Excitation energy transfer from long-persistent phosphors for enhancing power conversion of dye-sensitized solar cells

Abstract

Incorporation of inorganic phosphors to improve the spectral absorption range of a dye-sensitized solar cell (DSSC) is a promising strategy to enhance efficiency beyond 15%. However, only marginal improvements have been achieved so far, which is mainly due to the use of nonoptimized device architecture and the lack of understanding of the energy transfer mechanism. Here we report results of DSSCs employing long-persistence phosphor coupled to the sensitizing dye. Detailed time-resolved photoluminescence measurements suggest that excitation energy is transferred radiatively as opposed to F\orster resonance energy transfer. As a result of efficient energy transfer, large-area solar cells show a 63% increase in the photocurrent density along with a 54% increase in power conversion efficiency. In addition, the device works as a ``nighttime solar cell'' with generation of $52\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{W}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}2}$ power density in the dark. Under short-circuit conditions, the device can output 300 mV for 30 h in the dark.