In this work, flexible Te films have been synthesized by electrochemical deposition using PEDOT [poly(3,4-ethylenedioxythiophene)] nanofilms as working electrodes. The Te electrodeposition time was varied to find the best thermoelectric properties of the Te/PEDOT double layers. To show the high quality of the Te films grown on PEDOT, the samples were analyzed by Raman spectroscopy, showing the three Raman active modes of Te: E, A, and E. The X-ray diffraction spectra also confirmed the presence of crystalline Te on top of the PEDOT films. The morphology of the Te/PEDOT films was studied using scanning electron microscopy, showing a homogeneous distribution of Te along the film. Also an atomic force microscope was used to analyze the quality of the Te surface. Finally, the electrical conductivity and the Seebeck coefficient of the Te/PEDOT films were measured as a function of the Te deposition time. The films showed an excellent thermoelectric behavior, giving a maximum power factor of about 320 ± 16 μW m K after 2.5 h of Te electrochemical deposition, a value larger than that reported for thin films of Te. Qualitative arguments to explain this behavior are given in the discussion.
New cycloplatinated N-heterocyclic carbene (NHC) compounds with chelate diphosphines (P^P) as ancillary ligands: [Pt(R-C^C*)(P^P)]PF6 (R = H, P^P = dppm 1A, dppe 2A, dppbz 3A; R = CN, P^P = dppm 1B, dppe 2B, dppbz 3B) have been prepared from the corresponding starting material [{Pt(R-C^C*)(µ-Cl)}2] (R = H, A, R = CN, B) and fullycharacterized. The new compound A has been prepared by a stepwise protocol. The photophysical properties of 1A-3A and 1B-3B have been widely studied and supported by the time-dependent-density functional theory (TD-DFT). These compounds show an efficient blue (dppe, dppbz) or cyan (dppm) emission in PMMA films (5%wt), with photoluminescence quantum yield (PLQY) ranging from 30% to 87% under argon atmosphere. This emission has been assigned mainly to transitions from 3 ILCT [π(NHC) → 2 π*(NHC)] excited states with some 3 LL'CT [π(NHC) → π*(P^P)] character. The electroluminescence of these materials in proof-of-concept solution processed OLEDs containing 3A and 3B as dopants was investigated. The CIE coordinates for devices based on 3A (0.22, 0.41) and 3B (0.24, 0.44) fit within the sky blue region. raise the energy of the MC states hindering their photo-or thermal population and then increasing the emission quantum yield and avoiding degradation via bond-breaking processes. 20, 23 The use of didentate cyclometalated carbenes (C^C*) allows to tune the emission properties by changing the nature of both, the C^C* and the ancillary ligands. In this field high efficient blue-emitters have been reported by our group. [19][20][21][22] Those containing chelate diphosphines, such as [Pt (R-C^C*)(P^P)] PF6 (R-C= Naph, R =CO2Et, P^P: dppm (diphenylphosphinomethane), dppe (diphenylphosphinoethane), dppbz (1,2diphenylphosphino-benzene) showed high photoluminescence quantum yields (PLQY) and stability and were proved as the active components in photo-and electroluminescent devices. 21 OLEDs can be manufactured with either vacuum deposition or solution-processing techniques. The former method is suitable for small molecules that, generally, have better performance and longer stability due to the purity of the sublimated samples. [24][25][26] Vacuum deposition, however, requires accurate control on doping concentration and wastes lot of material thereby increasing the manufacturing costs. 27 Recent developments on solutionprocessable OLEDs based on small molecules have focused on optimizing efficiency while using simple processing techniques. 27 However, there are still limited examples, in particular for solution-processable OLEDs based on Pt(II) complexes. 25,26,[28][29][30][31][32][33][34][35][36][37][38][39][40] Within this perspective we decided to extend the family of [Pt(R-C^C*)(P^P)]PF6 compounds by changing the C^C* group. As result, herein we report the synthesis and the structural properties of compounds [Pt (R-C^C*)(P^P)]PF6 (R= H, P^P: dppm 1A, dppe 2A, dppbz 3A; R = CN, P^P: dppm 1B, dppe 2B, dppbz 3B). The photophysical and TD-DFT studies were also carried out, showing photoluminescence...
Fully inorganic cesium lead halide perovskites, such as CsPbI2Br, show enhanced thermal stability compared to hybrid ones, and are being widely investigated as wide bandgap absorbers for tandem applications. Despite their simple stoichiometry, the preparation of highly crystalline and stable cesium lead halides thin-films is not trivial. In general, high efficiency solar cells based on solution-processed CsPbI2Br thin films are prepared with high temperature annealing or with the use of chemical additives. In this work we use solvent-free synthesis to investigate the formation of CsPbI2Br in bulk or in thin-film, via mechanochemical synthesis and multiple-source vacuum deposition, respectively. We demonstrate the importance of fostering halide alloying in the vacuum processing of inorganic lead halide perovskites, which can be attained either by using mixed halide precursors or by increasing the number of precursors (and hence deposition sources). These strategies lead to highly oriented perovskite films even at room temperature, with improved optoelectronics properties. We obtained promising power conversion efficiency of 8.3% for solar cells employing as-deposited perovskites (without any annealing) and of 10.0% for devices based on CsPbI2Br annealed at low temperature (150 °C). This study allowed us to highlight the most promising processes and strategies to further optimize the material deposition as well as the solar cells architecture. 2
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