Preparation and Characterization of Thin-Film Solar Cells with Ag/C60/MAPbI3/CZTSe/Mo/FTO Multilayered Structures

New solar cells with Ag/C₆₀/MAPbI₃/Cu₂ZnSnSe₄ (CZTSe)/Mo/FTO multilayered structures on glass substrates have been prepared and investigated in this study. The electron-transport layer, active photovoltaic layer, and hole-transport layer were made of C₆₀, CH₃NH₃PbI₃ (MAPbI₃) perovskite, and CZTSe, respectively. The CZTSe hole-transport layers were deposited by magnetic sputtering, with the various thermal annealing temperatures at 300 °C, 400 °C, and 500 °C, and the film thickness was also varied at 50~300 nm The active photovoltaic MAPbI₃ films were prepared using a two-step spin-coating method on the CZTSe hole-transport layers. It has been revealed that the crystalline structure and domain size of the MAPbI₃ perovskite films could be substantially improved. Finally, n-type C₆₀ was vacuum-evaporated to be the electronic transport layer. The 50 nm C₆₀ thin film, in conjunction with 100 nm Ag electrode layer, provided adequate electron current transport in the multilayered structures. The solar cell current density–voltage characteristics were evaluated and compared with the thin-film microstructures. The photo-electronic power-conversion efficiency could be improved to 14.2% when the annealing temperature was 500 °C and the film thickness was 200 nm. The thin-film solar cell characteristics of open-circuit voltage, short-circuit current density, fill factor, series-resistance, and Pmax were found to be 1.07 V, 19.69 mA/cm², 67.39%, 18.5 Ω and 1.42 mW, respectively.     

Some applications of thermal analysis to fullerenes

Thermal analysis is a convenient means of characterizing the soot used as a source of the carbon clusters, the extracted mixture of fullerenes, and the individual clusters themselves. TG in an inert atmosphere will rapidly assay the volatile fractions, presumably the lower molecular weight clusters. TG in oxygen indicates — a slight weight gain for the soots and clusters prior to their combustion.DSC in oxygen is used to determine the heat of combustion for the separated C₆₀ and C₇₀ materials. The combustion occurs around 300°C for the clusters. There is a small exothermic peak before this which is attributed to the oxidation associated with the slight weight gain. The heats of combustion measured are –18.7 and –21.0 kJ·mol^–1 for the C₆₀ and C₇₀ respectively.MS-EGA indicates the loss of small amounts of water and argon at temperatures around 250°C in vacuum and of solvent at about 350°C prior to sublimation.

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Zusammenfassung Thermoanalyse ist ein praktisches Hilfsmittel zur Charakterisierung von Ruß als Quelle für Kohlenstoffcluster, extrahierte Gemische von Fullerenen und die individuellen Cluster an sich. TG in einer inerten Atmosphäre ergibt schnell die flüchtigen Fraktionen, wahrscheinlich die niedermolekularen Cluster. TG in Sauerstoff zeigt einen leichten Gewichtszuwachs für Ruß und Cluster vor ihrer Zersetzung.DSC in Sauerstoff wurde angewendet, um die Verbrennungswärme der getrennten C₆₀ und C₇₀ Materialien zu ermitteln. Die Verbrennung erfolgt für die Cluster bei etwa 300°C. Davor kann ein kleiner exothermer Peak beobachtet werden, welcher der Oxidation in Verbindung mit dem geringen Gewichtszuwachs zugeschrieben wird. Die gemessenen Verbrennungswärmen betragen –18.7 und –21.0 kJ·mol^–1 für C₆₀ bzw. C₇₀.MS-EGA zeigt den Verlust von geringen Mengen an Wasser und Argon bei Temperaturen von etwa 250°C in Vakuum und von Lösungsmittel bei etwa 350°C, bevor die Sublimation eintritt.

     

Spectra of optical phonons and low-energy electronic transitions in C60/TMPD and C60/TPA single crystals

Single Crystals of C₆₀/TMPD and C₆₀/TPA have been grown from a chlorobenzene solution. Optical transmission spectra of single crystals of fullerene complexes withN,N,N,N-tetramethyl-p-phenylenediamine (TMPD) and triphenylamine (TPA) are studied in the spectral range from 600 to 16000 cm^–1. Splitting of the intramolecular vibration of C₆₀ is observed at 1428 cm^–1, which is likely caused by freezing of the rotation of the C₆₀ molecules due to their interaction with amines. Single crystals of C₆₀/TMPD differ from those of C₆₀/TPA by a decrease in the vibration frequency at 1428 cm^–1, vibrations of the C-C bonds of the TMPD molecule, and the redistribution of the forces of the oscillators of the vibrations of the C-N bonds. These peculiarities are interpreted to be the result of partial electron transfer from TMPD to C₆₀ in the C₆₀/TMPD single crystals. The electron transfer in the C₆₀/TPA system is less pronounced.Translated fromIzvestiya akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1459–1464, June, 1996     

