KEYWORDS: Perovskite, Thin films, Solar cells, Lead, Thin film solar cells, Photovoltaics, Thin film deposition, Multilayers, Atomic force microscopy, Thin film devices
Hybrid organic-inorganic halide perovskites are the most promising materials for photovoltaic applications and especially low-cost, high-efficiency solar cells. Application these promising materials as absorbing thin films inside solar cells caused rapid increase of the power conversion efficiency even above 20% as well as research explosion. Theoretical and experimental investigations are primarily focused on unique electronic properties of these materials result including high carrier mobility, low carrier recombination rates and tunable spectral absorption range. The application field of hybrid perovskites has quickly expanded in terms of the types of materials by substituting one or more of the organic or inorganic ions in one of the most studied perovskites, to obtain the metal halide perovskites AMX3. However, most of the work focused on optimizing the components of solar cells, namely absorbing range of the material and charges collection form the solar cells structure. In contrast, the influence of the technical factors on the device fabrication has been much less explored. This applies especially to techniques for manufacturing multi-layer structures using high vacuum environment, although undoubtedly these techniques allow obtaining the highest quality tin films. This work contains investigation results of the structural properties of the AMX3 perovskites thin films and their influence on the electrical properties multilayer structure of the solar cells. Organic-inorganic AMX3 halide perovskites containing methylammonium lead iodide (CH3NH3PbI3) thin films are used for experimental investigations.
Structural, electronic and optical properties of four organic molecules named L1, L2, L3 and L4 were studied
theoretically using DFT methodology. The UV-vis absorption spectra were investigated also experimentally when the
molecules were dissolved in dicholoromethane. The calculations prove that for chosen molecules better results are
obtained applying the LC-BLYP methodology due to the extended charge distribution and polarity of the molecules. The
molecules L3 and L4 are characterised by the relatively high dipole moment and the low HOMO-LUMO energy gap
splitting. It allows to suppose that these molecules may be useful for the nonlinear optical (NLO) applications. The
solvent effect on the optical properties of the molecules was checked. The calculations were performed using polarisable
continuum model and the data were compared to the experimental results.
Pure deoxyribonucleic acid (DNA) is known to be soluble in water only and exhibits poor temperature stability. In
contrary, it is well known that the complex of DNA – with cetyltrimethyl ammonium (CTMA) is soluble in alcohols and
can be processed into very good optical quality thin films by solution casting and spin deposition.
Despite the success of DNA-CTMA, there is still need for new cationic surfactants which would extend the range of
available solvents for DNA complex. We test and present experimental results of influence of new surfactants based on
benzalkonium chloride (BA), and didecyldimethylammonium chloride (DDCA) for applications in all optical switching.
We present results of studies of the systems containing photochromic molecules, for all-optical switching and amplified
spontaneous emission applications. The systems consisted of: a) deoxyribonucleic acid doped with different
photochromic molecules like Disperse Orange 3 or spiropyranes, and b) photochromic molecules of 4-heptyl-4'-
methoxyazobenzene showing nematic liquid crystalline properties close to the room temperature (above T = 34° C).
Experiments of dynamic birefringence switching were done in Optical Kerr Effect set-up, where for the sample
excitation chopped cw or picosecond pulsed lasers were used. An excellent switching times and reversibility of the
studied processes have been observed. The amplified spontaneous emission in luminescent dye doped biopolymeric
system was achieved under the sample excitation by UV light pulses (355 nm) coming from pulsed Nd:YAG laser.
