Photoactive Molecular Junctions Based on Self-Assembled Monolayers of Indoline Dyes

Abstract

We demonstrate the feasibility of a photodetector based on an ensemble molecular junction, where a self-assembled monolayer of an organic donor-acceptor dye is directly sandwiched between two electrodes. In such a device, upon photoexcitation and generation of a charge-transfer state on the molecule, charges are dissociated and directly collected at the electrodes without the need of transport through a bulk phase, as in usual photodetectors. We show that the device can work in photovoltaic regime and the spectral response can be tuned by varying the light absorbing dye. Therefore, the electro-optical properties of the downscaled device can be unambiguously related to the physical-chemical properties of the molecules, a commonly difficult point to demonstrate in a molecular junction device, because of the uncertainties of the interplay between molecules and electrodes. The proposed device, which relies on a simple self-assembly process, has a strong potentiality for fast responding, downscaled detectors, ultimately limited by charge dissociation dynamics, and can be considered also as a useful tool to investigate fundamental electro-optical processes in molecular monolayers.

Advanced Nonvolatile Organic Optical Memory Using Self-Assembled Monolayers of Porphyrin–Fullerene Dyads

“…The shape of the UV–vis spectrum of the desorbed dyad matched the spectrum of the pristine material in solution (Figure S1). Using the dyads’ extinction coefficients in mesitylene solutions (487 807 M –1 cm –1 for FP-dyad and 568 948 M –1 cm –1 for PF-dyad at 420 nm, according to our calibration) and the measured absorbance, the molecular density of the dyads adsorbed on AlO x was estimated to be about 7.4 × 10 13 molecules per cm 2 , which is comparable with the literature values reported for carboxylic acid induced monolayers adsorbed on TiO 2 and AlO x surfaces. , We therefore conclude that the adsorbed layer is likely to have a density in the order of a monolayer …”

“…Using the dyads' extinction coefficients in mesitylene solutions (487 807 M −1 cm −1 for FP-dyad and 568 948 M −1 cm −1 for PF-dyad at 420 nm, according to our calibration) and the measured absorbance, the molecular density of the dyads adsorbed on AlO x was estimated to be about 7.4 × 10 13 molecules per cm 2 , which is comparable with the literature values reported for carboxylic acid induced monolayers adsorbed on TiO 2 and AlO x surfaces. 40,41 We therefore conclude that the adsorbed layer is likely to have a density in the order of a monolayer. 41 To evaluate the uniformity of the absorbed on AlO x molecular layers of PF-and FP-dyads, scattering-type scanning infrared nearfield optical microscopy (IR s-SNOM, Neaspec, Germany) has been applied.…”

Quasi Two-Dimensional Dye-Sensitized In2O3 Phototransistors for Ultrahigh Responsivity and Photosensitivity Photodetector Applications

“…The second mechanism is photon absorption by the D102 layer followed by electron transfer from the lowest unoccupied molecular orbital (LUMO) of D102 (−2.59 eV) to the conduction band (CB) of In 2 O 3 (−3.98 eV eV). ,, Based on the materials energetics, the latter process is indeed favorable and is expected to increase the electron concentration within the device’s ultrathin channel. This process is expected to shift the V on toward more negative gate voltages and/or increase the off-current of the transistor, in qualitative agreement with the data shown in Figures f and h, where D102-sensitized transistors exhibit an enhanced off-currents when measured under green and blue light illumination.…”

Organic photodetectors based on supramolecular nanostructures

“…Alongside traditional crystalline 1D and 2D nanostructures introduced above which are physisorbed on the substrate surface, the formation of self‐assembled monolayers (SAMs) via covalent surface functionalization represents another powerful tool to integrate an optoelectronic functionality in working devices. Caranzi et al 32 demonstrated the possibility to fabricate a molecular junction‐based photodetector by sandwiching a SAM of indoline dyes between transparent poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) and aluminum electrodes. The carboxylic acid group exposed on indoline dye molecules can be chemically linked to the native Al 2 O 3 layer coating the aluminum bottom electrodes.…”