Organic-inorganic hybrid diodes are very promising for solution processing, low cost, high performance optoelectronic devices. Here, we report a high quality p-n heterojunction diode composed of n-type inorganic SbS and p-type organic 2,2',7,7'-tetrakis-(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (spiro-OMeTAD) with a rectification ratio of ∼10 at an applied bias of 1 V. On illumination with visible light (470 nm, 1.82 mW/cm), the current value in our device becomes 8 × 10 times that of its dark value even at a zero bias condition. The estimated responsivity value at zero bias is 0.087 A/W which is so far the highest reported for any organic-inorganic hybrid photodiode, to the best of our knowledge. It also exhibits a fast photoresponse time of <25 ms (instrumental limit). More importantly, our device can also detect visible light with power density as low as 8 μW/cm with a photocurrent density of 1.2 μA/cm and a photocurrent to dark current ratio of more than 8. We also demonstrate that the values of responsivity, short circuit current, and open circuit voltage of the photodetector can be improved significantly using a thin layer of TiO hole-blocking layer. These findings suggest SbS/spiro-OMeTAD heterojuncton as a promising candidate for efficient self-powered low visible light photodetector.
A dipeptide-appended
naphthalenediimide (NDI) is self-assembled
in an aqueous phosphate buffer medium of pH 7.5 to form nanovesicular
structures. Interestingly, these molecules are assembled to form hydrogels
in the presence of glucono-δ-lactone (at pH 4.7) or Ru3+ solution (at pH 4.6). The gel formation is associated with a sharp
morphological change from nanospheres to a nanofibrous network structure,
and this nanofibrous network is responsible to trapping of many solvent
molecules to form hydrogels. These gels and aggregates are well characterized
by different spectroscopic and microscopic tools including UV–vis
absorption and fluorescence spectroscopy, Fourier transformed infrared
spectroscopy (FTIR), X-ray powder diffraction (XRPD), rheological
studies, and high resolution transmission electron microscopic (HR-TEM)
studies. The peptide-appended NDI was found to form J-aggregate as
is evident from the UV–vis absorption studies of the aggregated
species. Upon excitation at 384 nm wavelength, the glucono-δ-lactone-based
hydrogel shows a greenish blue fluorescence, and similar fluorescence
is observed for the aggregates of NDI-appended peptide in aqueous
buffer medium at pH 7.5. The soluble aggregates and both gels (obtained
from the treatment of glucono-δ-lactone and Ru3+)
show wonderful current conduction and photoswitching properties. The
photoconductivity and the gain in photocurrent values are enhanced
in the GDL and Ru3+ mediated gels by several orders. This
indicates that the morphological change from nanovesicles to ordered
network of fibers has an important role in the enhancement of photocurrent
gain in photoswitching experiments.
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