Squaraine (SQ) dyes are an important class of electron-donating (donors or p-type) semiconductors for organic solar cells (OSC) due to their facile synthetic access, broad optical absorption with high oscillator strengths, and chemical robustness. Blending them with compatible electron-acceptors (acceptors or n-type) yields OSC devices known as bulk-heterojunction (BHJ) small molecule donor organic solar cells (SMD-OSCs). Through extensive research on materials design, synthesis, characterization, and device optimization over the past ˝ve years, SMD-OSCs employing SQ-based structures have achieved remarkable increases in device power conversion e˚ciency (PCE), now approaching 8%. Although these PCEs have not yet equaled the performance of state- of-the art donor polymers and some other SMD semiconductors, SQ-based OSC progress highlights successful and generalizable strategies for small molecule solar cells that should lead to future advances. In this review, recent developments in SQ-based OSCs are discussed and analyzed.
Two Diketopyrrolopyrrole based latent pigment donor materials were fabricated into thin film bilayer photovoltaic devices featuring PCBM as the acceptor. Thermal deprotection of the thin film, carried out at 200∘ C, returns the dye-like small molecule to the corresponding pristine pigment quantitatively. The connected evolution of electrical and morphological features of pure thin films and blends are examined. A significant decrease in extinction coefficient was noted and correlated both to intrinsic changes of the electronic structure upon cleavage and to an increase in internal scattering due to extensive crystallization. Power conversion efficiencies of 0.33% were achieved for bilayer devices, nearly doubling previous results with latent pigment DPP devices, under comparable experimental conditions.
A persistent limitation of organic semiconductors is their low dielectric constant є r , which limits the performance of bulk heterojunction (BHJ) solar cells. One way to increase є r is to employ high-є r additives, such as PbS nanocrystals (QDs) to BHJ blends. In this work, we use the recombination of the interfacial charge transfer (CT) state as a means to study the effects of PbS nanocrystals on blends of a narrow bandgap copolymer: 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), and phenyl-C61-butyric acid methyl ester (PCBM). We show that at low dilution levels (0.25% - 0.75% by weight), there is a decrease in the relative weight of the CT recombination lifetime (longer decay component); suggesting that there is an increase in the local є r of the ternary blend.
AbstractCo-sensitization is shown to be an effective method to improve the efficiency of dye-sensitized solar cells wherein ruthenium (ii)-based complex sensitizers (N749, N719) is co-sensitized with the metal-free indoline dye (D149), where photovoltaic efficiency of 5.40% is achieved by co-sensitized N749+D149 and efficiency of 4.94% is achieved by co-sensitized N719+D149. The assembled dye-sensitized solar cells were studied by UVvis absorption measurements of dye solutions, the absorption spectra of the dye-sensitized TiO
Synthesis and investigation of optical and thermal properties of a homologous series of highly luminescent nanostructured organosilicon luminophores (NOLs) containing different donor to acceptor ratio (D:A) are reported. Each of the NOL consists of a 1,4-bis(5-phenylthienyl-2-yl)benzene (PTPTP) acceptor unit and four, six or twelve 2,2′-bithienyl donor fragments connected to each other through two or six silicon atoms. These complex molecules show a “molecular antenna” effect with high efficiency of intramolecular energy transfer about 97-98% combined with excellent photoluminescence (PL) quantum yield of 84-91% and fast PL decay time of 0.90-0.95 ns. A significant increase of the molar extinction coefficient from 94 000 to 257 000 M−1cm−1 with increasing the D:A ratio from 4:1 to 12:1 was observed. It was found that increasing the branching extent in the NOLs prohibits their crystallization. Thermal gravimetric analysis (TGA) showed that all the NOLs reported, regardless of their branching extent, are thermally stable up to 455 °C under nitrogen. These characteristics make them promising materials for various organic photonics applications.
The resistive switching effect has been studied in a set of organic polymer - based structures of a different composition and size scale from macro to micro. It is shown that scaling down reduces both the threshold switching voltage Vth and the respective effective electric field Eth. Furthermore, introduction of metal micro particles into a macro scale polymer matrix provides the same effect. Therefore the metal particle incorporation may be regarded as an alternative method of effective scaling, depending on an application. Switching speed of less than 15 ns, threshold voltage Vth ~ (2 – 25) V, 105 cycle endurance, no significant moisture dependence and high retention time 3.5 months for scaled down samples aswell as for metal doped macro samples have been demonstrated. These characteristics are suitable for constructing memory devices. The switching effect mechanisms are discussed.