All optical switching has been studied using the Optical Kerr Effect (OKE) configuration in a biopolymer matrix
containing a photochromic molecule. The biopolymer system consisted of a deoxyribonucleic acid blended with cationic
surfactant molecule cetyltrimethyl-ammonium chloride suitable for optical quality thin film fabrication. The excitation
beams inducing birefringence were delivered from a continuous wave laser at 473 and chopped using a variable
frequency chopper. Additionally auxiliary nanosecond pulses coming from Nd:YAG laser were used. The birefringence
was instantaneously monitored by a weak non-absorbed light from a cw He-Ne laser working at 632.8 nm under crossed
polarizer system. Excellent switching times in the range of microseconds and full reversibility of the studied processes
have been observed.ïýïýïý
We present results of possible applications of a modified DNA-dye system for lasing and dynamic optical information
recording. The system consisted of bio-polymeric matrix made of deoxyribonucleic acid (DNA) substituted with cationic
surfactant molecule cetyltrimethyl-ammonium chloride (CTMA) and doped with a photochromic (Disperse Red 1) or
fluorescent (Rhodamine 6G) molecules.
Results of optical information recording were obtained in a typical degenerate two wave mixing experiment. For sample
excitation we used a linearly polarized light of λ = 514.5 nm delivered by an argon ion (Ar+) laser. For amplified
spontaneous emission measurements we used 6 ns pulses of 532 nm wavelength delivered by Nd:YAG laser doubled in
frequency.
Nonlinear index of refraction n2 of a series of organic solvents was measured by the nonlinear imaging (z-scan) technique. The results were compared with the values derived from the optical third harmonic generation (THG) done at the same (1064.2 nm) wavelength. The systematic differences between the values obtained from the z-scan measurements and from THG are attributed to mainly two factors: rotational contribution to n2 in z-scan measurements, where one measures the light induced birefringence and to the difference in dispersion for n2 derived from Kerr susceptibilities with respect to those derived from THG measurements. The difference is discussed in terms of a three level model for centrosymmetric structures. Applied to silica and benzene the model shows, at the measurements wavelength, a small difference between the two determinations in the case of silica and quite an important one in the case of benzene. A good agreement is observed for silica with the recently determined THG value.
The semi-macroscopic mechanisms responsible for the surface relief gratings (SRG) formation on azobenzene-containing
films are far from deep understanding.1 We present the results of experimental studies of SRG in
PMMA and PVK polymeric matrices. The Monte Carlo (MC) kinetics of polymeric movements is reported for
recently proposed model,2 which mimics the effect of mass transport along the direction of light modulation,
resulting from multiple trans ↔ cis photoisomerisation cycles of functionalized dyes. We show that the model,
symmetric on "microscopic" level, leads to a directed mass transfer from bright to dark places. Preliminary
studies show that the centers of mass of polymer chains undergo a normal diffusion under the light illumination.
No global light-induced ordering of polymeric chains was detected. MC studies were performed for a system
consisting of half a million of model monomers.
Third order nonlinear optical properties (NLO) of thin films of pure DNA-CTMA complex and of those doped with
disperse red 1 (DNA-CTMA-DR1) and copper phthalocyanine (DNA-CTMA-CoPc) chromophores were studied by the
optical third harmonic generation and as function of the dopant concentration. The THG measurements, performed in
vacuum at 1064 nm fundamental wavelength reveal an one orders of magnitude increase of &khgr;(3)(-3&comega;;&comega;,&comega;,&comega;) susceptibility of the DNA-CTMA complex when doped with 5% of DR1. This increase is less important for the complex
doped with CoPc. For both dopants it doesn't follow the chromophore concentration, as it could be expected. This
behavior is interpreted in terms of the influence of local field. The &khgr;(3)(-3&comega;;&comega;,&comega;,&comega;) susceptibility of pure DNA-CTMA
complex is about one order of magnitude larger than for silica plate, used as standard.
The concentration dependence of third order nonlinear optical susceptibility ( χ<3> ) of copper phthalocyanine (CuPc)
dissolved in tetrahydrofuran (THF) using the degenerate four wave mixing (DFWM) method at 532 nm was investigated.
