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Current optical data storage (ODS) technologies use onephoton-absorption processes to write data by locally changing the optical properties of the medium. [ 1 , 2 ] Since the lateral dimensions of spots that can be written are near the diffraction limit, signifi cant capacity increases require new approaches such as storage in three dimensions. DVDs, which comprise up to four individually addressable storage layers, exemplify the potential of this concept, but the complexity of producing and using multilayer systems increases with the number of layers. In bulk materials, changes can be confi ned in the third dimension via nonlinear optical processes, such as two-photon absorption (TPA). [3][4][5][6] We have developed a novel ODS system that relies on the optically-induced switching of the aggregation state and fl uorescence of a TPA dye in a polymer matrix. Welldefi ned, ∼ 3 × 3 × 6 μ m-large voxels were written with single focused laser pulses and read by confocal laser scanning microscopy. Such ODS systems are easily produced and promise a storage capacity of up to several Tbytes on a DVD-size disk, which is ∼ 100× higher than that of current commercial ODS technologies. [ 6 , 7 ] The optical changes considered for rewritable and write-once read-many three-dimensional (3D) ODS storage media based on TPA include reversible and irreversible photo chemical reactions such as photoisomerizations, [8][9][10] photo-induced dimerizations, [ 11 , 12 ] photodecompositions, [ 13 , 14 ] and photopolymerizations. [15][16][17] Fluorescent photochromic systems have attracted particular interest, because the exploitable photophysical processes are fast, effi cient, and reversible. [18][19][20] However, it has been challenging to create fl uorescent photochromic materials, which combine high stability, high fl uorescence quantum yield, and large TPA cross-section. We here demonstrate a novel approach to 3D ODS materials, which relies on the switching of the aggregation state of an excimer-forming fl uorescent dye with an appreciable TPA cross-section in an inert host polymer.We have previously reported a range of materials, which change their fl uorescence and/or absorption properties upon exposure to heat, [21][22][23] chemicals, [ 24 ] or mechanical forces, [25][26][27] on account of reversible or irreversible stimulusinduced changes of the aggregation state of the dye molecules. We surmised that such changes could be induced in small volumes by TPA-induced local heating and therefore explored a melt-processed blend of poly(ethylene terephthalate glycol) (PETG) and 1.1% w/w of 1,4-bis( α -cyano-4-octadecyloxystyryl)-2,5-dimethoxybenzene [ 22 , 23 ] (C18-RG, Figure 1 a) as TPAaddressable ODS medium. C18-RG was selected on account of its signifi cant changes in absorption and emission spectra upon aggregation/dissociation, its high thermal and photochemical stability, and, as demonstrated here, its appreciable TPA cross-section. PETG was chosen as the matrix due to its glassy nature and transparency in the relevant op...

For example, by systematically varying the thickness of the photoactive region (a tedious process), optical cavity modes that serve to enhance absorption can be tuned in frequency. [ 16 ] Furthermore, as we show here, optical transfer matrix simulations can be used to expeditiously optimize photocurrent generation in the photoactive region by shaping its absorption spectrum. In this contribution, transfer matrix calculations are shown to effectively guide OPV performance enhancement by spectral tuning in inverted polymer photovoltaic architectures.Since both donor and acceptor materials in the active layer contact both electrodes in BHJ cells, interfacial layers (IFLs) are typically introduced to minimize leakage currents. [ 17 ] In conventional OPV device architectures, where holes are collected at the transparent indium tin oxide (ITO) anode and electrons at the refl ective metal cathode, the archetypical IFL deposited on the ITO is the hole transport layer poly(3,4-ethylenedioxyle nethiophene):poly(styrenesulphonic acid) (PEDOT:PSS). However, this layer limits device lifetime since it is corrosive, [ 18 ] hygroscopic, [ 19 ] and thermally unstable, [ 20 ] motivating alternative IFL materials strategies. Thus, an inverted device architecture (Figure 1 ), where ITO collects electrons and a high work function metal electrode collects holes, has proven very effective in enhancing both OPV performance and durability. [ 21,22 ] In the present work, an electron transport layer (ETL) coating is deposited on the ITO cathode. Solution deposited zinc oxide (ZnO) is a particularly effective ETL in inverted OPVs due to its large bandgap, [ 23 ] high electron mobility, [ 24 ] solar transparency, [ 25 ] and well-positioned conduction band energy for use with electron acceptors, such as fullerene derivatives. [ 26 ] While recent literature has demonstrated higher PCEs using a polymeric ETL in the inverted OPV architecture, [ 27 ] sol-gel ZnO is inexpensive, environmentally friendly, [ 28 ] and a common ETL in inverted OPVs, motivating this study on its impact in optical cavity strategies. [ 29 ] In addition to its favorable ETL properties, ZnO has also been used as an optical spacer [ 30 ] when adjacent to the refl ective metal electrode, improving the distribution of optical intensity in conventional OPVs. In contrast, this work describes the very signifi cant consequences for the optical intensity distribution of placing a ZnO layer adjacent to the transparent electrode in inverted architecture OPVs.The inverted device architecture in this work utilizes a ZnO ETL and a BHJ active layer composed of the donor poly [[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl] [3-fl uoro-2-[(2-ethylhexyl)carbonyl] thieno[3,4-b]thiophenediyl]] (PTB7) and the acceptor [6,6]-phenyl C 71 butyric acid methyl-ester (PC 71 BM; Figure 1 ). The PTB7:PC 71 BM active layer has been previously shown to yield large internal quantum effi ciencies and exhibit absorption across much of the visible spectrum. [ 31,32 ] Furthermore, this a...

3D Optical data storage is demonstrated in co‐extruded multilayer films using organic materials. Co‐extrusion is able to produce films on a much larger scale at a much lower cost than current methods. The material compatibility and mechanical flexibility allow for new data formats with higher capacities to be realized.

Concentration of light and infrared capture are two favored approaches for increasing the power conversion efficiency (PCE) of photovoltaic devices. Using optical transfer matrix formalism, we model the absorption of organic photovoltaic films as a function of active layer thickness and incident wavelength. In our simulations we consider the absorption in the optical cavity formed by the polymer bulk heterojunction active layer (AL) between the aluminum cathode and indium tin oxide (ITO) anode. We find that optical absorption can be finely tuned by adjusting the ITO thickness within a relatively narrow range, thus eliminating the need for a separate optical spacer. We also observe distinct spectral effects due to frequency pulling which results in enhanced long-wavelength absorption. Spectral sculpting can be carried out by cavity design without affecting the open circuit voltage as the spectral shifts are purely optical effects. We have experimentally verified aspects of our modeling and suggest methods to improve device design.

† Electronic supplementary information (ESI) available: Synthetic procedures, description of methods, X-ray diffractograms, thermal characterization and optical characterization data, and complete ref. 5 and 9. See

No abstract

Most approaches to high-capacity 3D optical data storage (ODS) require confinement of the writing action to a specified depth in the writing medium. This is achieved by a nonlinear photoresponse, usually two-photon absorption, which requires a pulsed long-wavelength source. Fluorescence photobleaching of a dye/polymer composite can be used at a short wavelength to store data at the diffraction limit in a layered storage medium. In this work, the writing response of a bleachable dye/polymer system illuminated with single pulses of various duration obtained from a modulated 405 nm wavelength CW laser was studied. A transition from a linear to nonlinear writing mechanism was observed near the microsecond time scale. Concentration-dependent measurements indicate that a photothermal mechanism accounts for the nonlinear response in the short pulse, higher power regime. This nonlinear response may be useful for realizing terabyte scale ODS in multilayered polymer media.