AbstractTwo new 3,5-dihetarylsubstituted 1,2,4- oxadiazoles 8 a,b, including N-alkyl substituted carbazole and thiophene moieties, were synthesized as potential components of materials for organic electronics devices. Optical and electrochemical properties of all new compounds were investigated. On the basis of the experimental UV absorption data, the values of bandgap energies equal to 3.44 eV (8a) and 3.05 eV (8b) were determined. The values of their ionization potentials, HOMO levels (−5.62 eV for 8a, −5.46 eV – for 8b), as well as their electron affinity levels, LUMO levels (−2.2 eV for 8a, −2.4 eV – for 8b), were calculated from the results of electrochemical studies. The energy of the triplet excited states of 8 a,b was defined with the help of time-dependent density functional theory (TD-DFT), comprising 2.68 eV (8a) and 2.32 eV (8b), where the greatest value of this parameter was for the compound with a shorter conjugation chain.
Traceless transition metal catalysis (Pd, Ni, Cu, etc.) is very difficult to achieve. Metal contamination in the synthesized products is unavoidable and the most important questions are: How to control metal impurities? What amount of metal impurities can be tolerated? What is the influence of metal impurities? In this brief review, the plausible origins of nanoparticle contamination are discussed in the framework of catalytic synthesis of organic electronic materials. Key factors responsible for increasing the probability of contamination are considered from the point of view of catalytic reaction mechanisms. The purity of the catalyst may greatly affect the molecular weight of a polymer, reaction yield, selectivity and several other parameters. Metal contamination in the final polymeric products may induce some changes in the electric conductivity, charge transport properties, photovoltaic performance and other important parameters.
There has been keen interest in group 14 metalloles as building units of conjugated organic functional materials. This short review summarizes our recent work on group 14 metalloles condensed with heteroaromatic systems, including thiophene and pyridine. These condensed metalloles show interesting properties depending on both the group 14 metallole elements and the heteroaromatic systems. High planarity of the condensed systems and interaction between the element σ*-orbital and the heteroaromatic π*-orbital enhance the conjugation in these systems leading to their potential applications as functional materials, such as carrier transporting materials and emissive materials.
Two new D-π-A chromophores composed of an electron-donating carbazole unit linked through π- bridges, bearing 3,4-ethylenedioxythiophene (EDOT) moiety, with an electron withdrawing dicyanovinyl group (DCV) were successfully synthesized involving Suzuki or Heck cross-coupling and Knöevenagel reactions as the key steps. The obtained compounds absorb light over a broad spectral range, including the visible spectrum. The HOMO/LUMO energies and band gap energy values (Eg) were calculated on the basis of the experimental optical and electrochemical data: HOMO, LUMO, Eg (eV), −5.51, −3.14, 2.37 (4), −5.34, −3.14, 2.20 (7). The presence of the HC=CH unit in compound 7 resulted in the increase of the HOMO energy level, the decrease of a band gap value and red shifts of the absorption and emission bands in comparison with those of 4. Large Stokes shifts and broadband luminescence inherent to both chromophores suggest their use as materials for luminescent solar collectors (LSCs). The obtained compounds demonstrated good solubility and suitable thin-film forming properties. For this reason, they may be suitable for solution-processable photovoltaic applications.
In the present paper the synthesis, photoand electroluminescent properties of new rare earth metal complexes prepared and studied at the Razuvaev Institute of Organometallic Chemistry during the last decade are reviewed. The obtained compounds give luminescence in UV, visible and NIR regions. The substituted phenolates, naphtholates, mercaptobenzothiazolate, 8-oxyquinolinolate, polyfluorinated alcoholates and chalcogenophosphinates were used as ligands. The synthesis and structure of unusual three–nuclear sulfidenitride clusters of Nd and Dy are described. The new excitation mechanism of ytterbium phenolates and naphtholates, which includes the stage of reversible reduction of Yb to divalent state and oxidation of the ligands in the excitation process, is discussed.
AbstractIn modern bulk heterojunction (BHJ) organic solar cells, blends of low-bandgap polymer and [70]PCBM acceptor are used in the active layer. In this combination, the polymer absorbs photons from the red and near-IR parts of the solar spectrum, while the blue and near-UV photons are harvested by [70]PCBM. As a result, both electron transfer from polymer to [70]PCBM and hole transfer from [70]PCBM to polymer are of utmost importance in free charge generation and have to be optimized simultaneously. Here we study electron and hole transfer processes in BHJ blends of two low-bandgap polymers, BTT-DPP and PCPDTBT, by ultrafast photoinduced spectroscopy (PIA). By tracking the PIA dynamics, we observed substantially different charge separation pathways in BHJs of the two polymers with [70]PCBM. From the photoinduced anisotropy dynamics, we demonstrated that in the PCPDTBT:[70]PCBM system both electron and hole transfer processes are highly efficient, while in the BTTBPP:[ 70]PCBM electron transfer is blocked due to the unfortunate energy level alignment leaving hole transfer the only pathway to free charge generation. Calculations at the density functional theory level are used to gain more insight into our findings. The presented results highlight the importance of the energy level alignment on the charge separation process.
