Enhancement of Photovoltaic Device Performance in Close-Packed Nanowire Excitonic Solar Cells by Förster Resonance Energy Transfer (FRET)

Abstract

Our ability to fabricate close-packed single crystal rutile TiO₂ nanowire arrays with average inter-wire distances of 5-10 nm allows us to create and control FRET-induced coupling effects, which can occur in this distance regime, in this architecture. We explored the use of such coupling to boost the performance of nanowire excitonic solar cells. Using Ru complex triplet dye N719 as the energy acceptor and fluorescent tetra tert-butyl substituted zinc phthalocyanine as the energy donor (see Fig. 1 for molecular structures), we obtained up to a four fold improvement in the quantum yield for red photons in the 660-690 nm spectral range. Similarly, by using a carboxylated unsymmetrical squaraine dye as the energy acceptor and highly fluorescent Nile Red dye as the donor (see Fig. 1 for molecular structures), we obtained 60% increased external quantum yields for photons in the 480-580 nm spectral range. For both systems, the use of FRET broadened spectral coverage and improved light harvesting. In this report, we also develop fundamental design principles in choosing donor-acceptor combinations for high efficiency FRET-enhanced solar cells in nanowire array architectures.