Determination of the Attenuation Factor () in Hybrid Covalent/Non-Covalent Molecular Wires

We have established for the first time the molecular wire behaviour in a new set of hybrid covalent/supramolecular porphyrinfullerene structures, in which hydrogen-bond interactions and pphenylene oligomers of different length act as highly efficient molecular wires exhibiting a remarkably low attenuation factor ( = 0.07 ± 0.01 Å1 )

High-Efficiency Perovskite Solar Cells using Molecularly-Engineered, Thiophene-Rich,Hole-Transporting Materials: Influence of Alkyl Chain Length on Power Conversion Efficiency

The synthesis and characterization of a series of novel small-molecule hole-transporting materials (HTMs) based on an anthra[1,2-b:4,3-b′:5,6-b′′:8,7-b′′′]tetrathiophene (ATT) core are reported. The new compounds follow an easy synthetic route and have no need of expensive purification steps. The novel HTMs were tested in perovskite solar cells (PSCs) and power conversion efficiencies (PCE) of up to 18.1 % under 1 sun irradiation were 2 measured. This value is comparable with the 17.8 % efficiency obtained using spiroOMeTAD as a reference compound. Similarly, a significant quenching of the Photoluminescence in the first nanosecond is observed, indicative of effective hole transfer.Additionally, the influence of introducing aliphatic alkyl chains acting as solubilizers on the device performance of the ATT molecules is investigated. Replacing the methoxy groups on the triarylamine sites by butoxy-, hexoxy- or decoxy-substituents greatly improved the solubility of the compounds without changing the energy levels, yet at the same time significantly decreasing the conductivity as well as the PCE, 17.3 % for ATT-OBu, 15.7 % for ATT-OHex and 9.7 % for ATT-ODec

Analysis of the Hysteresis Behavior of Perovskite Solar Cells with Interfacial Fullerene Self-Assembled Monolayers

The use of self-assembled monolayers (SAMs) of fullerene derivatives reduces the hysteresis of perovskite solar cells (PSCs). We have investigated three different fullerene derivatives observing a decrease on hysteresis for all the cases. Several processes can contribute to the hysteresis behavior on PSCs. We have determined that the reduced hysteresis observed for devices with SAMs is produced by a decrease of the capacitive hysteresis. In addition, with an appropriated functionalization, SAMs can increase photocurrent even when no electron selective contact (ESC) is present and a SAM is deposited just on top of the transparent conductive oxide. Appropriated functionalization of the fullerene derivative, as introducing −CN groups, can enhance cell performance and reduce hysteresis. This work paves the way for a future enhancement of PSCs by a tailored design of the fullerene molecules that could actuate as an ESC by themselves

Spiro-derivatives as hole transporting materials for improving the performance of perovskite solar cells

The Sun is the most powerful source of energy in the Earth's solar system, which, in part, can be exploited by all the inhabitants of the Earth. The optimal exploitation of the fraction that arrives on earth is, undoubtedly, among the most important challenges nowadays of science. To convert sun light into chemical energy, the first silicon-based device Photovoltaic (PV) solar cells, prepared by Chapin in 1954 exhibiting an efficiency around 6% [1,2] used different semiconducting materials (inorganic, organic, molecular, polymeric, hybrids, quantum dots, etc.). Today the most promising technology to replace/complement crystalline silicon PV [3] are the Perovskites solar cells (PSCs) that emerged since 2009, achieving efficiencies of ~26 %. These results were obtained using commercially available spiro-OMeTAD as hole-transporting material (HTM) that are expensive materials due to its difficult purification and multi-step synthetic protocols (in harsh conditions) which limits its future use in large-scale applications. Considering the negative aspects related to the industrial production of the spiro-OMeTAD, we synthesized some intermediates necessary for the subsequent synthesis of four spiro-derivatives. Excellent results were obtained with some derivatives based on electron-rich spiranic scaffolds [4], synthesized by the Buchwald-Hartwig reaction, carried out in toluene. In this way it was possible to obtain the spiro-PTZ functionalized, by making structural modifications to the previously obtained derivatives, the yield of this synthesis was around 21%. The compounds obtained were incorporated into perovskite solar cells providing efficiencies higher than the standard used (spiroOMeTAD). The devices have been tested under illumination and have shown good stability over time

