Stability of MAPbI3 perovskite grown on planar and mesoporous electron-selective contact by inverse temperature crystallization.

Single crystalline perovskite solar cells (PSC) are promising for their inherent stability due to the absence of grain boundaries. While the development of single crystals of perovskite with enhanced optoelectronic properties is known, studies on the growth, device performance and understanding of the intrinsic stability of single crystalline perovskite thin film solar cell devices fabricated on electron selective contacts are scarcely explored. In this work, we examine the impact of mesoporous TiO2 (m-TiO2) and planar TiO2 (p-TiO2) on the growth of single crystalline-methyl ammonium lead iodide (SC-MAPbI3) film, PSC device performance and film stability under harsh weather conditions (T ∼ 85 °C and RH ∼ 85%). Self-grown SC-MAPbI3 films are developed on m-TiO2 and p-TiO2 by inverse temperature crystallization under ambient conditions without the need for sophisticated glove-box processing. The best device with m-TiO2 as an electron transport layer showed a promising power conversion efficiency of 3.2% on an active area of 0.3 cm2 in hole transport material free configuration, whereas, only 0.7% was achieved for the films developed on p-TiO2. Complete conversion of precursor to perovskite phase and better surface coverage of the film leading to enhanced absorption and reduced defects of single crystalline perovskite on m-TiO2 compared to its p-TiO2 leads to this large difference in efficiency. Mesoporous device retained more than 70% of its initial performance when stored at 30 °C under dark for more than 5000 h at 50% RH; while the planar device degraded after 1500 h. Thermal and moisture endurance of SC-MAPbI3 films are investigated by subjecting them to temperatures ranging from 35 °C to 85 °C at a constant relative humidity (RH) of 85%. X-ray diffraction studies show that the SC-MAPbI3 films are stable even at 85 °C and 85% RH, with only slight detection (30-35%) of PbI2 at these conditions. This study highlights the superior stability of SC-MAPbI3 films which paves way for further studies on improving the stability and performance of the ambient processed PSCs.

Effect of solvent on the electronic absorption spectral properties of some mixed ß-octasubstituted Zn(II)-tetraphenylporphyrins.

A series of mixed ß-octasubstituted Zn(II)-porphyrins, 2,3,12,13-tetra(chloro/cyano/methyl)-5,7,8,10,15,17,18,20-octaphenylporphinato zinc(II), ZnTPP(Ph)4X4 (X=CN, Cl and CH3) have been examined by electronic absorption spectroscopy in various solvents. These Zn(II)-porphyrins exhibited varying degree of red-shift of absorption bands as high as 20-30nm in 'B' band and 50-60nm in longest wavelength band, 'Q(0,0)' band in polar solvents relative to that found in nonpolar solvents. The red-shift of B and Q(0,0) bands showed an unusual trend, ZnTPP(Ph)4(CN)4>ZnTPP(Ph)4(CH3)4>ZnTPP(Ph)4Cl4 but fails to follow an anticipated anodic shift in first porphyrin ring oxidation (vs Ag/AgCl) potential: ZnTPP(Ph)4(CN)4 (1.02V)>ZnTPP(Ph)4Cl4 (0.74V)>ZnTPP(Ph)4(CH3)4 (0.38V). Such a trend suggests the combined effect of non-planarity of the macrocycle and electronic effect of the peripheral substituents. The equilibrium constants for the binding of nitrogenous bases with the Zn(II)-porphyrins showed as high as twenty fold increase for ZnTPP(Ph)4X4 (X=Br and CN) relative to ZnTPP(Ph)4(CH3)4 and follow the order: ZnTPP(Ph)4(CN)4>ZnTPP(Ph)4Br4>ZnTPP(Ph)4(CH3)4≤ZnTPP which is approximately in line with an increase in anodic shift of their first ring redox potentials (ZnTPP(Ph)4(CN)4 (1.02V)>ZnTPP(Ph)4Br4 (0.72V)>ZnTPP (0.84V)>ZnTPP(Ph)4(CH3)4) (0.38V).

Planar and nonplanar free-base tetraarylporphyrins: ß-pyrrole substituents and geometric effects on electrochemistry, spectroelectrochemistry, and protonation/deprotonation reactions in nonaqueous media.