AbstractPoly(3-hexylthiophene) (P3HT) films and P3HT / fullerene photovoltaic cells have been p-doped with very low levels (< 1 wt. %) of molybdenum tris[1-(trifluoromethylcarbonyl)- 2-(trifluoromethyl)-ethane-1,2-dithiolene]. The dopants are inhomogenously distributed within doped P3HT films, both laterally and as a function of depth, and appear to aggregate in some instances. Doping also results in subtle changes in the local and long range order of the P3HT film. These effects likely contribute to the complexity of the observed evolutions in conductivity, mobility and work function with doping levels. They also negatively affect the open-circuit voltage and fill factor of solar cells in unexpected ways, indicating that dopant aggregation and non-uniform distribution can harm device performance.
The review presents the state-of-the-art analysis of investigations in the field of a new line of research of photochromism – nanophotochromism. The design, properties, and possible applications of photochromic nanoparticles prepared by different methods with the use of photochromic substances (aggregates, host-guest, and polymer systems, solid nanoparticles) aswell as core-shell photochromic nanostructures based on polymers, silica, quantum dots, doped upconversion nanocrystals, and Ag, Au, etc. nanoparticles have been reviewed.
Organic materials for photonics have been a wellestablished field in Russia, and electrophotographic, nonlinear-optical, photorefractive and other photoactive organic materials have been in the focus of Russian researchers for many decades. In this special issue, A.V. Vanninkov et al. review their studies on photoconductive and nonlinear optical properties of polymers doped by metallophthalocyanines. They use Z-scan technique to probe the nonlinear optical properties of the polymer composites and study their photoelectric properties as well. This topic is extended in the paper by Y.N. Luponosov at al., which describes optical, thermal and structural properties of nanostructured organosilicon luminophores (NOLs), based on the donor 2,2′-bithiophene and acceptor 1,4-bis(2,2′-bithiophene-5-yl)benzene units, and their application in organic light emitting diodes (OLEDs). NOL is a branched molecular structure having two types of covalently bonded via silicon atoms organic luminophores with efficient Förster resonance energy transfer (FRET) between them. It was demonstrated that usage of these NOLs as dopants to the electroactive polyfluorene host leads to the efficient spectral downshifting of the electroluminescence and an increase of the OLED performance. A number of papers in this issue review photochromic systems for fabrication of photoswitches interesting for various applications. Photoswitching of magnetic properties is provided by application of spiropyran salts, which alike neutral spiropyrans manifest photochromic transformations in the crystalline state (E.A. Yurieva, S.M. Aldoshin). Results of the synthetic, X-ray and photo-
Full characterization of nanostructured organosilicon luminophores NOL4 and NOL5 based on the donor 2,2’-bithiophene and acceptor 1,4-bis(2,2′- bithiophene-5-yl)benzene units in dilute solutions and thin films by UV-Vis spectroscopy, DSC, TGA and X-ray techniques was reported. It was found that usage of these molecules as dopants (10–20 wt%) to the electroactive polyfluorene host in organic light-emitting devices (OLEDs) leads to the efficient spectral long wavelength shifting of the electroluminescence and an increase of the OLED performance as compared to the devices based on pristine polyfluorene, NOL4 and NOL5.
