Bis(1,10-phenanthroline) copper complexes with tailored molecular architecture: from electrochemical features to application as redox mediators in dye-sensitized solar cells

In the last few years, copper coordination compounds turned out to be effective competitors of cobalt complexes as redox mediators in the formulation of iodine-free electrolytes for dye-sensitized solar cells (DSSCs). However, the lack of a clear correlation between electrochemical signatures of copper complexes (i.e. half-wave potential and heterogeneous electron transfer rate) and photoelectrochemical performance of solar devices makes difficult the optimization of their coordination sphere. Therefore, to partially fill this gap and to elucidate the intrinsic correlation between the molecular architecture of these complexes and their electrochemical features, we prepared four Cu+/2+redox couples in which the copper center is coordinated by two 1,10-phenanthrolines bearing various substituents in position 2. These complexes were well characterized, from both electrochemical and spectroscopic point of view, and tested as electron shuttles in lab-scale photoelectrochemical cells sensitized with two efficient \ucf\u80-extended benzothiadiazole dyes. It appeared that 2-aryl-1,10-phenanthrolines effectively combine suitable optical and electrochemical properties. While a fast electron transfer kinetics generally positively affects the dye regeneration process, an optimal balance between dye regeneration efficiency, mass transport and heterogeneous electron transfer at both the counter electrode and at the TiO2interface, must be achieved in order to optimize DSSC performance. Within our series, the top performer was [Cu(2-tolyl-1,10-phenanthroline)2]+/2+which achieved a relative 20% and 15% improvement in power conversion efficiency (under 100 mW s\ue2\u88\u921simulated AM 1.5G illumination) with respect to control cells filled with [Co(bpy)3]2+/3+(bpy = 2,2\ue2\u80\ub2-bipyridine) and I\ue2\u88\u92/I3\ue2\u88\u92electrolytes, respectively

Molecular Tailoring of Phenothiazine Based Hole Transporting Materials for High Performing Perovskite Solar Cells

Phenothiazine based compounds, PTZ1 and PTZ2, were synthesized through straightforward Buchwald Hartwig and Suzuki Miyaura cross couplings, respectively, by binding the suitable donor groups diarylamine or triarylamine to a phenothiazine core. Phenothiazine based structures were proven for the first time as hole transporting materials in solution processed lead trihalide perovskite based solar cells. A dramatic effect exerted by the presence of phenylene spacers was observed on the relevant photovoltaic performances. The power conversion efficiencies measured under AM1.5 sun increase from 2.1 PTZ1 to a remarkable 17.6 PTZ2 , a value rivaling those obtained with the state of the art Spiro OMeTAD 17.7 . These results indicate phenothiazine based compounds as promising candidates to be used as readily available and cost effective hole transporting materials in perovskite solar cell

A convenient synthetic approach to bis-functionalised quaterfluorenes

Ni(COD)2 promoted coupling of bromofluorenes functionalised with boronic esters or trimethylsilyl groups proves to be an efficient method for the prepn. of reactive bifluorenes, which are key intermediates for the synthesis of bis-substituted oligofluorenes. The synthetic method has been exploited as a key step for the synthesis of a chiral 2,7'''-diiodo-quaterfluorene and a 2,7'''-bis-amino quaterfluoren

Heterogeneous optochemical VOC sensing layers selected by esi-mass spectrometry

Spin-coated films of 29H,31H-tetra-4-(2,4-di-tert-amylphenoxy)phthalocyanine (H2Pc) and [P,-S-(dppeS)Pt(CH3)]2[BF4]2 have been used as sensing layers deposited in thin film form for the detection of VOCs. The sensing behaviour of the blend was predicted on the basis of mass spectrometric determinations performed on H2Pc/Pt-complex solutions, by monitoring the formation of gas-phase ions at the electrospray interface. The addition of small amounts of acetonitrile produced a [M+ 41]+ peak whereas the addition of similar amounts of methanol, ethanol and isopropyl alcohol did not give the corresponding [M+ROH]+ species. These results were confirmed by sensing tests. A pure phthalocyanine optosensing element did not show relevant selectivity. Conversely, the heterogeneous sensing layer obtained by spin-coating deposition of a Pt-complex/H2Pc blend allowed the sensing of acetonitrile vapours with respect to the above mentioned alcohols

Rationalizing the Molecular Design of Hole Selective Contacts to Improve Charge Extraction in Perovskite Solar Cells

