Double-Side Selective Spectral Response Organic Photodetectors for Demultiplexing Optical Signals

Selective spectral response photodetectors (PDs) capable
of accurately
capturing the color of images have broad applications in industry
and academia. Here, we demonstrate filter-free, wavelength-selective
detection organic photodetectors (OPDs) with two distinct response
ranges and having the planar bilayer heterojunction device structure
by employing either a (semi-)­transparent anode or a cathode as the
incident light window. The resultant OPDs exhibit a responsivity of
51 mA W–1 in the range 300–650 nm and 11
mA W–1 in the range 650–850 nm under top
illumination condition. Similarly, the devices show a responsivity
of 2 mA W–1 for the short-wavelength region and
131 mA W–1 for the long-wavelength region when under
bottom illumination condition, indicating a high responsivity ratio
that meets the requirements for selective detection. Hence, our individual
device not only works in either visible or NIR range but also provides
narrowband detection with spectral widths down to 100 nm in the NIR
range. The working mechanism of spectral selectivity is identified
through quantitative analysis of the external quantum efficiency (EQE)
spectra using optical modeling when compared to the OPDs with bulk
heterojunction structure, thus clarifying the general validity of
the device design concept. Finally, our OPDs can demultiplex intermixed
optical signals from the light-communication system successfully.
Our results should inspire new studies on the device design concept
and new applications of OPDs.