A Silanol-Functionalized Polyoxometalate with Excellent Electron Transfer Mediating Behavior to ZnO and TiO 2 Cathode Interlayers for Highly Efficient and Extremely Stable Polymer Solar Cells

Combining high efficiency and long lifetime under ambient conditions still poses a major challenge towards commercialization of polymer solar cells. Here we report a facile strategy that can simultaneously enhance the efficiency and temporal stability of inverted photovoltaic architectures. Inclusion of a silanol-functionalized organic–inorganic hybrid polyoxometalate derived from a PW9O34 lacunary phosphotungstate anion, namely (nBu4N)3[PW9O34(tBuSiOH)3], significantly increases the effectiveness of the electron collecting interface, which consists of a metal oxide such as titanium dioxide or zinc oxide, and leads to a high efficiency of 6.51% for single-junction structures based on poly(3-hexylthiophene):indene-C60 bisadduct (P3HT:IC60BA) blends. The above favourable outcome stems from a large decrease in the work function, an effective surface passivation and a decrease in the surface energy of metal oxides which synergistically result in the outstanding electron transfer mediating capability of the functionalized polyoxometalate. In addition, the insertion of a silanol-functionalized polyoxometalate layer significantly enhances the ambient stability of unencapsulated devices which retain nearly 90% of their original efficiencies (T90) after 1000 hours

Fotofyzikální a protonační time-resolved studie donor-akceptorového rozvětveného systému s pyridinovými akceptory

A comparative study of the photophysical properties of octupolar pyridyl-terminated triphenylamine molecule, with its quadrupolar and dipolar analogues, by means of ambient and low temperature steady state spectroscopy and femtosecond to nanosecond time-resolved fluorescence spectroscopy is reported. The push-pull molecules bear triphenylamine electron donating core, pyridine peripheral electron acceptors, and acetylene pi-bridge. The samples were studied in solvents of varying polarity and also upon addition of small amounts of acetic acid to induce protonation of the pyridine group. All samples exhibit significant positive fluorescence solvatochromism as well as a relaxation of their excited state to a solvent relaxed intramolecular charge transfer state on the picosecond time scale. For the octupolar compound, excited state relaxation occurs simultaneously with excitation energy hopping among the branches. The hopping time is solvent polarity controlled since it becomes slower as the polarity increases. The experimental hopping times are compared to those predicted by Forster and Fermi formulations. The samples are capable of emitting broadband light covering almost the whole visible spectrum by careful control of protonation. Energy transfer from the neutral toward the protonated species on the 1 ps time scale is revealed.Porovnávací studie fotofyzikálních vlastností oktupolárních pyridin-trifenylaminů s jejich kvadrupolárními a dipodálními analogy pomocí steady-state spektroskopie a femtosekundové až nanosekundové time-resolved fluorescenční spektroskopie při běžné a nízké teplotě. Látky byly studovány v rozpouštědlech s různou polaritou, byl studován také vliv přídavků kyseliny octové vedoucí k protonaci pyridinových skupin. Díky kontrolované protonaci vzorky vykazovaly širokopásovou emisi pokrývající téměř celé viditelné spektrum

Photophysics, electronic structure and solar cell performance of a donor-acceptor poly(N-dodecyl-2,7-carbazole-alt-benzothiadiazole) copolymer

In this contribution, we investigate the optoelectronic properties of a donor-acceptor poly(N-Dodecyl-2,7-carbazole-alt-benzothiadiazole (CBZ-BT) copolymer in solutions and thin films, by a combination of complementary optical and electronic spectroscopy techniques including stationary absorption and fluorescence, femtosecond time-resolved and ultraviolet/x-ray photoelectron spectroscopy. Absorption spectroscopy revealed two bands at 322/338 and 445/475 nm for CBZ-BT in solutions/films attributed to the carbazole and benzothiadiazole groups respectively. Photoexcitation either to the absorption band of the carbazole or benzothiadiazole group led to a broad and structureless fluorescence spectrum due to large torsional disorder in the excited state, originating from intramolecular energy transfer between carbazole and benzothiadiazole. Time resolved spectroscopy in solutions reveals a transient red-shift of the emission spectrum within less than 5 ps due to exciton migration and/or conformational relaxation of the polymer backbone. In films, this relaxation is faster accompanied by a quenching of the exciton lifetime