Organic electronics as a multidisciplinary field requires particularly vast body of expertise in solid-state physics, organic chemistry, physical chemistry and etc. Thus IFSOE had education as its primary focus. Every day the first part lasted until noon and consisted of four hourlong lectures. The core of the IFSOE programme revolves around such topics as organic solar cells, organic transistors, light emitting devices as well as newmaterials for organic electronics. The photophysics was particularly emphasized with a discussion on organic semiconductors and elementary excitations in them, such as excitons, polarons and polaritons, which determine the performance of organic electronic devices. "Most concepts were new tome andmuch of terminology seemed alien at first" says Timur Burganov, a Ph.D student of A.E. Arbuzov Institute of Organic and Physical Chemistry, Kazan Scientific Centre Russian Academy of Sciences. "The first few days were rather hard ones, but then I had quickly adapted and caught on with the rest. Majority of lecturers design their explanations to stem directly from themost basic concepts making it significantly easier to understand. They also highlight latest developments in their respective fields and provide us with useful external references. As a result, not only did I improve the understanding of my initial scientific interest but I also had gathered a certain amount of knowledge of fields relative to mine. Besides, I was strongly impressed with how easy knowledge like that can be practically applied. Organic light emitting diodes, field-effect transistors, solar cells the required prototypes for these devices can be made in a laboratory, which allows us to verify or refute our hypotheses and assumptions independently and in a swift fashion. I look forward to sharing this newlyacquired experience with my local professional community." At the second part of the day, young scientists presented their research during oral and poster sessions. And vast number of the most interesting and the most fertile discussions ultimately took place in the halls of the building and outdoors, also during lunch and dinner, and were informal in their very nature. Furthermore, owing to the sponsorship of Moscow City Government, Russian Foundation for Basic Research, Dynasty Foundation and other organisations the IFSOE had quite versatile and contentrich cultural programme. For those who took part in the school, various activities were organised, including but not limited to: a bustour out-and-around Moscow, a trip to New Jerusalem, a reception with live classical music, soccer matches in the late evenings and an exquisite farewell dinner party. All of these contributed to a relaxed and productive atmosphere which had its strong impact on the audience integrity. The IFSOE had been organised by Sergey Ponomarenko (Enikolopov Institute of Synthetic Polymer Materials) and Dmitry Paraschuk (Lomonosov Moscow State University). "We got this idea about IFSOE exactly a year ago" recalls Sergey Ponomarenko. "The popularity of organic electronics as a field of research spreads rapidly among scientific communities throughout the world. In Russia, a number of laboratories and scientific groups working in this field is growing steadily. Keeping in mind that organic electronics is emerging, the greater part of contributors are quite young. The number of various worldwide scientific conferences and summer schools on organic electronics is just over a dozen, and this led us to realise the necessity of founding one of our own which came to be known as IFSOE. This project includes a world-class scientific conference as well as a school for underand post-graduates and those aspired. To do our best at expanding the horizons and in order to have the opportunity to invite our colleagues from all over theworld to share knowledge and experience we had chosen English as a school language." Today organic electronics gradually flows into commercializaion. The unique features of its devices such
AbstractThe photoconductive, photorefractive and nonlinear optical properties of composites from polyvinylcarbazole or aromatic polyimide containing supramolecular ensembles of (tetra-15-crown-5) - phthalocyaninato gallium, indium, - phthalocyaninateacetato yttrium, - phthalocyaninato ruthenium with axially coordinated pyrazine molecules were investigated at 633, 1030 and 1064nmusing continuous and pulsed lasers. Supramolecular ensembles (SE) were prepared through dissolution of molecular metallophthalocyanines in tetrachloroethane (TCE) and subsequent treatment via three cycles of heating to 90∘C and slow cooling to room temperature. The zscan method in femtosecond and nanosecond regimeswas used for measuring nonlinear optical properties phthalocyaninato indium and yttrium in TCE solutions and polymer films. It was established that effect of heavy metallic atom is basic factor which determines the quantum yield, photorefractive amplification of laser object beam, dielectric susceptibility of third order and nonlinear optical properties of metallophthalocyanines.
In the present review we highlight the main research activities in the field of organic photonics and photovoltaics at the Institute for Problems of Chemical Physics of Russian Academy of Sciences (IPCP RAS). Extensive investigation of optical and electrical properties of π-conjugated organic compounds performed at IPCP RAS since 1960’s resulted in design of many exciting materials representing organic semiconductors, metals and superconductors. Organic Schottky barrier and p/n junction photovoltaic devices constructed at IPCP RAS in 1960’s and 1970’s were among the first examples of reasonably efficient organic solar cells at that time. These early discoveries inspired younger generations of the researchers to continue the work of their mentors and explore the world of organic materials and photonic devices such as molecular photonic switches, organic light emitting diodes, solar cells, photodetectors, photoswitchable organic field-effect transistors and memory elements.
AbstractThree types of bichromophoric styrylquinoline (SQ) dyads are discussed in the review: bisstyrylquinoline dyads, styrylquinoline-merocyanine dyads, and styrylquinoline-naphthol dyads, in comparison with the corresponding model monochromophoric compounds. A variety of photochemical and photophysical processes is observed in the dyads: photoluminescence, reversible and kinetic-driven one-way photoisomerization, [2+2]photocycloaddition with formation of a single rctt-isomer of the cyclobutane derivative, Forster resonance energy transfer (FRET) where the SQ chromophore can act as an energy donor or acceptor. Operation of the dyads as photoswitches and molecular logic gates is also considered.