High Photo-Current in Solution Processed Organic Solar Cells Based on Porphyrin Core A-π-D-π-A as Electron Donor Material

Two new conjugated acceptor-donor-acceptor (A-p-D-p-A) molecules with a porphyrin core linked by ethynylene bridges to two thiophene (1a) or thienylenevinylenethiophene (1b) units and both capped by N-ethylrhodanine have been synthesized. These compounds were used as the main electron donor moieties for bulk heterojunction small molecule organic solar cells (BHJ-SMOSC). The optimized devices, with PC71BM as the main electron acceptor molecule, show remarkable short circuit currents, up to 13.2 mA/cm2, an open circuit voltage of around 0.85 V, and power conversion efficiencies up to 4.3% under 100 W/cm2. The External Quantum Efficiency (EQE), Atomic Force Microscopy (AFM), hole mobility, Photo-Induced Charge Extraction (PICE) and Photo-Induced Transient Photo-Voltage (PIT-PV) were analyzed in devices based on 1a and 1b in order to account for differences in the final performance of the two molecules. The PIT-PV decays showed slower recombination kinetics for devices fabricated with 1b. Moreover, the EQE was greater for 1b and this is ascribed to the better nanomorphology, which allows better charge collection before carrier recombination takes place

A Trapezoidal Octacyanoquinoid Acceptor Forms Solution and Surface Products by Antiparallel Shape Fitting with Conformational Dipole Momentum Switch

A new compound (1) formed by two antiparallelly disposed tetracyano thienoquinoidal units has been synthesized and studied by electrochemistry, UV/Vis-NIR, IR, EPR, and transient spectroscopy. Self-assembly of 1 on a Au(111) surface has been investigated by scanning tunneling microscopy. Experiments have been rationalized by quantum chemical calculations. 1 exhibits a unique charge distribution in its anionic form, with a gradient of charge yielding a neat molecular in-plane electric dipole momentum, which transforms out-of-plane after surface deposition due to twisted! folded conformational change and to partial charge transfer from Au(111). Intermolecular van der Waals interactions and antiparallel trapezoidal shape fitting lead to the formation of an optimal dense on Au(111) two-dimensional assembly of 1. The realization of novel properties emerging upon electronic covalent coupling between chromophores (i.e., bichromophoric systems) is a critical issue for the development of photo- and electrically active systems.[1–3] In this regard, the relative topology and orientation of the p-subchromophores, such as in A + B type p-systems in Figure 1, with 1D linear conjugation, 2D parallel conjugation,[4] 3D orthogonal spiroconjugation[5] or 3D conjugation[6] are key factors. On the other hand, studies of the distribution of the excess of charge in p-conjugated moieties in post-electron transfer events are central issues in photophysics and photochemistry, in energy storage[7] and in organic electronics.[8] In addition to this electronic provision, its embedment in different molecular forms is of relevance as these can define unique ways of shape fitting in supramolecular and surface assemblies. Joint electronic and molecular shape designs thus allow to build molecular-based synthons in a tailored manner towards new bulk and nano organized materials. (...)Funding for open access charge: Universidad de Málaga / CBUA. The authors thank the Spanish Ministry of Science, Innovation and Universities MCIU (projects CTQ2017-83531-R, RED2018-102815-T, MAT2017-85089-C2-1-R), Centro de Excelencia Severo Ochoa grants (SEV-2016-0686, SEV2015-0496 and FUNFUTURE CEX2019-000917-S) and the CAM (QUIMTRONIC-CM project Y2018/NMT-4783). We thank MINECO/FEDER of the Spanish Government (projects PGC2018-098533-B-100 and PID2019-109555GB-I00), the Eusko Jaurlaritza (Basque Government, project PIBA19-0004) and the Junta de Andalucía, Spain (UMA18FEDERJA057). We also thank the Research Central Services (SCAI) of the University of Málaga and the Donostia International Physics Center (DIPC) Computer Center. We thank Dr. Juwon Oh and Prof. Donhgo Kim from the Spectroscopy Laboratory for Functional p-electronic Systems and Department of Chemistry, Yonsei University in Korea for the generous gift of the TRIR and UV/Vis transient absorption spectroscopy data

