Color-selective, Coupled J-aggregate/Nanowire Photodetector

Applications

This technology enhances photocurrent in nanowires and can therefore be used to create an absorption multiplexing device. This device allows retention of all the spectral information and intensity from the original light source, with far better fidelity than a single broadband light sensitizer.

Problem Addressed

J-aggregates are clusters of coherently-coupled molecular dyes, and their intense absorptions and ultrafast excited state lifetimes make them useful light sensitizers for absorption multiplexing. However, it has been a challenge to use J-aggregates in optoelectronic devices, due to the difficulty of controlling the formation of aggregates and the low carrier mobility of many J-aggregates in solid state. This technology demonstrates the use of cyanine J-aggregates to color-sensitize a cadmium-selenide (CdSe) nanowire photodetector in three specific, narrow absorption bands via excitation energy transfer. The J-aggregate and nanowire device components are grown in solution and the sensitizing wavelength is switched from blue, to red, to green, using only solution-phase exchange of the J-aggregates with the same underlying device. 

Technology

All light harvesting devices share two steps: 1) a photon is absorbed by a material, generating an excited state, and 2) the excited state dissociates, giving rise to a photocurrent or other charge separation. This technology uses the following strategy: energy transfer from an excited state in J-aggregates to a biased crystalline inorganic semiconductor, thus distributing the light harvesting and charge transport functions between two materials optimized for each role. The J-aggregate dye attenuates 40% of the incident light in a 13nm flim; however, the dye has a low carrier mobility meaning that it cannot conduct current efficiently. Therefore, this design coats the J-aggregate dye around the CdSe nanowire, allowing the dye to pass the electron to the nanowire. The CdSe nanowires used in this study have high crystallinity and Ohmic contacts, which makes them ideal for photocurrent transport (even across a 10 micron gap). 

Advantages

  • Increases retention of spectral information
  • Increases retention of signal intensity
  • Increases overall signal fidelity
  • Allows further study of Frenkel and Wannier Mott excitons