Selective reduction of fullerene C60 by metals in neutral and alkaline media. Interaction of C60 with KOH

The reduction of fullerene C₆₀ by Zn and Mg in DMF was studied both in the presence and absence of KOH. Fullerene C₆₀ was reduced in these systems to form the C₆₀ ^n– (n = 1, 2, and 3) anions. The anions were detected by optical and ESR spectroscopies. It was found that Mg reduced C₆₀ to the monoanion, Mg/KOH and Zn reduced C₆₀ to the dianion, and Zn/KOH reduced C₆₀ to the trianion. Like KCN, potassium hydroxide adds to fullerene upon interaction with C₆₀ in DMF. The reaction of C₆₀ with KOH in benzonitrile was accompanied by the generation of the fullerene monoanion. A possible mechanism of the formation of fullerene monoanions in the presence of KOH is discussed. The degradation of the C₆₀ ^n– anions in air was studied.     

Quenching excited triplet C60 fullerene by tetracyanoethylene in benzonitrile

Quenching excited triplet³C₆₀ fullerene by tetracyanoethylene (TCNE) in a benzonitrile solution proceeds with a rate constant equal to (4.2±0.3) · 10¹⁸ (M · s)^–1. The formation of a radical ion pair [C₆₀ ⁺ · · · TCNE^–] was observed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1228–1230, July, 1993.     

Sol-Gel Preparation of Fast Proton-Conducting P2O5-SiO2 Glasses

We have investigated the proton conductivities of the sol-gel-derived P₂O₅-SiO₂ glass at –50 to 120°C. The obtained glass is porous, where the surface area, pore volume and pore diameter are 740 m²/g, 0.5 cm³/g and <5 nm, respectively. The freezing temperature of water molecules adsorbed in the pores was –20°C, which is much lower than that of free liquid water due to the quantum size effect of the water confined in the pores. The electrical conductivities followed the Arrhenius equation in the temperatures between –20 and 120°C. Below –20°C, the adsorbed-water molecules were frozen, resulting in a rapid decrease of the proton conductivity. Considering the high conductivity, chemical and thermal stability, this oxide glass membranes have potential for the fuel cell membrane.     

Preparation of Titanium Oxide Layer on Silica Glass Substrate with Titanium Naphthenate Precursor

Nanocrystalline TiO₂ thin films on silica glass substrates were prepared by using a naphthenic acid precursor. As-deposited thin films were heat treated at 500, 600, 700 and 800^∘C for 30 min in air. The TiO₂ thin films were analyzed by High Resolution X-ray diffraction, ultra violet—visible—near infrared spectrophotometer, field emission—scanning electron microscope and scanning probe microscope. After annealing at 600 and 700^∘C, the XRD patterns consist of only anatase peaks of TiO₂ film. Rutile(110) peak begins to appear at an annealing temperature of 800^∘C. Relative high transmittance at visible range was obtained for all films except the film annealed at 800^∘C. Optical band gap, E_g, is in the range between 3.53 and 3.78 eV except the TiO₂ film annealed at 500^∘C. The best hydrophilicity was achieved with a high-temperature annealing.     

Reactions of excited fullerenes C60 and C70 studied by mass spectrometry

The transformation of the mass spectra of the laser-desorbed C₆₀ and C₇₀ samples with a successive increase in the laser power, resulting in an increase in the degree of excitation of C₆₀ (C₇₀) and in the number of the particles in the laser plume, was studied. Unusual metastable clusters (C₆₀ + C₂) and (C₇₀ + C₂) are formed even at a minimum laser power and begin to dissociate after 0.5 s following a short (3 ns) laser pulse. An increase in the laser power results in the appearance of peaks of metastable clusters C₆₂ (C₇₂) with the statistically normal lifetime without a delay of dissociation. A further increase in the laser power produces metastable clusters C_60k–2n and C_70k–2n (k = 2, 3) formed without a lag from the dimers and trimers of C₆₀ (C₇₀) by the ejection of a number of C₂ required for the stabilization of the C₂ molecules. The peak of C₇₀ appears simultaneously with the appearance of the (C₆₀)_2–2n peaks upon the laser desorption of pure C₆₀. These findings provide evidence for the growth of the excited fullerene clusters by coalescence and subsequent stabilization due to the ejection of a small fragment rather than by the implantation of C₂ into the fullerene framework. This mechanism of cluster growth should be taken into consideration in modeling fullerene formation in an electric arc reactor, because the clusters formed under these conditions have a substantial excess internal energy.     