Dynamics of Intramolecular Energy Hopping in Multi-Bodipy Self-Assembled Metallocyclic Species: A Tool for Probing Subtle Structural Distortions in Solution

The intramolecular excitation energy transfer (EET) processes in a series of fluorescent-unquenched, self-assembled metallocycles consisting of spatially fixed-separated and parallel-aligned Bodipy chromophores, are investigated here by steady-state and femtosecond-fluorescence upconversion measurements in the solution phase. These multi-Bodipy macrocycles, namely, the rhomboid (<b>A1</b>), the tetragon (<b>A2</b>) and the hexagon (<b>A3</b>), are formed via temperature-regulated Pt­(II)–pyridyl coordination and consist, respectively, of two, four, and six Bodipy subunits, which are locked at the corners and aligned with their long molecular axes perpendicular to the rigid polygonal frame formed by the alternating B···Pt­(II) connectivities. Extensive simulations and fits to the experimental fluorescence anisotropy decays <i>r</i>(<i>t</i>) show that EET within the cyclic scaffolds is quite <i>uniform</i> and much <i>faster</i> than the intrinsic decay rate of the Bodipy’s. The equalization of the excitation survival probabilities over time of all chromophores is found to be dependent upon the size of the macrocycle. From the observed dynamics supported by geometry optimization calculations, it is concluded that, in contrast to the model compound <b>A1</b>, in the large macrocycles the perfect parallel orientation of the Bodipy dipoles is lifted through limited out-of-plane distortions of the metallocyclic framework from a planar conformation. Additionally, we show that, as opposed to analogous covalent macrocycles, the survival probability of excitons as well as the degree of symmetry distortion and homogeneity in dipole spacing remains nearly intact as the size of the macrocycle increases from tetragon to hexagon

Plasma induced degradation and surface electronic structure modification of Poly(3-hexylthiophene) films

Plasma treatment is an environmentally friendly solution for modifying or nanostructuring the surface of several materials including photoactive polymers. The detailed characterization of the effect of plasma treatment on chemical and optoelectronic properties of photoactive polymers is, therefore, of specific interest. Herein, the effect of the exposure of poly(3-hexylthiophene) (P3HT) thin films to plasma created in three different gases (oxygen, argon and hydrogen) was studied. A range of spectroscopic techniques, such as x-ray (XPS) and ultraviolet (UPS) photoelectron spectroscopy in conjunction with UV–vis absorption, Fourier transform infrared (FTIR) and photoluminescence (PL) spectroscopies, are employed to quantify the extent of chemical modification occurring in each particular case. It is shown that oxygen plasma treatment leads to the disruption of the π-conjugation via the direct oxidation of the sulfur atom of the thiophene ring while the aliphatic side chain remains nearly unaffected. An oxidation mechanism is proposed according to which the sulfur atom of the thiophene ring is oxidized into sulfoxides and sulfones, which subsequently degraded into sulfonates or sulfonic acids in a relatively small degree. For argon and hydrogen plasma treatments some oxidation products are detected only at the polymer surface. In all cases the polymer surface Fermi level is shifted closer to the highest occupied molecular orbital (HOMO) energy after plasma treatment indicating p-type doping arising from surface oxidation.</p

Low Work Function Lacunary Polyoxometalates as Electron Transport Interlayers for Inverted Polymer Solar Cells of Improved Efficiency and Stability

From Crossref via Jisc Publications RouterHistory: epub 2017-06-28, issued 2017-06-28, ppub 2017-07-12Funder: General Secretariat for Research and Technology; FundRef: 10.13039/501100003448Funder: European Regional Development Fund; FundRef: 10.13039/501100008530Funder: European Social Fund; FundRef: 10.13039/50110000489