Self-Assembled Monolayers of Bi-Functionalized Porphyrins: A Novel Class of Hole-Layer-Coordinating Perovskites and Indium Tin Oxide in Inverted Solar Cells.

Self-assembled monolayers (SAMs) offer the advantage of facile interfacial modification, leading to significant improvements in device performance. In this study, we report the design and synthesis of a new series of carboxylic acid-functionalized porphyrin derivatives, namely AC-1, AC-3, and AC-5, and present, for the first time, a strategy to exploit the large π-moiety of porphyrins as a backbone for interfacing the indium tin oxide (ITO) electrode and perovskite active layer in an inverted perovskite solar cell (PSC) configuration. The electron-rich nature of porphyrins facilitates hole transfer and the formation of SAMs, resulting in a dense surface that minimizes defects. Comprehensive spectroscopic and dynamic studies demonstrate that the double-anchored AC-3 and AC-5 enhance SAMs on ITO, passivate the perovskite layer, and function as conduits to facilitate hole transfer, thus significantly boosting the performance of PSCs. The champion inverted PSC employing AC-5 SAM achieves an impressive solar efficiency of 23.19 % with a high fill factor of 84.05 %. This work presents a novel molecular engineering strategy for functionalizing SAMs to tune the energy levels, molecular dipoles, packing orientations to achieve stable and efficient solar performance. Importantly, our comprehensive investigation has unraveled the associated mechanisms, offering valuable insights for future advancements in PSCs.

Thermally Stable D2h Symmetric Donor-π-Donor Porphyrins as Hole-Transporting Materials for Perovskite Solar Cells.

A series of new D2h symmetric porphyrins (MDA4, MTA4, and MDA8) with donor-π-donor structures have been synthesized as the hole-transporting materials for perovskite solar cells (PSCs). The novel porphyrin molecules feature a D2h symmetrically substituted ZnII porphyrin core and two kinds of donor systems (diarylamine (DAA) and triarylamine (TAA)), which can regulate energy level, increase thermal stability, solubility, and hydrophobicity via long alkoxyl chains. PSC devices based on MDA4 as the HTM showed impressive power-conversion efficiency (PCE) of 22.67 % under AM1.5G solar illumination. Notably, the device was sent for certification, and a PCE of 22.19 % was reported, representing the highest PCE from porphyrin-based HTMs. Furthermore, the MDA4-based PSCs showed excellent thermal stability under 60 °C and RH 60 % and preserved 88 % of initial performance after 360 hours. The strategy opens a new avenue for developing efficient and stable porphyrin HTMs for PSCs.

NdCl3 Dose as a Universal Approach for High-Efficiency Perovskite Solar Cells Based on Low-Temperature-Processed SnOx.

The defects on the surface of low-temperature-processed electronic transport layers hindered the development of efficient flexible perovskite solar cells. Herein, we develop a universal NdCl3 dosing strategy to circumvent the residual Sn(II)-OH defects from the incomplete wet-chemical reaction. The introduction of NdCl3 does not lead to the doping of Nd3+ ions but rather the formation of a composite film of NdCl3 with SnOx. The dose of NdCl3 effectively reduces surface trap states at low-temperature-processed SnOx films, leading to increased carrier extraction and reduced carrier accumulation/recombination at the ETL/perovskite interface. These improvements result in perovskite solar cells (PvSCs) with significantly enhanced power conversion efficiency (PCE) and eliminated hysteresis. Finally, efficiencies of 18.62% and 21.49% for PvSCs based on MAPbI3 and FA1-xMAxPbI3 perovskites, respectively, were achieved on rigid substrates. The test on a flexible device based on Cs0.05(FA0.83MA0.17)0.95(I0.83Br0.17)3 perovskite realized a PCE of 16.14% and an incredible VOC of 1.158 V. This study indicated the potential of NdCl3 dose as a universal approach to enhance the performance of PvSCs with low-temperature-processed SnOx ETL.

Lewis-base containing spiro type hole transporting materials for high-performance perovskite solar cells with efficiency approaching 20.

Owing to excellent performance and dopability, spiro-OMeTAD remains an irreplaceable hole transporting material (HTM) in perovskite solar cells (PSCs). In order to further improve the performance of spiro-OMeTAD based PSCs, a Lewis base can be introduced into the structure of spiro-OMeTAD wisely, which can keep the advantages of spiro-OMeTAD while incorporating the functionality of a Lewis base in passivating the surface of the perovskite. Therefore, spiro-type HTMs (spiro-CN-OMeTAD with a dicyano group and spiro-PS-OMeTAD with a thiocarbonyl group) were synthesized and confirmed by density functional theory (DFT) calculations and X-ray single-crystallographic diffraction. Spiro-CN-OMeTAD as an HTM is certified to have a suitable interfacial band alignment with the perovskite, good film quality and effective defect passivation, which facilitate the resulting device to achieve an efficiency of 19.90% with a high open-circuit voltage, low hysteresis, and improved stability. This study provides an alternative strategy for the molecular design of better HTMs in high-performance PSCs.

