Active Layer-Incorporated, Spectrally Tuned Au/SiO₂ Core/Shell Nanorod-Based Light Trapping for Organic Photovoltaics

Abstract

We demonstrate that incorporation of octadecyltrimethoxysilane (OTMS)-functionalized, spectrally tuned, gold/silica (Au/SiO₂) core/shell nanospheres and nanorods into the active layer of an organic photovoltaic (OPV) device led to an increase in photoconversion efficiency (PCE). A silica shell layer was added onto Au core nanospheres and nanorods in order to provide an electrically insulating surface that does not interfere with carrier generation and transport inside the active layer. Functionalization of the Au/SiO₂ core/shell nanoparticles with the OTMS organic ligand was then necessary to transfer the Au/SiO₂ core/shell nanoparticles from an ethanol solution into an OPV polymer-compatible solvent, such as dichlorobenzene. The OTMS-functionalized Au/SiO₂ core/shell nanorods and nanospheres were then incorporated into the active layers of two OPV polymer systems: a poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCB₆₀M) OPV device and a poly[2,6-4,8-di(5-ethylhexylthienyl)benzo[1,2-<i>b</i>;3,4-<i>b</i>]dithiophene-<i>alt</i>-5-dibutyloctyl-3,6-bis(5-bromothiophen-2-yl)pyrrolo[3,4-<i>c</i>]pyrrole-1,4-dione] (PBDTT-DPP:PC₆₀BM) OPV device. For the P3HT:PC₆₀BM polymer with a band edge of ∼700 nm, the addition of the core/shell nanorods with an aspect ratio (AR) of ∼2.5 (extinction peak ∼670 nm) resulted in a 7.1% improvement in PCE, while for the PBDTT-DPP:PC₆₀BM polymer with a band edge of ∼860 nm, the addition of core/shell nanorods with an AR of ∼4 (extinction peak ∼830 nm) resulted in a 14.4% improvement in PCE. The addition of Au/SiO₂ core/shell nanospheres to the P3HT:PC₆₀BM polymer resulted in a 2.7% improvement in PCE, while their addition to a PBDTT-DPP:PC₆₀BM polymer resulted in a 9.1% improvement. The PCE and <i>J</i>_sc enhancements were consistent with external quantum efficiency (EQE) measurements, and the EQE enhancements spectrally matched the extinction spectra of Au/SiO₂ nanospheres and nanorods in both OPV polymer systems