Fast Ultrahigh-Density Writing of Low Conductivity Patterns on Semiconducting Polymers

The exceptional interest in improving the limitations of data storage, molecular electronics, and optoelectronics has promoted the development of an ever increasing number of techniques used to pattern polymers at micro and nanoscale. Most of them rely on Atomic Force Microscopy to thermally or electrostatically induce mass transport, thereby creating topographic features. Here we show that the mechanical interaction of the tip of the Atomic Force Microscope with the surface of a class of conjugate polymers produces a local increase of molecular disorder, inducing a localized lowering of the semiconductor conductivity, not associated to detectable modifications in the surface topography. This phenomenon allows for the swift production of low conductivity patterns on the polymer surface at an unprecedented speed exceeding 20 $\mu m s^{-1}$; paths have a resolution in the order of the tip size (20 nm) and are detected by a Conducting-Atomic Force Microscopy tip in the conductivity maps.Comment: 22 pages, 6 figures, published in Nature Communications as Article (8 pages

Improving the layer morphology of solution-processed perylene diimide organic solar cells with the use of a polymeric interlayer

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On the role of temperature in the triplet-fusion induced low-energy photon up-converted delayed luminescence of a solid state composite

Here we present a temperature dependent spectroscopic study of a solution-processed solid state photon up-converting composite. In our work we address the process of low-energy photon up-conversion at low temperatures in the previously studied blend film of the triplet photosensitizer (2,3,7,8,12,13,17,18-octaethyl-porphyrinato) platinum(II)) (PtOEP) mixed with the blue emitter 9,10-diphenylanthracene (DPA). It is found that, in respect to room temperature, at 100 K the spectral integral of the DPA up-converted emission is increased by a factor of two whereas the spectrally integrated PtOEP phosphorescence is increased by a factor of eight. Temperature-dependent PtOEP phosphorescence and DPA up-converted luminescence kinetics are also recorded

Triplet-triplet annihilation-induced up-converted delayed luminescence in solid-state organic composites: Monitoring low-energy photon up-conversion at low temperatures

Hitherto, the role of the enhanced intermolecular interactions and the effect of lowering the temperature on the process of triplet-triplet annihilation-induced up-converted delayed luminescence in solid-state composites systems have remained controversial. Here we address these issues by performing temperature-dependent time-integrated and time-gated luminescence spectroscopic studies on the model photon up-converting solid composite comprising the (2,3,7,8,12,13,17,18-octaethyl-porphyrinato) PtII (PtOEP) sensitizer, mixed with the blue-light emitting 9,10 diphenyl anthracene (DPA) activator. Atomic force microscopy imaging and photoluminescence (PL) spectra confirm that the strength of intermolecular interactions in the DPA:PtOEP system can be tuned by keeping the composite either in its binary or in its ternary form with the use of the optically inert matrix of polystyrene (PS). By diluting DPA:PtOEP in PS, the concentration of the DPA excimeric and the PtOEP triplet dimer quenching sites is reduced and the lifetime of the DPA up-converted PL signal is prolonged to the microsecond time scale. By lowering the temperature to 100 K, the DPA up-converted luminescence intensity increases by a factor of 3, and this is attributed to the increased energetic disorder of the DPA excited states in the PS:DPA:PtOEP ternary system. These findings provide useful guidelines for the fabrication of efficient solid-state photon up-converting organic layers. © 2014 American Chemical Society

All-Solution-Based Aggregation Control in Solid-State Photon Upconverting Organic Model Composites