Function of Tetrabutylammonium on High-Efficiency Ruthenium Sensitizers for Both Outdoor and Indoor DSC Application.

The function of tetrabutyl ammonium ions (TBA+) in a sensitizer used in dye-sensitized solar cells (DSC) is contradictory. TBA+ can reduce unwanted charge-recombination by protecting the TiO2 surface and reduce dye aggregation, enhancing the photovoltaic performance. It will also compete with the dye-loading on the TiO2 film, decreasing the short-circuit current density of the cell. Three ruthenium sensitizers (DYE III, DUY11, and DUY12 containing two H+, one H+/one TBA+, and two TBA+, respectively) were prepared to systematically investigate the function of TBA+ in a dye for DSC under both standard sunlight and indoor illumination. The optical properties and frontier orbital energy level of the sensitizers are not influenced significantly by the number of TBA+. Under the standard 1 sun illumination, DSCs based on DUY11 (containing one H+ and one TBA+) achieved the highest power conversion efficiency (PCE) of 11.47%. Overall, optimized DSCs sensitized by the three ruthenium dyes all have the PCE over 10%, which is higher than that (9.95%) of N719-dyed cell fabricated at the same conditions. Under the illumination of a light emitting diode (LED), DSCs sensitized by DUY11 also have the highest efficiency of 19%. Furthermore, DUY12 with two TBA+ exhibits superior photovoltaic performance compared to a DYE III (containing two H+ in the anchoring ligands)-dyed cell; although these two dyes have similar photovoltaic performance under standard 1 sun lighting. The important function of TBA+ in reducing the charge recombination (by protecting TiO2 surface and avoiding dye aggregation) of a DSC under indoor lighting (when small number of electrons were excited by weak light) is also revealed.

Synthesis of Octafluoroporphyrin.

Despite the long list of known fluoroporphyrinoids, the most fundamental 2,3,7,8,12,13,17,18-octafluoroporphyrin (OFP) has not been synthesized until now. It is achieved by condensation of two molecules of tetrafluoro-dipyrrylmethane-2-carboxaldehyde in the presence of magnesium(II) salts. The fluorinated dipyrrylmethane also gives 5,15-bis(pentafluorophenyl)-OFP (F18P) with a reasonable yield. Both Mg/OFP and Zn/F18P in the solid-state reveal an essentially flat structure. The fluoro groups impart as much as a 0.5 V anodic shift for porphyrin ring oxidation/reduction, as well as hypsochromic shifts in the Uv-vis spectra.

Porphyrin Sensitizers Bearing a Pyridine-Type Anchoring Group for Dye-Sensitized Solar Cells.

Three novel efficient donor-acceptor porphyrins, MH1-MH3, with a pyridine-type acceptor and anchoring group were synthesized and their optical, electrochemical, and photovoltaic properties investigated. Replacing the commonly used 4-carboxyphenyl anchoring group with 2-carboxypyridine, 2-pyridone, and pyridine did not significantly change the absorption and electrochemical properties of the porphyrin dyes. These new porphyrin dyes MH show power conversion efficiencies of 8.3%, 8.5%, and 8.2%, which are comparable to that of the benchmark YD2-o-C8 (η=8.25%) under similar conditions. It was demonstrated that 2-carboxypyridine is an efficient and stable anchoring group as MH1 and showed better cell performance and long-term stability than YD2-o-C8 under light soaking conditions.

Molecular engineering of push-pull porphyrin dyes for highly efficient dye-sensitized solar cells: the role of benzene spacers.

Porphyrins have drawn much attention as sensitizers owing to the large absorption coefficients of their Soret and Q bands in the visible region. In a donor and acceptor zinc porphyrin we applied a new strategy of introducing 2,1,3-benzothiadiazole (BTD) as a π-conjugated linker between the anchoring group and the porphyrin chromophore to broaden the absorption spectra to fill the valley between the Soret and Q bands. With this novel approach, we observed 12.75% power-conversion efficiency under simulated one-sun illumination (AM1.5G, 100 mW cm(-2)). In this study, we showed the importance of introducing the phenyl group as a spacer between the BTD and the zinc porphyrin in achieving high power-conversion efficiencies. Time-resolved fluorescence, transient-photocurrent-decay, and transient-photovoltage-decay measurements were employed to determine the electron-injection dynamics and the lifetime of the photogenerated charge carriers.

Facile synthesis of heterotrimetallic metal-string complex [NiCoRh(dpa)4Cl2] through direct metal replacement.

