Ternary Bulk Heterojunction Solar Cells: Addition of Soluble NIR Dyes for Photocurrent Generation beyond 800 nm

Abstract

The incorporation of a <i>tert</i>-butyl-functionalized silicon 2,3-naphthalocyanine bis­(trihexylsilyloxide) dye molecule as a third component in a ternary blend bulk heterojunction (BHJ) organic solar cell containing P3HT (donor) and PC₆₀BM (acceptor) results in increased NIR absorption. This absorption yields an increase of up to 40% in the short-circuit current and up to 19% in the power conversion efficiency (PCE) in photovoltaic devices. Two-dimensional grazing incidence wide-angle X-ray scattering (2-D GIWAXS) experiments show that compared to the unfunctionalized dye the <i>tert</i>-butyl functionalization enables an increase in the volume fraction of the dye molecule that can be incorporated before the device performance decreases. Quantum efficiency and absorption spectra also indicate that, at dye concentrations above about 8 wt %, there is an approximately 30 nm red shift in the main silicon naphthalocyanine absorption peak, allowing further dye addition to contribute to added photocurrent. This peak shift is not observed in blends with unfunctionalized dye molecules, however. This simple approach of using ternary blends may be generally applicable for use in other unoptimized BHJ systems towards increasing PCEs beyond current levels. Furthermore, this may offer a new approach towards OPVs that absorb NIR photons without having to design, synthesize, and purify complicated donor–acceptor polymers