A series of new symmetrical donor-acceptor-donor (D−A−D) dyes based on s-indacene-1,3,5,7(2H,6H)-tetraone as an acceptor unit containing varying electron donating moieties and analogous donor-acceptor (D−A) chromophores with indane-1,3-dione as an acceptor are synthesized. By employing these two sets of dyes, the influence of a scaffold change from unsymmetric push-pull (D−A) to symmetrical (D−A−D) systems on optical, electrochemical, and photovoltaic properties are explored. Detailed comparative studies reveal favorable optical characteristics and considerably decreased bandgaps for the D−A−D dyes compared to those of the reference D−A chromophores. Accordingly, the evaluation of the present dyes as donor materials in bulk heterojunction (BHJ) solar cells in combination with fullerene derivatives PC₆₁BM or PC₇₁BM as acceptors afforded significantly improved performance for devices based on D−A−D blends (up to a factor of 4 compared to the respective D-A reference) with power conversion efficiencies of up to 2.8%. In less polar solvents such as toluene, some of the novel D−A−D chromophores exhibit unexpectedly high fluorescence quantum yields Φ_em of up to unity, in striking contrast to their weakly fluorescent D-A counterparts.

Photochromic molecules provide an intriguing and relatively untapped alternative to traditional materials utilized in organic memory devices. Here, we review recent progress in the implementation of photochromic molecules in electrically-addressed organic memory devices. Recent results for a light-emitting photochromic organic diode are highlighted in the context of multifunctional devices with the ability to simultaneously operate as multilevel memory, signage and display elements. Furthermore, a set of design rules for successful implementation of photochromic compounds in organic memory devices are suggested.

1-Bis[4-[N,N-di(4-tolyl)amino]phenyl]-cyclohexane (TAPC) has been widely used in xerography and organic light-emitting diodes (OLEDs), but derivatives are little known. Here, a new series of solution-processable, crosslinkable hole conductors based on TAPC with varying highest occupied molecular orbital (HOMO) energies from −5.23 eV to −5.69 eV is implemented in blue phosphorescent OLEDs. Their superior perfomance compared with the well-known N4,N4,N4′,N4′-tetraphenylbiphenyl-4,4′-diamine (TPDs) analogues regarding hole-injection and mobility, electron and exciton blocking capabilities, efficiency, and efficiency roll-off is demonstrated. Overall, the TAPC-based devices feature higher luminous and power efficiency over a broader range of brightness levels and reduced efficiency roll off. A systematic broadening of the emission zone is observed as the hole-injection barrier between the anode and the hole-transporting layer increased.

Novel azo-containing sol–gel films exhibiting outstanding properties for optical applications via nonlocal photoisomerization gratings were reported recently, although the underlying mechanisms were not well understood, especially regarding the unexpected non-local effect. Here, this photoisomerizable sol–gel material is characterized in-depth, analyzing the design and fabrication strategy, and discussing the aspects that enable the efficient photoresponse, with focus on the holographic recording. The material consists of an azochromophore-rich silica matrix containing glycidoxypropyl groups, which provide increased flexibility and internal free volume for improved dye photoresponse. The matrix characteristics allow a novel procedure for fabrication of thick optical films, in which chromophore aggregation is ruptured by thermal annealing while keeping the material centrosymmetry (beneficial for high hologram contrast). The molecular photo-orientation promotes alignment of microscopic domains in a cooperative motion, not reported previously in sol–gel materials. This collective mechanism enhances the material response and explains some intriguing features of photoisomerization gratings. In particular, there is evidence that spatially shifted domains are related to the grating nonlocal nature. Different recording (write–erase–write) procedures that distinctly affect the photoalignment at both molecular and microscopic level are studied. The holographic performance drastically changes, which can be selectively exploited for either long-term or dynamic holography.

The cell performance of organic-inorganic hybrid photovoltaic devices based on CdSe nanocrystals and the semiconducting polymer poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b′]-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) is strongly dependent on the applied polymer-to-nanocrystal loading ratio and the annealing temperature. It is shown here that higher temperatures for the thermal annealing step have a beneficial impact on the nanocrystal phase by forming extended agglomerates necessary for electron percolation to enhance the short-circuit current. However, there is a concomitant reduction of the open-circuit voltage, which arises from energy-level alterations of the organic and the inorganic component. Based on quantum dots and PCPDTBT, we present an optimized organic–inorganic hybrid system utilizing an annealing temperature of 210 °C, which provides a maximum power conversion efficiency of 2.8%. Further improvement is obtained by blending nanocrystals of two different shapes to compose a favorable n-type network. The blend of spherical quantum dots and elongated nanorods results in a well-interconnected pathway for electrons within the p-type polmer matrix, yielding maximum efficiencies of 3.6% under simulated AM 1.5 illumination.