A series of planar and nonplanar free-base ß-pyrrole substituted meso-tetraarylporphyrins were characterized by electrochemistry, spectroelectrochemistry, and protonation or deprotonation reactions in neutral, acidic, and basic solutions of CH2 Cl2 . The neutral compounds are represented as H2 (P), in which P represents a porphyrin dianion with one of several different sets of electron-withdrawing or -donating substituents at the messo and/or ß-pyrrole positions of the macrocycle. The conversion of H2 (P) to [H4 (P)](2+) in CH2 Cl2 was accomplished by titration of the neutral porphyrin with trifluoroacetic acid (TFA) while the progress of the protonation was monitored by UV/Vis spectroscopy, which was also used to calculate logß2 for proton addition to the core nitrogen atoms of the macrocycle. Cyclic voltammetry was performed after each addition of TFA or TBAOH to CH2 Cl2 solutions of the porphyrin and half-wave potentials for reduction were evaluated as a function of the added acid or base concentration. Thin-layer spectroelectrochemistry was used to obtain UV/Vis spectra of the neutral and protonated or deprotonated porphyrins under the application of an applied reducing potential. The magnitude of the protonation constants, the positions of λmax in the UV/Vis spectra and the half-wave or peak potentials for reduction are then related to the electronic properties of the porphyrin and the data evaluated as a function of the planarity or nonplanarity of the porphyrin macrocycle. Surprisingly, the electroreduction of the diprotonated nonplanar porphyrins in acid media leads to H2 (P), whereas the nonplanar H2 (P) derivatives are reduced to [(P)](2-) in CH2 Cl2 containing 0.1 M tetra-n-butylammonium perchlorate (TBAP). Thus, in both cases an electrochemically initiated deprotonation is observed.

Mixed ß-pyrrole substituted meso-tetraphenylporphyrins and their metal complexes: optical nonlinearity using degenerate four wave mixing technique.

We have investigated the roles of structural modification and polar effects in the optical nonlinearities of a series of selectively mixed ß-pyrrole functionalized tetraphenylporphyrin, MTPP(CHO)(R)2 (R = H, Br, 2-thienyl, phenyl (Ph), phenylethynyl (PE) compounds and their metal (Cu(II), Zn(II)) complexes in toluene. In the present study, we have used phase conjugation geometry of the four wave mixing process to measure the third order nonlinear susceptibility (χ(3)) and the second order hyperpolarizabilty ((γ)) with picosecond laser pulse excitation at 532 nm. An increase in the values of χ(3) and (γ) for electron-withdrawing groups was observed whereas an opposite trend was noticed for the electron-donating groups at the ß-pyrrole positions. In the Cu(II) and Zn(II) complexes of substituted free base porphyrins, the distortion of the macrocyclic ring may be responsible for the reduction of the values of χ(3) and (γ). From fluorescence measurements, it has been found that the electron-donating and electron-withdrawing substituted groups at ß-pyrrole positions and also the macrocyclic ring distortion of the porphyrin lead to increased radiationless transitions.

Porphyrin-fullerene, C60, cocrystallates: influence of C60 on the porphyrin ring conformation.