Hitherto, great strides have been made in the development of organic systems that exhibit triplet-triplet annihilation-induced photonenergy upconversion (TTA-UC). Yet, the exact role of intermolecular states in solid-state TTA-UC composites remains elusive. Here we perform a comprehensive spectroscopic study in a series of solution-processable solidstate TTA-UC organic composites with increasing segregated phase content for elucidating the impact of aggregate formation in their TTA-UC properties. Six different states of aggregation are reached in composites of the 9,10-diphenylanthracene (DPA) blue emitter mixed with the (2,3,7,8,12,13,17,18-octaethylporphyrinato)platinum(II) sensitizer (PtOEP) in a fixed nominal ratio (2 wt % PtOEP). Fine-tuning of the PtOEP and DPA phase segregation in these composites is achieved with a lowtemperature solution-processing protocol when three different solvents of increasing boiling point are alternatively used and when the binary DPA:PtOEP system is dispersed in the optically inert polystyrene (PS) matrix (PS:DPA:PtOEP). Time-gated (in the nanosecond and microsecond time scales) photoluminescence measurements identify the upper level of PtOEP segregation at which the PtOEP aggregate-based networks favor PtOEP triplet exciton migration toward the PtOEP:DPA interfaces and triplet energy transfer to the DPA triplet manifold. The maximum DPA TTA-UC luminescence intensity is ensured when the bimolecular annihilation constant of PtOEP remains close to γTTA-PtOEP = 1.1 × 10-13 cm3 s-1. Beyond this PtOEP segregation level, the DPA TTA-UC luminescence intensity decreases because of losses caused by the generation of PtOEP delayed fluorescence and DPA phosphorescence in the nanosecond and microsecond time scales, respectively

Photocurrent Stimulation in Organic Photodiodes via Electrically Integrated Photon Energy Up-Conversion Organic Layers

The photophysical process of low photon energy up-conversion via triplet-triplet annihilation (TTA-UC) describes the capability of a multicomponent system to exhibit photoluminescence (PL) at wavelengths shorter than the wavelength used for its photoexcitation. Systems exhibiting TTA-UC luminescence are particularly attractive to a broad range of light management applications including sensitization of photodiode devices, activation of photocatalytic systems and photo-stimulation of optogenetic platforms. Particularly for the area of organic solar cell (OSC) and organic photodetector (OPD) devices, TTA-UC offers the possibility to generate photocurrent when low energy photons are interacting with the device, which would be otherwise lost by their transmission through the device photoactive layer. However, to integrate a TTA-UC layer both by optical and electrical means into an organic photodiode device architecture remains challenging. Here we present a methodology that enables the generation of TTA-UC induced photocurrent in OPD devices functionalized with an electrically and optically integrated TTA-UC layer. An interlayer of the organometallic sensitizer of (2, 3, 7, 8, 12, 13, 17, 18-octaethyl-porphyrinato) PtII (PtOEP) is used for extending the absorption profile of a planar OPD heterojunction to the red, thereby allowing for the capture of photons with energies lower than the absorption energy of the heterojunction. Planar OPD heterojunctions are used comprising the 9,10 diphenyl anthracene (DPA) electron donor interfaced with a C60 fullerene acceptor. In respect to the DPA/C60 reference system, a 7-fold enhancement is achieved in the photocurrent of the PtOEP/DPA/C60 device when photons of 532 nm are used. In addition, the electrical integration of the PtOEP interlayer in the device structure facilitates an optimum hole extraction thereby generating an open circuit voltage of 500 mV. Time-integrated PL spectroscopy on the fabricated devices confirms the occurrence of the TTA-UC process that manifests in detection of the characteristic DPA luminescence upon laser excitation at 532 nm. The applicability of our methodology to a wider set of materials is demonstrated by replacing the C60 acceptor with bis(8-hydroxy-2-methylquinoline)-(4-phenylphenoxy)aluminum (BAlq), a high-energy gap electron acceptor. Based on these findings we demonstrate TTA-UC sensitized PtOEP/DPA/C60 OPD heterojunctions with responsivity (R), noise-equivalent power (NEP) and specific detectivity (D*) values of R= 610 μA/W, NEP= 40 pW and D*= 5.8 × 109 Jones at 550 nm. We will discuss on the potential utilization of these devices in all-optically ternary logic circuits and TTA-UC sensitized OSC platforms. This work was co-funded by the European Regional Development Fund and the Republic of Cyprus through the Research and Innovation Foundation (Project: EXCELLENCE/1216/0010)

Photocurrent Stimulation in Organic Photodiodes via Electrically Integrated Photon Energy Up-Conversion Organic Layers