We present the linear dependence of the third order nonlinear optical susceptibility ( χ<3> ) as a function of different
concentration for CuPc dissolved in THF. We also calculated the second order hyperpolarizability (
γ) of CuPc
solutions. Third harmonic generation (THG) measurements at the 1064 nm performed on CuPc thin films are also
presented. We found that the χ<3>DFWM values are larger than the χ<3>THG ones. This variation observed in χ<3> values,
occurs probably due to the different resonance contributions in solution and solid state of CuPc. We show that in the case
of DFWM measurements the one and two-photon resonant contributions at the Q and C-band increase χ<3>DFWM value of
CuPc. In THG measurements, the three-photon resonance contribution at the Soret band gives rise to higher χ<3>THG value.
In this paper the recent results of our studies of linear and nonlinear optical properties of a selected rotaxane are presented and discussed. The studied rotaxane can be processed into good optical quality thin films by vacuum evaporation. The linear optical properties of rotaxane solutions were studied by the UV-VIS spectroscopy and the nonlinear optical properties by the picosecond degenerate four wave mixing and Z-scan methods. The results show important rotational contribution to the nonlinear index of refraction.
The dynamic holography method is applied to determine the response time for trans-cis-trans izomerization process in DR1 chromophore embedded in a solid polymer matrix. The experiments were performed on free standing films using a pulsed ps laser for grating writing and a cw laser for it reading. It is found that the writing process may be well described by a mono-exponential curve with a time constant below ms while the decay process is more complicated and can be approximated by a bi-exponential equation with two response times, significantly larger than for the writing process.
We measure third-order optical response of two organometallic compounds using the degenerate four wave mixing method. From measurements of DFWM efficiency, we deduce the values of third-order susceptibilities χ<3>. From measurements of χ<3>, we deduce the values of the second-order hyperpolarisabilities γ. The merit factor for each compound is given and the value obtained for the most efficient compound in terms of γ(second order hyperpolarizability) is 104 larger than the value of CS2, which is a reference material. The obtained optical nonlinearities are compared to those of other compounds previously studied. A preliminary correlation between structure and third-order optical properties is proposed.
All-optical poling permits the polar orientation of molecules. FOr an efficient poling of thin films, relative phases, amplitudes and polarizations of the two interfering beams must be controlled. We present an original stable one-arm interfermeter which is specific to the recording of two-color interferences. It relies on teh index dispersion of optical glasses. This particular interference technique permits true real-time non-perturbative monitoring of the polar orientation process and a fast all optical poling of thin film materials, without need for phase control.
In the present work we focused our attention on studies of PVK:TNF hybrid polymer liquid crystal panels under short pulse laser illumination conditions. The diffraction gratings in a LC panel were induced by crossed beams generated by doubled in frequency Nd:YAG laser ((lambda) equals 532 nm) delivering pulses of 20 ps duration. So induced gratings were read by a cw laser radiation coming from a weak power He-Ne laser working at (lambda) equals 632.8 nm. The temporal evolution of intensity of first order diffraction measured in PVK:TNF hybrid liquid crystal panels shows many interesting features and complexity dependent on various experimental conditions. The substantial diffraction is observed already in time less than 1 ms after the pulse and the grating decay is completed within hundreds of milliseconds. At least three different steps of grating build-up can be distinguished which depend in various ways on the experimental conditions. A tentative mechanism of the observed responses is discussed in connection with the photoconductive properties of polymeric layers and the optical and electrical properties of the used liquid crystal E-7 (Merck).
All-optical poling technique permits purely optical orientation of dye molecules in a polymer film. The experiment includes two phases: the writing (seeding) period and the readout one. In seeding phase two beams, the fundamental (omega) and its second harmonic (SH, 2(omega) ) irradiate the sample and as a result of the coherent interference between them the second order (chi) (2)-susceptibility grating is encoded, with a period satisfying the phase matching condition for SH generation. During the readout step only the fundamental beam is incident onto the material and the second harmonic beam generated by the medium is observed at the back side of the sample. The coherent superposition of two beams at (omega) and 2(omega) frequencies results in a presence of a polar field E(t) inside the material, which can break the centrosymmetry of the medium. The physical origin of the effect lies in the orientational hole-burning in the initially isotropic distribution of dye molecules. It has been demonstrated that efficient all-optical poling requires optimization of relative intensities and relative phase of the seeding beams. An original technique of non-perturbative monitoring of the all-optical poling process without any necessity of taking care of the phase difference between seeding beams is presented. This new technique was applied to several new dye-polymer systems.