To examine the influence of fullerene on the macrocyclic ring conformation, crystal structures of a series of cocrystals of 2,3,5,10,12,13,15,20-octaphenylporphyrin, M(TPP)(Ph)(4) (M = 2H, Co(II), Cu(II)), and 2,312,13-tetramethyl-5,7,8,10,15,17,18,20-octaphenyl-porphinato copper(II), CuTPP(Ph)(4)(CH(3))(4), derivatives with fullerene, C(60), were elucidated. Furthermore, crystal structures of the parent porphyrins, M(TPP)(Ph)(4) (M = Co(II), Cu(II)) complexes, were also determined. All the cocrystals revealed one-to-one stoichiometry between the porphyrin and C(60) and were free of lattice solvates. Porphyrin rings in M(TPP)(Ph)(4)·C(60) cocrystals revealed significant distortion with the root-mean-square (rms) value as high as 0.265(2) A which is the average deviation of the 24 atoms core from the least-squares plane. Crystal structures of the parent M(TPP)(Ph)(4) (M = Co(II), Cu(II)) complexes indicated near planarity of the 24-atom core with the root-mean-square deviation value of 0.016(2) A. Molecular packing in the M(TPP)(Ph)(4)·C(60) cocrystals showed essentially one-dimensional chains interconnected by weak interporphyrin and porphyrin-fullerene close contacts. The N(porphyrin)···C(C(60)) shortest distances between the H(2)(TPP)(Ph)(4) (M = 2H, Co(II), Cu(II)) and fullerene in the cocrystals are 3.031(5) A, 3.062(4) A, and 3.059(3) A, respectively. Similarly, close contact M···C distances in the M(TPP)(Ph)(4)·C(60) (M = Co(II), Cu(II)) are 2.761(6) A and 2.886(3) A, respectively. In the Cu(TPP)(Ph)(4)(CH(3))(4)·C(60) cocrystal, the shift of macrocyclic ring toward planarity was evidenced from the rms value of 0.236(2) A relative to that observed in CuTPP(Ph)(4)(CH(3))(4)·CHCl(3) (0.391(2) A). The distortion of the macrocyclic ring in M(TPP)(Ph)(4)·C(60) complexes was examined by normal-coordinate-structure decomposition (NSD) analyses. Their out-of-plane displacement of the core atoms revealed predominant contribution being saddle (∼95-96%) and gentle domed distortions (3-4%). In the case of M(TPP)(Ph)(4)(CH(3))(4)·C(60) cocrystal, it showed mainly saddled (∼83%), minimal ruffled (8%) and domed (8%) distortions of the macrocyclic ring. In-plane displacement on the 24-atom core of the porphyrin in these cocrystallates features generally a varying degree of N-str (B(1g)) and bre (A(1g)) distortions.

Influence of mixed substituents on the macrocyclic ring distortions of free base porphyrins and their metal complexes.

Crystal structures of a series of free base porphyrins, 2,3,12,13-tetra(cyano/chloro/bromo)-5,7,8,10,15,17,18,20-octaphenylporphyrin solvates [H(2)(TPP(Ph)(4)(CN)(4)) x 3 (C(2)H(4)Cl(2)), H(2)(TPP(Ph)(4)Cl(4)) x 2 (CH(3)OH), and H(2)(TPP(Ph)(4)Br(4)) x 2 THF x 1.5 (CH(3)OH)], were determined to examine the influence of mixed antipodal beta-pyrrole substitution on the stereochemistry of the porphyrin macrocycle. Nonplanarity of the porphyrin skeleton increases with an increase in size of the X group at the beta-pyrrole positions, and the root-mean-square deviation of the core atoms follows the order CN (0.508 A) < Cl (0.687 A) < Br (0.792 A). The normal-coordinate decomposition analysis of the free-base structures shows dramatic substituent- (X-)dependent out-of-plane distortions featuring saddling combined with a ruffled conformation in H(2)(TPP(Ph)(4)(CN)(4)), while it is predominantly saddled geometry in H(2)(TPP(Ph)(4)X(4)) (X = Cl, Br) structures. For H(2)(TPP(Ph)(4)X(4)) (X = Cl, Br) structures, the core elongation is along the antipodal pyrroles bearing halogen groups, and in the case of the H(2)(TPP(Ph)(4)(CN)(4)) structure, it is along the other antipodal pyrroles with phenyl groups. However, the average core, N...N separation along the transannular pyrrole direction follows the trend H(2)(TPP(Ph)(4)(CN)(4)) (4.134(4) A) < H(2)(TPP(Ph)(4)Cl(4)) (4.184(5) A) < H(2)(TPP(Ph)(4)Br(4)) (4.205(5) A). The bond lengths of the 24-atom core are comparable, but its bond angles showed significant differences along the antipodal direction bearing beta-pyrrole with X groups when compared to the other transannular pyrrole direction. The four-nitrogen porphyrin core (N(4)H(2)) exhibited weak intramolecular hydrogen bonding and also intermolecular interactions. Interestingly, H(2)(TPP(Ph)(4)Cl(4)) x 2 (CH(3)OH) shows an extended chain structure involving hydrogen-bonding interactions between the CH(3)OH...OHCH(3) (O...O) and CH(3)OH...core (N(4)H(2)) interactions. The nonplanar geometry of these free base porphyrin rings suggests a more predominant influence of steric crowding of the peripheral substituents rather than intermolecular interactions. The four-coordinated Ni(TPP(Ph)(4)(CN)(4)) x C(6)H(14) x 0.5 (C(2)H(4)Cl(2)) complex shows an enhanced ruffling of the macrocycle along with the saddled conformation relative to more saddle-shaped H(2)(TPP(Ph)(4)(CN)(4)) x 3 (C(2)H(4)Cl(2)) structure. The crystal structure of the Zn(TPP(Ph)(4)Cl(4))(Py) x (C(2)H(4)Cl(2)) complex features distorted square-pyramidal geometry with the reduction in the nonplanarity of the core in contrast to its free base porphyrin structure. Normal-coordinate-decomposition analysis for the out-of-plane displacement of the core atoms in the Ni(TPP(Ph)(4)(CN)(4)) structure showed enhanced ruffling combined with saddling of the macrocycle while Zn(TPP(Ph)(4)Cl(4))(Py) exhibited mainly saddling when compared to their corresponding free base porphyrin structures. The nonplanar distortion in the Ni(TPP(Ph)(4)(CN)(4)) x (C(6)H(14)) x 0.5 (C(2)H(4)Cl(2)) complex indicates that the contracted porphyrin core and the weak intermolecular interactions are responsible for the nonplanar geometry of the macrocyclic ring.