A Trapezoidal Octacyanoquinoid Acceptor Forms Solution and Surface Products by Antiparallel Shape Fitting with Conformational Dipole Momentum Switch

A new compound (1) formed by two antiparallelly disposed tetracyano thienoquinoidal units has been synthesized and studied by electrochemistry, UV/Vis-NIR, IR, EPR, and transient spectroscopy. Self-assembly of 1 on a Au(111) surface has been investigated by scanning tunneling microscopy. Experiments have been rationalized by quantum chemical calculations. 1 exhibits a unique charge distribution in its anionic form, with a gradient of charge yielding a neat molecular in-plane electric dipole momentum, which transforms out-of-plane after surface deposition due to twisted→folded conformational change and to partial charge transfer from Au(111). Intermolecular van der Waals interactions and antiparallel trapezoidal shape fitting lead to the formation of an optimal dense on Au(111) two-dimensional assembly of 1.The authors thank the Spanish Ministry of Science, Innovation and Universities MCIU (projects CTQ2017-83531-R, RED2018-102815-T, MAT2017-85089-C2-1-R), Centro de Excelencia Severo Ochoa grants (SEV-2016-0686, SEV-2015-0496 and FUNFUTURE CEX2019-000917-S) and the CAM (QUIMTRONIC-CM project Y2018/NMT-4783). We thank MINECO/FEDER of the Spanish Government (projects PGC2018-098533-B-100 and PID2019-109555GB-I00), the Eusko Jaurlaritza (Basque Government, project PIBA19-0004) and the Junta de Andalucía, Spain (UMA18FEDERJA057). We also thank the Research Central Services (SCAI) of the University of Málaga and the Donostia International Physics Center (DIPC) Computer Center. We thank Dr. Juwon Oh and Prof. Donhgo Kim from the Spectroscopy Laboratory for Functional π-electronic Systems and Department of Chemistry, Yonsei University in Korea for the generous gift of the TRIR and UV/Vis transient absorption spectroscopy data.Peer reviewe

Nanoelectrical analysis of single molecules and atomic-scale materials at the solid/liquid interface

Evaluating the built-in functionality of nanomaterials under practical conditions is central for their proposed integration as active components in next-generation electronics. Low-dimensional materials from single atoms to molecules have been consistently resolved and manipulated under ultrahigh vacuum at low temperatures. At room temperature, atomic-scale imaging has also been performed by probing materials at the solid/liquid interface. We exploit this electrical interface to develop a robust electronic decoupling platform that provides precise information on molecular energy levels recorded using in situ scanning tunnelling microscopy/spectroscopy with high spatial and energy resolution in a high-density liquid environment. Our experimental findings, supported by ab initio electronic structure calculations and atomic-scale molecular dynamics simulations, reveal direct mapping of single-molecule structure and resonance states at the solid/liquid interface.We further extend this approach to resolve the electronic structure of graphene monolayers at atomic length scales under standard room-temperature operating conditions

Diarylamino-substituted Tetraarylethene (TAE) as Efficient and Robust Hole Transport Material for 11% Methyl Ammonium Lead Iodide Perovskite Solar Cells.

We report the synthesis and characterisation of tetra{4-[N,N-(4,4′-dimethoxydiphenylamino)]phenyl}ethene (TAE-1) as an efficient and robust hole transport material for its application in methyl ammonium lead iodide (MAPI) perovskite solar cells. The solar cells show light-to-energy conversion efficiencies as high as 11.0% under standard measurement conditions without the need of additional dopants

Single-Molecule Junctions with Epitaxial Graphene Nanoelectrodes

On the way to ultraflat single-molecule junctions with transparent electrodes, we present a fabrication scheme based on epitaxial graphene nanoelectrodes. As a suitable molecule, we identified a molecular wire with fullerene anchor groups. With these two components, stable electrical characteristics could be recorded. Electrical measurements show that single-molecule junctions with graphene and with gold electrodes display a striking agreement. This motivated a hypothesis that the differential conductance spectra are rather insensitive to the electrode material. It is further corroborated by the assignment of asymmetries and spectral features to internal molecular degrees of freedom. The demonstrated open-access graphene electrodes and the electrode-insensitive molecules provide a model system that will allow for a thorough investigation of an individual single-molecule contact with additional probes