25-50 nm) metal nanoparticles (NPs) has some limitations to further enhancing the PCE due to concerns related to possibly transferring non-radiative energy and disturbing the interface morphology. Instead of tens of nanometer-sized metal NPs, here, dodecanethiol stabilized Au nanoclusters (Au:SR, R = the tail of thiolate) with sub-nm-sized Au38 cores are incorporated on inverted BHJ solar cells. Although metal NPs less than 5 nm in size do not show any scattering or electric field enhancement of incident light by SPR effects, the incorporation of emissive Au:SR nanoclusters provides effects that are quite similar to those of tens of nanometersized plasmonic metal NPs. Due to effective energy transfer, based on the protoplasmonic fluorescence of Au:SR, the highest performing solar cells fabricated with Au:SR clusters yield a PCE of 9.15%; this value represents an approximate to 20% increase in the efficiency compared to solar cells without Au:SR nanoclusters.