Functionalized Au22 clusters: synthesis, characterization, and patterning.

We synthesized fluorescent, porphyrin-anchored, Au(22) clusters in a single step, starting from well-characterized Au(25) clusters protected with glutathione (-SG) by a combined core reduction/ligand exchange protocol, at a liquid-liquid interface. The prepared cluster was characterized by UV/vis, photoluminescence, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy, elemental analysis, and matrix-assisted laser desorption ionization mass spectrometry. The absence of a 672 nm intraband transition of Au(25) and the simultaneous emergence of new characteristic peaks at 520 and 635 nm indicate the formation of the Au(22) core. An increase in the binding energy of 0.4 eV in Au 4f core-level peaks confirmed the presence of a reduced core size. Quantitative XPS confirmed the Au/S ratio. The presence of a free base, tetraphenylporphyrin (H(2)TPPOAS-), on the Au(22) core was confirmed by fluorimetric titrations with Cu(2+) and Zn(2+) ions. From all of these, the composition of the cluster was determined to be Au(22)[(-SG)(15)(-SAOPPTH(2))(2)], which was supported by mass spectrometry and elemental analysis. We utilized the fluorescence nature of these water-soluble clusters for the fabrication of fluorescent patterns by soft lithography. The patterns were studied using tapping-mode atomic force microscopy and confocal fluorescence imaging.

2,3,12,13-Tetrabromo-5,10,15,20-tetrakis(4-butoxyphenyl)porphyrin 1,2-dichloroethane solvate.

Nonmesogenic 2,3,12,13-tetrabromo-5,10,15,20-tetrakis(4-butoxyphenyl)porphyrin crystallizes as the title 1,2-dichloroethane solvate, C(60)H(58)Br(4)N(4)O(4) x C(2)H(4)Cl(2). The porphyrin ring shows a nonplanar conformation, with an average mean plane displacement of the beta-pyrrole C atoms from the 24-atom (C(20)N(4)) core of +/-0.50 (3) A. The 1,2-dichloroethane solvent is incorporated between the porphyrin units and induces the formation of one-dimensional chains via interhalogen Cl...Br and butyl-aryl C-H...pi interactions. These chains are oriented along the unit-cell a axis, with the macrocyclic ring planes lying almost parallel to the (010) plane. The chains are arranged in an offset fashion by aligning the butoxy chains approximately above or below the faces of the adjacent porphyrin core, resulting in decreased interporphyrin pi-pi interactions, and they are held together by weak intermolecular (C-Br...pi, C-H...pi and C-H...Br) interactions. The nonplanar geometry of the macrocyclic ring is probably due to the weak interporphyrin interactions induced by the solvent molecule and the peripheral butoxy groups. The nonplanarity of the mesogens could influence the mesogenic behaviour differently relative to planar porphyrin mesogens.

