Ilya V. Golovnin

Dramatic enhancement of photo-oxidation stability of a conjugated polymer in blends with organic acceptor

Photo-oxidation of a prototype conjugated polymer poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) in blended films with 2,4,7-trinitrofluorenone (TNF) is drastically suppressed upon exposure to green laser radiation under ambient conditions that was observed by using Fourier transform infrared spectroscopy. By increasing the TNF concentration in MEH-PPV, we have found that the photo-oxidation rate and the photoluminescence intensity drop together in a correlated way by three orders of magnitude. We suggest that triplet exciton formation in the MEH-PPV/TNF blends is deeply suppressed blocking the photo-oxidation. These findings may open a way to intrinsically photostable conjugated polymer materials for photonic and photoelectric applications.

Acceptor-Enhanced Local Order in Conjugated Polymer Films.

Disorder in conjugated polymers is a general drawback that limits their use in organic electronics. We show that an archetypical conjugated polymer, MEH-PPV, enhances its local structural and electronic order upon addition of an electronic acceptor, trinitrofluorenone (TNF). First, acceptor addition in MEH-PPV results in a highly structured XRD pattern characteristic for semicrystalline conjugated polymers. Second, the surface roughness of the MEH-PPV films increases upon small acceptor addition, implying formation of crystalline nanodomains. Third, the low-frequency Raman features of the polymer are narrowed upon TNF addition and indicate decreased inhomogeneous broadening. Finally, the photoinduced absorption and surface photovoltage spectroscopy data show that photoexcited and dark polymer intragap electronic states assigned to deep defects disappear in the blend. We relate the enhanced order to formation of a charge-transfer complex between MEH-PPV and TNF in the electronic ground state. These findings may be of high importance to control structural properties as they demonstrate an approach to increasing the order of a conjugated polymer by using an acceptor additive.

Novel indolin-2-one-substituted methanofullerenes bearing long n-alkyl chains: synthesis and application in bulk-heterojunction solar cells

Summary An easy, high-yield and atom-economic procedure of a C60 fullerene modification using a reaction of fullerene C60 with N-alkylisatins in the presence of tris(diethylamino)phosphine to form novel long-chain alkylindolinone-substituted methanofullerenes (AIMs) is described. Optical absorption, electrochemical properties and solubility of AIMs were studied. Poly(3-hexylthiophene-2,5-diyl) (P3HT)/AIMs solar cells were fabricated and the effect of the AIM alkyl chain length and the P3HT:AIM ratio on the solar cell performance was studied. The power conversion efficiencies of about 2% were measured in the P3HT/AIM devices with 1:0.4 P3HT:AIM weight ratio for the AIMs with hexadecyl and dodecyl substituents. From the optical and AFM data, we suggested that the AIMs, in contrast to [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), do not disturb the P3HT crystalline domains. Moreover, the more soluble AIMs do not show a better miscibility with the P3HT crystalline phase.

Anomalously high raman scattering cross section for carbon-carbon vibrations in trans-nanopolyacetylene

Absolute Raman scattering cross section on the stretching carbon-carbon vibrational modes of trans-nanopolyacetylene (NPA) was measured at an excitation wavelength of 514 nm. It is shown that the carbon-carbon bonds in trans-NPA scatter light more efficiently than in the diamond structure by several orders of magnitude. The role of resonant Raman scattering and the model of coherent vibrations of carbon-carbon bonds are discussed.

Depolarization degree of diode-pumped single-frequency monolithic ring Nd3+:YAG laser

For the first time depolarization degree of the diode-pumped monolithic ring Nd3+:YAG laser has been measured. The obtained value of depolarization degree equals 3 (DOT) 10-3. It has been shown that the dominant mechanism of the intracavity losses and the output light depolarization is diffraction on random inhomogeneities of birefringence in the laser media.

Frequency sweeping of narrowline diode-pumped microlaser radiation in multipass pulsed slab amplifier

We present results of theoretical and experimental investigations of frequency sweeping mechanisms of the narrowline diode-pumped monolithic ring Nd:YAG laser radiation in multipass pulsed slab amplifier. The obtained value of the maximal chirp in the four-pass slab amplifier does not exceed 7.7 kHz when energy of the pump pulses is 36 J and the duration of these pulses is 0.3 ms.

Stability of excited frequencies in a doubly resonant parametric oscillator

The problem of stability of excited frequencies is considered for a ring doubly-resonant optical parametric oscillator. The theory developed is based on the fixed field approximation used to analyze the interaction of waves on the tip of resonator cavity. It is shown that the excited frequency fluctuations arising due to resonator parameter variations can be largely suppressed. The suppression coefficient of technical fluctuations can be equal to 103 and more.