Application of Alumina Aerogels as Catalysts

Al₂O₃ gels prepared by hydrolysis of Al-alkoxide were applied as catalysts for NO reduction by hydrocarbon. Xerogels were obtained by drying at 90°C, for 24 h, in air. Aerogels were prepared by supercritical drying of the wet gels in ethanol, using an autoclave. The catalyst activity of the gels for NO reduction with C₃H₆ as determined at 200–600°C in a fixed bed flow reactor. NO conversion to N₂ was about 60% at 550°C with both catalysts, and at 600°C it was better with the aerogel than with the xerogel. The specific surface area of the xerogel, which was larger than that of the aerogel as-dried, decreased to 1/3 by annealing at >500°C. However, the surface area of the aerogel hardly changed by annealing at temperatures up to 700°C. The bimodal pore size distribution of the aerogel hardly changed by annealing, too. The microstructure of the aerogels is stable at high temperatures, and they are better catalysts at high temperatures.     

Reduction of C60 and C70 by primary amines: Optical and ESR studies

Radical anions C70- and C70 2- were obtained in vacuo by the reaction of I-amino3-propanol (AP) and 1,5-diaminopentane (DAP) with fullerene C70. The radical anions were identified by visible/near IR (X = I372 and I172 nm, respectively) and ESR spectroscopies. The temperature dependences of the ESR spectra were studied for the C₆₀-AP, C₇₀-AP, and C70-DAP systems. At low temperatures (I5-45 K), the ESR spectrum for C60 is close to that for species with axial symmetry of theg-factor (q_| = 2.000 and g, = I.995). The anisotropy of theg-factor is averaged, when the temperature increases. At T > I48 K the averaged line is broadened, and the sharp signal with g = 2.0001 overlaps this broad line. The intensity of the narrow line increases, when the temperature increases. The ESR spectrum observed in the C₇₀-AP system at I2.5 K may be tentatively described as a superposition of two ESR spectra, namely, the ESR spectra of a radical with g_| = 2.0042 and g, = 2.0015 (presumably a radical cation) and of C₇₀ ^– with q_| = 2.000 and g = I.994. The spectra of the sample in which C70 is present mainly as C₇₀ ^2– exhibit only a line with g = 2.0004.Translated from Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. I, pp. 103–108, January, 1996.     

A complex of buckminsterfullerene with sulfur,C60·2S8: synthesis and crystal structure

The C₆₀·2S₈ complex was prepared by reaction of buckminsterfullerene C₆₀ with sulfur in trichloroethylene and its single-crystal X-ray structure was studied at room temperature. Crystals of this compound are monoclinic, space groupC 2/c, a=20.90(1),b=21.10(1),c=10.537(9) Å, =111.29(7)°,Z=4,d _calc=1.89 g·cm^–3. The crystal structure of the C₆₀·2S₈ complex consists of packed fullerene molecules that form hexagonal channels along thec axis with eight-membered crown-shaped S₈ cyclic molecules inside the channels. The distances between the centers of neighboring fullerene molecules are 10.036(7), 10.636(7), and 10.537(9) Å. Each C₆₀ molecule is linked to eight S₈ molecules with ten shortened intermolecular contacts C...S 3.41(1)–3.52(2) Å. The average values of the C=C and C-C bond lengths are 1.32(3) and 1.47(3) Å, which attest to a significant degree of localization of electron density in the c₆₀ molecule.Translated from Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 262–266, February, 1994.     

Laser flash photolysis of fullerols of C60 and of C70 in aqueous solutions

Fullerols of C₆₀ and of C₇₀ [C₆₀(OH)_n, C₇₀(OH)_m], water-soluble fullerene derivatives, unlike some other fullerene derivatives (such as C₆₀ (C₄H₆O), C₆₀ (C₃H₇N) and C₆₀ [C(COOEt)₂]_x), do not result in excited triplet state but in ionization via monophotonic process in aqueous solutions with 248 nm laser. The quantum yields of formation of hydrated electron (Φ_e ⁻) are determined to be 0.08 and 0.11 for fullerols of C₆₀ and of C₇₀ respectively at room temperature (ca. 15°C) with KI solution used as reference. By laser flash photolysis and oxidation of sulfate radical anion SO₄ ⁻, the fullerol radical cation or neutral radical of C₆₀ is confirmed to be existent and the transient absorption spectra of fullerol radical cation of C₇₀ are observed for the first time. Project supported by the National Natural Science Foundation of China     

Recrystallization-induced defect porous nature of C60 crystals

Defective state of C₆₀ crystals was controlled by the recrystallization and annealing. The defective structure was examined by the X-ray diffraction and N₂ adsorption at 77 K. Recrystallized C₆₀ crystals without annealing showed broad diffraction peaks and the N₂ adsorption isotherm had marked low pressure uptake and a hysteresis in the high pressure region, indicating presence of both micropores and mesopores. The average micropore width was 8 Å which is closed to the C₆₀ molecular size, while the average mesopore one was 50 Å. The mesopores disappeared by annealing up to 393 K. On the other hand micropores of 8 Å remained even by heating up to 673 K.     