Two new hole selective materials HSMs based on dangling methylsulfanyl groups connected to the C amp; 8208;9 position of the fluorene core are synthesized and applied in perovskite solar cells. Being structurally similar to a half of Spiro amp; 8208;OMeTAD molecule, these HSMs referred as FS and DFS share similar redox potentials but are endowed with slightly higher hole mobility, due to the planarity and large extension of their structure. Competitive power conversion efficiency up to 18.6 is achieved by using the new HSMs in suitable perovskite solar cells. Time amp; 8208;resolved photoluminescence decay measurements and electrochemical impedance spectroscopy show more efficient charge extraction at the HSM perovskite interface with respect to Spiro amp; 8208;OMeTAD, which is reflected in higher photocurrents exhibited by DFS FS amp; 8208;integrated perovskite solar cells. Density functional theory simulations reveal that the interactions of methylammonium with methylsulfanyl groups in DFS FS strengthen their electrostatic attraction with the perovskite surface, providing an additional path for hole extraction compared to the sole presence of methoxy groups in Spiro amp; 8208;OMeTAD. Importantly, the low amp; 8208;cost synthesis of FS makes it significantly attractive for the future commercialization of perovskite solar cell

Rational Design of Molecular Hole Transporting Materials for Perovskite Solar Cells Direct versus Inverted Device Configurations

Due to a still limited understanding of the reasons making 2,2′,7,7′-tetra­kis­(<i>N</i>,<i>N</i>-di-<i>p</i>-methoxy­phenyl­amine)-9,9′-spiro­bifluo­rene (Spiro-OMeTAD) the state-of-the-art hole-transporting material (HTM) for emerging photovoltaic applications, the molecular tailoring of organic components for perovskite solar cells (PSCs) lacks in solid design criteria. Charge delocalization in radical cationic states can undoubtedly be considered as one of the essential prerequisites for an HTM, but this aspect has been investigated to a relatively minor extent. In marked contrast with the 3-D structure of Spiro-OMe­TAD, truxene-based HTMs <b>Trux1</b> and <b>Trux2</b> have been employed for the first time in PSCs fabricated with a direct (n-i-p) or inverted (p-i-n) architecture, exhibiting a peculiar behavior with respect to the referential HTM. Notwithstanding the efficient hole extraction from the perovskite layer exhibited by <b>Trux1</b> and <b>Trux2</b> in direct configuration devices, their photovoltaic performances were detrimentally affected by their poor hole transport. Conversely, an outstanding improvement of the photovoltaic performances in dopant-free inverted configuration devices compared to Spiro-OMe­TAD was recorded, ascribable to the use of thinner HTM layers. The rationalization of the photovoltaic performances exhibited by different configuration devices discussed in this paper can provide new and unexpected prospects for engineering the interface between the active layer of perovskite-based solar cells and the hole transporters

RANDOM POLY(2,7-FLUORENYLENEVINYLENE) COPOLYMERS OBTAINED BY A SUZUKI-HECK REACTION: SYNTHESIS AND PROPERTIES

The study reports on the synthesis of poly arylene vinylenes by use of a cascade Suzuki-Heck reaction polymerization. The reaction between suitable aryldibromides with potassium vinyltrifluoroborate in the presence of a Pd(0) catalyst permits the access to a series of poly(fluorenylenevinylene)s. The protocol is characterized by a great versatility, deriving from the use of easily attainable substrates, and yields polymers with low percentages of structural 1,1-diarylenevinylene defects. Exploiting this procedure, a series of random poly(9,9-dioctyl-2,7-fluorenylenevinylene-co-N-octyl-3,6-carbazolylenevinylene) copolymers at 20-^80% mol/mol of carbazole (PFV2-6) was achieved. Their properties have been investigated by ^H-NMR, IR, TGA, DSC, cyclic voltammetry, UV-Vis and photoluminescence, and compared to those of poly(9,9-dioctyl-2,7-fluorenylenevinylene) (PFV1) obtained by the same method. The electroluminescence properties of the materials were tested by constructing OLED devices of ITO/PEDOTPSS/ PFV1-6/Ca/AI configuration

Novel bifluorene based conjugated systems: synthesis and properties

A series of novel bifluorene based systems was synthesised by a convergent approach by means of a Suzuki cross-coupling between 7,70-bis-(4,4,5,5-tetramethyl-[1,3,2]dioxaborolan-2-yl)-9,9,90,90-tetraoctyl-2,20-bifluorene and suitable aryl-bromides. All the oligomers have been characterized by 1H, 13C NMR, FT-IR, UV–vis, PL spectroscopy and mass analyses. In particular, it has been demonstrated that the presence of strong electron donor (amines) or withdrawing (carboxylic esters) groups causes a bathochromic shift of the optical properties with respect to those of unsubstituted molecules. The effects of these functional groups on the HOMO–LUMO energy levels were investigated by cyclic voltammetry. Remarkably, the LUMO energy level of 7,70-bis-[50-carbodecaoxy-2,20-bithiophen-5-yl]- 9,9,90,90-tetraoctyl-2,20-bifluorene (K3.07 eV) is strongly influenced by the presence of the ester functional group