All-optical poling technique permits purely optical orientation of molecules. The experiment consists of two steps: the writing (so-called seeding) period and the readout one. In the seeding phase two beams, the fundamental one ((omega) ) and its second harmonic (SH, 2(omega) ) illuminate the sample and print in the medium the second order (chi) (2) susceptibility grating with a periodicity satisfying the condition of phase matching for SH generation. In the readout period only the fundamental beam irradiates the sample, and the second harmonic generation is observed at the sample output. Efficient all-optical poling requires optimisation of the seeding beam intensities and their relative phase difference. We propose a novel technique for non-perturbative monitoring of the all-optical poling process and the easy method of orienting molecules without any necessity of taking into account the phase difference between seeding beams.
A shape-like modulation of the linear electro-optics (LEO) coefficient versus the pressure (p) and the temperature (T) has been observed for the first time. The modulation depth of the LEO (r222) tensor component in the C60-TTF (for He-Ne laser wavelength λ=633 nm) was equal to about 2.6%. Varying the applied hydrostatic pressure up to 15 GPa and the temperature from 4.2 up to 25K. We have unambiguously demonstrated that the observed effect is caused by incorporation of the TTF moiety and absent in the unsubstituted fullerenes varying the applied hydrostatic pressure up to 19 GPa and the temperature from 4.2 up to 150 K. The data obtained gives a possibility for using the discovered effect for contact-less measurements of low temperatures and high pressures.
The two photon absorption coefficient and third order nonlinear optical susceptibility of ZnSe crystals were investigated using the transmission and degenerate four wave mixing methods. The experimental results show that imaginary part of third order nonlinear optical susceptibility decrease with increase of free carriers and the absolute value of third order nonlinear optical susceptibility increase with increase of free electron concentration.
Despite considerable progress achieved over the past few years in understanding ultrathin oxynitrides, several fundamental questions, in particular the oxynitridation mechanism, and the mechanisms behind the beneficial role of nitrogen, are still not well understood. To better understand the explanations which have been proposed for the phenomena specific to silicon oxynitride and for the nature of the defects, a study of the electron structure of a MOS system using silicon oxynitrides as the gate oxide and based on a first-principle molecular dynamic method, was carried out.
We report large third-order nonlinear optical susceptibilities (chi) <3>ijkl of new tetrathiafulvalene (TTF) derivatives, using the degenerate four wave mixing (DFWM) method. To know the physical origin of their optical nonlinearities, we separate electronic and ionic contributions to nonlinear optical susceptibilities. The electronic contribution to the third-order nonlinear optical susceptibilities of the studied molecules is dominant. From DFWM measurements we also deduce values of the third-order hyperpolarizabilities (chi) which are about 105 greater than the (chi) value for CS2. We have thus shown that the molecules under consideration posses larger third order nonlinear optical susceptibilities compared to the polyazine derivatives, acetylenic analogues of TTF and to the ethylenic TTF derivatives. All theoretical simulations are done within a framework of semi-empirical quantum chemical calculation. A correlation between molecular dipole moments and third order susceptibilities is found.
We report on experimental and theoretical studies of linear electrooptic (Pockels) coefficients in push-pull chromophores incorporating the 1,3-dithiol-2-ylidene moiety as the electron donating. The proposed theoretical approach is based on molecular dynamics geometry optimization and quantum chemical calculations of the appropriate molecules. Intermolecular interactions are taken into account within a framework of solid state local density approximation. The quantum chemical method is based on a self-consistent norm- conserving nonlocal pseudopotential with orthogonalization to the core pseudo-wavefunctions by linear combination of atomic orbitals. Contribution of the electronic and ionic parts into the output electrooptic tensor component r111 ((lambda) equals 633 nm) is evaluated. An enhancement of heteropolar molecular ionicity leads to an increase of the resulting r111 electrooptic coefficient. Vibration (ionic) and electronic modes are found to be sensitive to substitution of the side chemical groups. The dominant role of some particular chemical fragments dominating in the observed coefficients is really evident.