5,10,15,20-Tetra-kis(3,5-difluoro-phen-yl)porphyrin.

The crystal structure of the title compound, C(44)H(22)F(8)N(4), shows an unusual non-planar geometry of the porphyrin ring although the mol-ecule is free of steric crowding around the periphery of the macrocycle. The mol-ecular packing exhibits weak inter-molecular hydrogen bonding (C-H⋯F) and C-H⋯π inter-actions. The molecular symmetry is .

C(60) 1,1,2,2-tetra-chloro-ethyl-ene tetra-solvate.

In the title complex, C(60)·4C(2)Cl(4), the C(60) mol-ecule is located on an inversion centre and there are two tetra-chloro-ethyl-ene (TCE) mol-ecules in the asymmetric unit. Both TCE mol-ecules show positional disorder, with occupancy ratios of 0.75:0.25 and 0.56:0.44. Four fullerene C atoms form short contacts [3.208 (17) and 3.223 (17) Å] with the centres of the TCE double bonds, indicating that C(60)-solvent inter-actions are largely π-π in nature.

Mixed substituted porphyrins: structural and electrochemical redox properties.

To examine the influence of mixed substituents on the structural, electrochemical redox behavior of porphyrins, two new classes of beta-pyrrole mixed substituted free-base tetraphenylporphyrins H2(TPP(Ph)4X4) (X = CH3, H, Br, Cl, CN) and H2(TPP(CH3)4X4) (X = H, Ph, Br, CN) and their metal (M = Ni(II), Cu(II), and Zn(II)) complexes have been synthesized effectively using the modified Suzuki cross-coupling reactions. Optical absorption spectra of these porphyrins showed significant red-shift with the variation of X in H2(TPPR4X4), and they induce a 20-30 nm shift in the B band and a 25-100 nm shift in the longest wavelength band [Q(x)(0,0)] relative to the corresponding H2TPPR4 (R = CH3, Ph) derivatives. Crystal structure of a highly sterically crowded Cu(TPP(Ph)4(CH3)4).2CHCl3 complex shows a combination of ruffling and saddling of the porphyrin core while the Zn(TPP(Ph)4Br4(CH3OH)).CH3OH structure exhibits predominantly saddling of the macrocycle. Further, the six-coordinated Ni(TPP(Ph)4(CN)4(Py)2).2(Py) structure shows nearly planar geometry of the porphyrin ring with the expansion of the core. Electrochemical redox behavior of the MTPPR4X4 compounds exhibit dramatic cathodic shift in first ring oxidation potentials (300-500 mV) while the reduction potentials are marginally cathodic in contrast to their corresponding MTPPX4 (X = Br, CN) derivatives. The redox potentials were analyzed using Hammett plots, and the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap decreases with an increase in the Hammett parameter of the substituents. Electronic absorption spectral bands of H2TPPR4X4 are unique that their energy lies intermediate to their corresponding data for the H2(TPPX8) (X = CH3, Ph, Br, Cl) derivatives. The dramatic variation in redox potentials and large red-shift in the absorption bands in mixed substituted porphyrins have been explained on the basis of the nonplanarity of the macrocycle and substituent effects.

Microporous porphyrin solids.

Metalloporphyrins are exceedingly useful building blocks for the design and synthesis of molecularly based solids. The use of hydrogen bonding or metal ion coordination provides a wide range of framework solids. Using various polyfunctionalized porphyrins, we have created porous solids that are thermally robust and that retain their internal porosity upon loss of solvates. Their pore dimensions are comparable to zeolites, and they show shape and size selectivity in sorption of guest molecules and in epoxidation of alkenes.

[5,10,15,20-Tetrakis(2-thienyl)-porphyrinato]zinc(II).

In the title complex, [Zn(C(36)H(20)N(4)S(4))], the Zn(II) ion occupies a special position on an inversion centre with four-coordinate geometry. The porphyrin ring shows a wave-like conformation, with the closest interporphyrin plane separation being 3.60 (6) A. The two disordered thienyl groups are inclined with respect to the porphyrin plane at angles of 70 (4) and 67 (2) degrees.