The photophysical process of low photon energy up-conversion via triplet-triplet annihilation (TTA-UC) describes the capability of a multicomponent system to exhibit photoluminescence (PL) at wavelengths shorter than the wavelength used for its photoexcitation. Systems exhibiting TTA-UC luminescence are particularly attractive to a broad range of light management applications including sensitization of photodiode devices, activation of photocatalytic systems and photo-stimulation of optogenetic platforms. Particularly for the area of organic solar cell (OSC) and organic photodetector (OPD) devices, TTA-UC offers the possibility to generate photocurrent when low energy photons are interacting with the device, which would be otherwise lost by their transmission through the device photoactive layer. However, to integrate a TTA-UC layer both by optical and electrical means into an organic photodiode device architecture remains challenging. Here we present a methodology that enables the generation of TTA-UC induced photocurrent in OPD devices functionalized with an electrically and optically integrated TTA-UC layer. An interlayer of the organometallic sensitizer of (2, 3, 7, 8, 12, 13, 17, 18-octaethyl-porphyrinato) PtII (PtOEP) is used for extending the absorption profile of a planar OPD heterojunction to the red, thereby allowing for the capture of photons with energies lower than the absorption energy of the heterojunction. Planar OPD heterojunctions are used comprising the 9,10 diphenyl anthracene (DPA) electron donor interfaced with a C60 fullerene acceptor. In respect to the DPA/C60 reference system, a 7-fold enhancement is achieved in the photocurrent of the PtOEP/DPA/C60 device when photons of 532 nm are used. In addition, the electrical integration of the PtOEP interlayer in the device structure facilitates an optimum hole extraction thereby generating an open circuit voltage of 500 mV. Time-integrated PL spectroscopy on the fabricated devices confirms the occurrence of the TTA-UC process that manifests in detection of the characteristic DPA luminescence upon laser excitation at 532 nm. The applicability of our methodology to a wider set of materials is demonstrated by replacing the C60 acceptor with bis(8-hydroxy-2-methylquinoline)-(4-phenylphenoxy)aluminum (BAlq), a high-energy gap electron acceptor. Based on these findings we demonstrate TTA-UC sensitized PtOEP/DPA/C60 OPD heterojunctions with responsivity (R), noise-equivalent power (NEP) and specific detectivity (D*) values of R= 610 μA/W, NEP= 40 pW and D*= 5.8 × 109 Jones at 550 nm. We will discuss on the potential utilization of these devices in all-optically ternary logic circuits and TTA-UC sensitized OSC platforms. This work was co-funded by the European Regional Development Fund and the Republic of Cyprus through the Research and Innovation Foundation (Project: EXCELLENCE/1216/0010)

Triplet–Triplet Annihilation-Induced Up-Converted Delayed Luminescence in Solid-State Organic Composites: Monitoring Low-Energy Photon Up-Conversion at Low Temperatures

Hitherto, the role of the enhanced intermolecular interactions and the effect of lowering the temperature on the process of triplet–triplet annihilation-induced up-converted delayed luminescence in solid-state composites systems have remained controversial. Here we address these issues by performing temperature-dependent time-integrated and time-gated luminescence spectroscopic studies on the model photon up-converting solid composite comprising the (2,3,7,8,12,13,17,18-octaethyl-porphyrinato) Pt^II (PtOEP) sensitizer, mixed with the blue-light emitting 9,10 diphenyl anthracene (DPA) activator. Atomic force microscopy imaging and photoluminescence (PL) spectra confirm that the strength of intermolecular interactions in the DPA:PtOEP system can be tuned by keeping the composite either in its binary or in its ternary form with the use of the optically inert matrix of polystyrene (PS). By diluting DPA:PtOEP in PS, the concentration of the DPA excimeric and the PtOEP triplet dimer quenching sites is reduced and the lifetime of the DPA up-converted PL signal is prolonged to the microsecond time scale. By lowering the temperature to 100 K, the DPA up-converted luminescence intensity increases by a factor of 3, and this is attributed to the increased energetic disorder of the DPA excited states in the PS:DPA:PtOEP ternary system. These findings provide useful guidelines for the fabrication of efficient solid-state photon up-converting organic layers