We present a study of Distributed Feedback laser emission in various polymer materials. This laser scheme permits efficient control of the stimulated emission in dye doped polymer materials. Optical feedback is provided by distributed Bragg gratings formed in the film by interference patterns from the pump beam. We demonstrate broad tunability of laser emission in polymeric waveguides doped with stilbenoid, phenylene vinylene and oligomers of phenyl ethynylene used for OLEDs. Laser action was also obtained with Rhodamine 6G in PMMA deposited on surface relief grating and excited in a transverse single beam pumping geometry.
We present a study of Distributed Feedback laser emission in various polymer materials. This permits efficient control of the stimulated emission in dye doped polymer materials. Confinement and waveguiding effects are evidenced. We also propose a dynamical study of the effect using 4 wave mixing in the saturable absorption regime with stimulated emission.
The experimental results of nonlinear optical studies at 532 nm using picosecond pulses of Zn1-xMgxSe films are reported for x equals 7%, 16% and 40%. The effects of doping on linear ((alpha) ) and nonlinear ((beta) ) absorption coefficients are investigated. All studied samples reveal a relatively strong nonlinear absorption which decreases with an increase of Mg content. The undoped sample (0% Mg) displays absorption coefficients almost equal to those of the ZnSe crystal annealed at the same temperature.
Photoinduced optical phenomena in amorphous Sb2Se3- BaCl2-PbCl2 glasses have been studied using experimental spectroscopic and theoretical quantum chemical methods. Photo-induced two-photon absorption (TPA) and second harmonic generation (SHG) were measured for the probing CO2-laser wavelength 10.6 micrometers . CO-laser ((lambda) equals 5.5 micrometers ) was used as a source of photoinducing light. We have found that with an increasing CO-laser exposure the SHG maximum output signal increases and achieves its maximum values at CO photon fluence 18 * 1013 phot./cm2 after the two hours of illumination. The absolute SHG values were not more than one order less comparing with ZnS crystals in case of its third rank nonlinear optical susceptibility tensor components (chi) 222 ((lambda) equals 10.6 micrometers ). With decreasing temperature the SHG signal strongly increases within the 32...26 K temperature range. Time-dependent probe-pump measurements indicate on existence of SHG maximum at time delay about 45 ps. Good correlation between SHG and TPA was observed. Simultaneously spectra positions of TPA maxima are strongly depended on the photoinduced fluence. Contrary to the SHG behavior for the TPA we observe at least two maxima at 26 ps and 70 p.s We explain this dependence within a framework of the quantum chemical approach with taken into account of anharmonic electron-vibrational interaction. Coming out from the performed calculations and IR-spectroscopy Fourier technique measurements in the spectral region between 100 cm-1 and 300 cm-1 we have ascertained a key role of Sb-Se fragments in the observed photoinduced effects. A stage of the reversible photoinduced changes is realized after first cycle of IR photoexposure and thermoannealing. We have compared also the different existing models of the photoinduced changes. The results also show that the observed materials have relatively low non-uniformity through the specimen surfaces and can be used as a powerful tool for investigations of picosecond IR laser processes.
Acousto-optical parameters in the polysilane Sin(CH3)2n + 2 oligomers with the different number of monomers n were investigated as the functions of n and thickness. The maximal value of the acousto-optical quality coefficients was reached at n equals 10 and thickness about 1.25 nm. It was proposed to use the polysilane oligomers as the acousto-optical modulators and deflectors. The influence of the oligomer monomer numbers n on the behavior of the acousto-optical parameters was unambiguously shown. Simultaneously dependence of the acousto-optical coefficients on the thickness of the samples was shown. The data on the acousto-optical quality correlate well with the data obtained by the sound losses in the external electrical fields.
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