Crystal solvate of C60 with tricloroethylene,C60 · C2HCl3

Extraction of fullerenes from carbon soot by trichloroethylene has been studied. We have found that C₆₀ forms a solvate with trichloroethylene (C₆₀ · C₂HCl₃:a=31.31(1);b= 10.156(4);c=10.146(4) Å;V=3228.6 ų,Z=4,d _calc=1.752 g cm^–3, orthorhombic symmetry). Its thermal stability has been studied using TG and DSC. A phase transition of the first order at 167 K has been detected.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1248–1250, July, 1994.The authors are grateful to V. P. Bubnov and I. S. Krainskii for providing them with the samples of fulle-rene-containing carbon soot, and to M. G. Kaplunov and A. V. Zvarykina for assistance in the work.This work was carried out with the financial support of the Russian Foundation for Basic Research, Project Nos. 93-03-18705 and 93-03-5650.     

Stability studies of an electrochemically formed [C60]fullerene-palladium two-component film

The stability of C₆₀ and palladium two-component films, C₆₀/Pd, has been investigated. The effect of different polymerization conditions on the electrochemical stability of the film upon prolonged potential cycling has been studied. Stable voltammetric behavior was observed for polymers formed at potentials less negative than the potential of third C₆₀ reduction step. The incorporation of palladium particles into the structure of C₆₀/Pd polymers increases the polymer stability. The C₆₀/Pd films are doped with supporting electrolyte cations during reduction. The size of these cations is a crucial factor in determining the stability of the film. A strong solvent effect on the potential stability of the film was also observed. The wildest range of stable voltammetric properties was found for acetonitrile and N,N-dimethylformamide. No effect of the temperature on the film stability was observed. The results reported in this work allow for the determination of the optimal conditions for the formation of stable C₆₀/Pd films.     

The reaction of ethyl 2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate with fullerene C60

Heating (100 °C, toluene) or photolysis (Nd³⁺ : YAG laser, = 532 mil, benzonitrile) of a mixture of ethyl 2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate (Hantsch ester) (1) and fullerene C₆₀ under anaerobic conditions results in the formation of fullerene hydrogenation products and ethyl 2,6-dimethylpyridine-3,5-dicarboxylate, which is the product of dehydrogenation of1, identified by IR spectroscopy and mass spectrometry. The triplet state of C₆₀ is quenched by the Hantsch ester.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2531–2534, October, 1996.     

Optical response of cesium coated C60

Photoabsorption spectra are reported for Cs _n ⁺ and C₆₀Cs_n ⁺ + clusters for n=40, 60, 120 and 310. The spectra were obtained by heating the mass selected clusters in a beam by means of photoabsorption until they evaporated metal atoms. The resulting mass loss was observed in a time-of-flight mass spectometer. The plasmon-like resonance in pure Cs clusters shifts to lower energies with decreasing cluster size. The collective electronic excitations in clusters containing C₆₀ are split in energy as would be expected for fullerene molecules coated with layers of metal.     

Thermal Stability of C60-Methylnaphthalenes Solvates

The crystalline solvates containing fullerenes and (di)methylnaphthalenes were investigated by thermal analyses and X-ray diffraction methods. It was found that C₆₀ with (di)methylnaphthalenes forms two types of stable solvates: either at the molar ratio 1:2 decomposing at temperatures close to 100°C or at 1:1 molar ratio decomposing in the temperature range 120–214°C. Crystalline lattice and thermal stability of the solvates depends on the structure of the solvent molecules. The strong solute-solvent interaction is also manifested by the modification of the C₆₀ absorption spectra in solution. The results are discussed using semiempirical quantum chemistry methods. This revised version was published online in August 2006 with corrections to the Cover Date.     

ESR study of spin-adducts of trimethylaminoboryl radicals with fullerene C60

It was established by ESR that trimethylaminoboryl radicals formed by UV irradiation of BH₃NMe_6w in the presence of di-tert-butyl peroxide in saturated benzene solutions of fullerene C₆₀, add to fullerenes to give C₆₀-BH₂NMe₃ spin-adducts. The latter undergo dimerization with a rate constant ofca. 2.5 · 10⁶ L mol^–1 s^–1. A more prolonged photolysis of excess BH₃NMe₃ in a benzene solution of C₆₀ results in multiple addition of the trimethylaminoboryl radicals to the fullerene to give stable radicals C₆₀[BH₂NMe₃]_n.Translated fromIzyestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 673–675, April, 1994.     

The weak interaction between C60 and molecular iodine in solution

Fullerene C₆₀ forms a weak molecular complex with iodine. Its stability constant is much less (–1 mol^–1 than that determined in another study.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 2129—2130, August, 1996.