We investigate hybrid organic/inorganic films using different polymers and CdSe quantum dots (QD) and nanorods (NR) with hexanoic acid (HA)-treated hexadecylamine (HDA) or pyridine as the capping ligands. The volume ratios of the polymer:nanoparticle (NP) blends are studied by spectroscopic ellipsometry and transmission intensity data. Effective medium approximation based on the results of the pristine films is applied. With this routine, the polymer/NP volume ratio of the blend can be identified. In combination with the mass ratio of the components, the mass density of the NP including the inorganic crystalline core and the organic ligand layer is obtained. A geometrical model for QD and NR allows for the estimation of the ligand layer thickness. We find pyridine and HDA after HA treatment to be 0.9 and 0.6 nm on the QD surface, respectively. By contrast, the effective thickness of the organic ligand is 3.0 nm on the investigated NR. In both cases, the organic layer is thicker than a monolayer of the expected pyridine due to the presence of extant synthesis ligands as a result of incomplete ligand exchange. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 000: 000–000, 2011

White organic light-emitting diodes (WOLEDs) offer a range of attractive characteristics and are in several regards conceptually different from most currently used light sources. From an application perspective, their advantages include a high power efficiency that rivals the performance of fluorescent lamps and inorganic LEDs and the potential for a very low cost of manufacturing. As flat-panel light sources they are intrinsically glare-free and generate light over a large area. WOLEDs are constantly improving in terms of performance, durability, and manufacturability, but these improvements require joint research efforts in chemistry and the materials sciences to design better materials as well as in physics and engineering to invent new device concepts and design suitable fabrication schemes, a process that has generated many exciting scientific questions and answers. This article reviews current developments in the field of WOLEDs and puts a special focus on new device concepts and on approaches to reliable and cost-efficient WOLED manufacturing.

This review describes recent advances and applications in the field of organic photorefractive materials, an interesting area in the field of organic electronics and promising candidate for various aspects of photonic applications. We describe the current state of knowledge about the processes involved in the formation of photorefractive gratings in organic materials and focus on the chemical and photo-physical aspects of the material structures employed in low glass-transition temperature amorphous composites and organic photorefractive glasses. State-of-the art materials are highlighted and recent demonstrations of photonic applications relying on the reversible holographic nature of the photorefractive materials are discussed.

In order to be competitive on the energy market, organic solar cells with higher efficiency are needed. To date, polymer solar cells have retained the lead with efficiencies of up to 8%. However, research on small molecule solar cells has been catching up throughout recent years and is showing similar efficiencies, however, only for more sophisticated multilayer device configurations. In this work, a simple, highly efficient, vacuum-processed small molecule solar cell based on merocyanine dyes – traditional colorants that can easily be mass-produced and purified – is presented. In the past, merocyanines have been successfully introduced in solution-processed as well as vacuum-processed devices, demonstrating efficiencies up to 4.9%. Here, further optimization of devices is achieved while keeping the same simple layer stack, ultimately leading to efficiencies beyond the 6% mark. In addition, physical properties such as the charge carrier transport and the cell performance under various light intensities are addressed.

The metastable β-phase morphology, inherent to most polyfluorene homo-polymers, is of interest due to its superior optical and electrical characteristics compared to its amorphous analogue. Here, a polyfluorene with vinyl-ether-functionalized aliphatic side-chains that allow crosslinking is reported. It is demonstrated that the previously induced conformational morphology is preserved in the resulting polyfluorene network, which enables subsequent wet thin-film processing. Electron-beam lithography provides a means for sub-(optical)-wavelength patterning of the crosslinkable polyfluorene films. As a specific demonstration, optically-pumped distributed-feedback (DFB) lasers made from surface-relief gratings in amorphous and β-phase polyfluorene are presented. By backfilling gratings of one morphology by the other, devices are demonstrated that exhibit lasing at two wavelengths with a threshold (<1 μJ cm⁻²) at least an order of magnitude lower compared with previous data.