This communication provides a practical strategy for the synthesis of heterotrimetallic extended metal atom chains with supported dpa(-) ligands. The transformation of the CoCoRh to a NiCoRh trinuclear complex can be achieved by direct metallic replacement. Furthermore, the first (CoRh)(4+) metal-metal bond is described here.

Synthesis and characterization of diporphyrin sensitizers for dye-sensitized solar cells.

Novel porphyrin dimers with broad and strong absorption in the visible and/or near IR regions have been synthesized; the meso-meso-linked porphyrin dimer (YDD1) exhibited the best photovoltaic performance with power conversion efficiency 5.2% under AM 1.5G one solar illumination.

Design and characterization of highly efficient porphyrin sensitizers for green see-through dye-sensitized solar cells.

YD12 (eta = 6.7%) is a green sensitizer remarkable for its outstanding cell performance beyond that of N719 (eta = 6.1%) with no added scattering layer; the additional scattering layer assists N719 in promoting the efficiency in the red shoulder of the spectrum, but has only a small effect on the improvement of the cell performance for porphyrins.

A waterwheel-shaped meso-meso-linked porphyrin pentamer.

Wheels on water? A waterwheel-shaped porphyrin pentamer has been synthesized by palladium-catalyzed cross-coupling reactions. The key intermediate is a boronate porphyrin, in which four boronic ester groups are directly attached to the meso-positions.

Structure-property relationship for two-photon absorbing multiporphyrins: supramolecular assembly of highly-conjugated multiporphyrinic ladders and prisms.

Two-photon absorption (TPA) phenomena of a series of single-strand as well as supramolecular self-assembled ladders and prisms of highly conjugated ethyne bridged multiporphyrin dimer, trimer, and star shaped pentamer have been investigated. The ligand mediated self-assembled supramolecular structures were characterized by UV-visible spectroscopy and small- and wide-angle X-ray scattering (SAXS/WAXS) analysis. The TPA cross section values of multiporphyrins increase nonlinearly from approximately 100 to approximately 18000 GM with an increased number of porphyrin units and elongated pi-conjugation length by virtue of charge transfer and excited-state cumulenic configurations. The observed opposite TPA behavior between their supramolecular ladder and prism configurations necessitates the importance of interstrand interactions between the multiporphyrinic units and the overall shape of the assembly. Furthermore, the diminished TPA cross section of the pentamer, despite the increased pi-conjugation resulting from duplex formation suggests that destabilizing the essential functional configurations at the cost of elongation of pi-delocalization pathway must cause unfavorable effects. We have also shown that one- and two-photon allowed energy-levels of linear multiporphyrins are nearly isoenergetic and the latter transition originates exclusively from the extent of pi-delocalization within the molecule. The identical TPA maximum position of the trimer and pentamer indicates that the TPA of the pentamer arises only from its basic trimer unit in spite of its extended two-dimensional pi-conjugation pathway involving five porphyrinic units.

Synthesis, structure, and optical and electrochemical properties of star-shaped porphyrin-triarylamine conjugates.

A series of novel star-shaped porphyrin-triarylamine conjugates were synthesized by palladium-catalyzed cross-coupling reactions. The spectroscopic and electrochemical studies show that pi-conjugation of the porphyrin core is extended to the triarylamine moieties.

Highly conjugated multiporphyrins: synthesis, spectroscopic and electrochemical properties.

A series of meso-to-meso ethynyl-bridged multiporphyrin arrays have been synthesized using Sonogoshira palladium-catalyzed cross-coupling reactions involving the appropriate ethynylporphyrin and iodoporphyrin precursors. The absorption spectra of these multiporphyrins show splitting of the Soret bands and significant red shifts of the Q bands as compared to the combination of the corresponding components. These conjugated multiporphyrins also show red shifts in their emission spectra as the pi-conjugation is expanded. In the electrochemical measurements, the porphyrins dimer 7 shows two 1 - e- oxidations at E(1/2) = +0.63 and +0.76 V for the first electron abstraction from the two porphyrin rings, indicating electronic communication between the two porphyrin units. The porphyrin trimer 4 exhibits the first and second 1 - e- oxidations at E(1/2) = +0.68 and +0.77 V, respectively, which correspond to the two outer porphyrins. The cyclic voltammogram of pentamer 5 shows two overlapping 1 - e- couples at E(1/2) = +0.56 and +0.66 V, and one 2 - e- couple at E(1/2) = +0.86 V, for the four outer porphyrin units. These results demonstrate that in the porphyrin trimer and pentamer the individual peripheral porphyrin units are electrochemically coupled via a central porphyrin core. The UV-Vis-NIR spectra of the oxidized species of these multiporphyrins exhibit a broad intervalence charge transfer (IVCT) band in the region from 1200 to 3000 nm. The present work shows that a central porphyrin unit appended with ethynyl bridges affords strong electronic interactions between the peripheral porphyrin rings over a distance of about 15 A.