A low-temperature solution process technique is employed to develop an inorganic cesium carbonate (Cs2CO3) as an electron transport material for inorganic–organic hybrid double cation (FAPbI3)0.85(MAPbBr3)0.15 perovskite solar cells, as an alternative to the conventional thick and meso-TiO2. A device structure of compact-TiO2/Cs2CO3 (0.2 wt. %)/perovskite/spiro-OMETAD leads to enhanced performance of the photovoltaic device, achieving a short-circuit current density (Jsc) of 22.26 mA/cm2, an open-circuit voltage (Voc) of 1054 mV, a fill factor (FF) of 71.6%, and a power conversion efficiency (PCE) of about 17% under one sun illumination, whereas the controlled device structure shows an efficiency of 16.58% without such surface modification layer. Additionally, a device structure of Cs2CO3 (6 wt. %)/perovskite/spiro-OMETAD without any TiO2 ETM has shown a Jsc of 15.40 mA/cm2, Voc of 1023 mV, FF of 51.7%, and a PCE of 8.14%. On the other hand, external quantum efficiency (EQE) data yields around 85% of incident photon to electron conversion for c-TiO2/Cs2CO3 (0.2 wt. %)/perovskite/spiro-OMETAD structure and integrated Jsc extracted from EQE data confirms that Jsc obtained from the current–voltage test is within a close agreement. The obtained results indicate that there is a possibility to further increase the performance of perovskite-based cells and reduce their processing cost by replacing the thick mesoporous TiO2 by Cs2CO3.
A new, but archetype compound [Ir(ppy-F2)2Me4phen]PF6, where ppy-F2 is 2-(2',4'-
fluorophenyl)pyridine and Me4phen is 3,4,7,8-tetramethyl-1,10-phenanthroline, was synthesized and used
to prepare a solid-state light-emitting electrochemical cell (LEC). This complex emits blue light with a
maximum at 476 nm when photoexcited in a thin film, with a photoluminescence quantum yield of 52 %.
It yields an efficient single-component solid-state electroluminescence device with a current efficiency
reaching 5.5 cd/A and a maximum power efficiency of 5.8 Lm/Watt. However, the electroluminiscence
spectrum is shifted with respect to the photoluminiscence spectrum by 80 nm resulting in the emission of
green light. We demonstrate that this unexpected shift in emission spectrum is not originating from the
way of excitation, nor from the presence of large concentrations of ions, but is related to the concentration
of the ionic transition metal complex in the thin film. The origin of the concentration dependent emission
is extensively commented and argued to be related to the population of either 3LC π-π* or 3MLCT triplet
states, in diluted and concentrated films, respectively. Using quantum chemical calculations we
demonstrate that three low-energy triplet states are present with only 0.1 eV difference in energy and that
their associated emission wavelengths differ by as much as 60 nm from each other.
KEYWORDS: Absorption, Ruthenium, Dye sensitized solar cells, Photovoltaics, Solar energy, Solar cells, Nanoparticles, Quantum efficiency, Energy efficiency, Titanium dioxide
A new ruthenium sensitizer based on a heteroaromatic-4,4'-π-conjugated 2,2'-bipyridine, bearing conjugated π-excessive
heteroaromatic rings as donors is presented. Dye-sensitized solar cells have been fabricated based on the novel ruthenium
complex [Ru(II)LL'(NCS)2] (L = 4,4'-bis[(E)-2-(3,4-ethylenedioxythien-2-yl)vinyl]-2,2'-bipyridine, L' = 4,4'-
(dicarboxylic acid)-2,2'-bipyridine) and their photoelectrochemical properties have been measured under various
conditions. Using this sensitizer photovoltaic efficiencies up to 9.1 % under standard global AM 1.5 sunlight were
obtained. DFT/TDDFT calculations have been performed for the sensitizer in solution. By calculating the excited states
energy and character and comparing the results with the conduction band edge of a model TiO2 nanoparticle, we were
able to highlight the factors affecting the measured photovoltaic efficiencies.
The effect of electronic and nuclear factors on the dynamics of dye-to-semiconductor electron transfer was studied employing RuII(terpy)(NCS)3 sensitizers grafted onto transparent films made of titanium dioxide nanoparticles. Various approaches were strived to understand the dependence of the kinetics of charge injection and recombination processes upon the distance separating the dye molecules and the redox active surface. A series of bridged sensitizers containing p-phenylene spacers of various lengths and phosphonic anchoring groups were adsorbed onto TiO2 films. The kinetics of interfacial charge transfer was recorded by use of time-resolved spectroscopy in the fs-ps domain. The electron injection process was found to be biphasic with a clear exponential distance dependence of the fast kinetic component. The slower part of the kinetics was essentially unaffected by the length of the spacer bridge and was attributed to sensitizer molecules that are weakly bound to the surface with no direct contact of the anchoring group with the semiconductor. In a second approach, the kinetics of both forward- and back-electron transfer across a layer of insulating Al2O3 deposited onto TiO2 nanocrystalline particles was investigated. Efficient charge injection was observed over distances up to 3 nm.
The further morphological investigation of nanocrystalline TiO2 films, which sensitized by suitable transition metal complexes forming a new type of molecular photovoltaic systems, the studies of new films and a new Co complexes are presented herein. Scanning electron microscopy, X-ray single crystal and powder diffraction as well as X-ray diffraction at low glancing angles using synchrotron radiation have been used. The morphology of electro- and thermodeposited Pt-layers on TCO (a), polymorphic composition of films (b), possible geometry of location of complex dye molecules on the exposed most faces of TiO2 microcrystals (c) and the crystal structure of a Co(II) complex solvated by electrolyte 4- methyl-1,3-dioxolan-2-on as a precursor of the corresponding redox-system (d) are discussed.
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