A series of dipolar donor–acceptor (D–A) chromophores with aminothiophene donor and different heterocyclic acceptor units is reported. By modulation of the acceptor strength, absorption bands over the whole visible spectrum are accessible as well as adjustment of the frontier molecular orbital levels. The performance of the chromophores in blends with fullerene acceptors in solution-processed bulk heterojunction solar cells was studied and related to the molecular properties of the dyes. In particular, the effect of the large ground-state dipole moments of these dyes was investigated by single crystal X-ray analysis, which revealed antiparallel dimers, resulting in an annihilation of the dipole moments. This specific feature of supramolecular organization explains the excellent performance of merocyanine dyes in organic solar cells. With blends of HB366:PC₇₁BM, the most efficient solar cell with a V_OC of 1.0 V, a J_SC of 10.2 mA cm⁻², and a power-conversion efficiency of 4.5 % was achieved under standard AM1.5, 100 mW cm⁻² conditions. Under reduced lighting conditions, even higher efficiencies up to 5.1 % was obtained.

A series of dipolar donor–acceptor (D–A) chromophores with aminothiophene donor and different heterocyclic acceptor units is reported. By modulation of the acceptor strength, absorption bands over the whole visible spectrum are accessible as well as adjustment of the frontier molecular orbital levels. The performance of the chromophores in blends with fullerene acceptors in solution-processed bulk heterojunction solar cells was studied and related to the molecular properties of the dyes. In particular, the effect of the large ground-state dipole moments of these dyes was investigated by single crystal X-ray analysis, which revealed antiparallel dimers, resulting in an annihilation of the dipole moments. This specific feature of supramolecular organization explains the excellent performance of merocyanine dyes in organic solar cells. With blends of HB366:PC₇₁BM, the most efficient solar cell with a V_OC of 1.0 V, a J_SC of 10.2 mA cm⁻², and a power-conversion efficiency of 4.5 % was achieved under standard AM1.5, 100 mW cm⁻² conditions. Under reduced lighting conditions, even higher efficiencies up to 5.1 % was obtained.

The common approach in organic materials science is dominated by the perception that the properties of the bulk materials are virtually determined by the properties of the molecular building blocks. In this Concept Article, we advocate for taking into account supramolecular organization principles for all kinds of organic solid-state materials, irrespective of them being crystalline, liquid crystalline, or amorphous, and discuss a showcase example, that is, the utilization of merocyanine dyes as p-type organic semiconductors in bulk heterojunction (BHJ) solar cells. Despite their extraordinarily large dipole moments, which are considered to be detrimental for efficient charge carrier transport, BHJ organic photovoltaic materials of these dyes with fullerenes have reached remarkable power conversion efficiencies of meanwhile nearly 5 %. These at the first glance contradictory properties are, however, well-understandable on the systems chemistry level.

The efficiency of bulk-heterojunction solar cells is very sensitive to the nanoscale structure of the active layer. In the past, the final morphology in solution-processed devices has been controlled by varying the casting solvent and by curing the layer using heat tempering or solvent soaking. A recipe for making the “best-performing” morphology can be achieved using these steps. This article presents a review of several new techniques that have been developed to control the morphology in polymer/fullerene heterojunction mixtures. The techniques fall into two broad categories. First, the morphology can be controlled by preparing nanoparticle suspensions of one component. The size and shape of the nanoparticles in solution determine the size and shape of the domain in a mixed layer. Second, the morphology can be controlled by adding a secondary solvent or an additive that more strongly affects one component of the mixture during drying. In both cases, the as-cast efficiency of the solar cell is improved with respect to the single-solvent case, which strongly argues that morphology control is an issue that will receive increasing attention in future research.

On p. 240, Klaus Meerholz and co-workers show control over the aggregation of P3HT in solution by mixing a dipolar, but miscible solvent to the coating solution. The resulting nanoparticle dispersions are stable and allow a quantitative comparison of the absorption spectra of amorphous and aggregated P3HT. These results are interesting not only because they allow control of morphology on the nanometer scale, but they also show a path to low-cost morphological control of large-area films, which is an essential step for the commercialization of plastic PV devices.