Tripodal Triazatruxene Derivative as a Face-On Oriented Hole-Collecting Monolayer for Efficient and Stable Inverted Perovskite Solar Cells.

Hole-collecting monolayers have drawn attention in perovskite solar cell research due to their ease of processing, high performance, and good durability. Since molecules in the hole-collecting monolayer are typically composed of functionalized π-conjugated structures, hole extraction is expected to be more efficient when the π-cores are oriented face-on with respect to the adjacent surfaces. However, strategies for reliably controlling the molecular orientation in monolayers remain elusive. In this work, multiple phosphonic acid anchoring groups were used to control the molecular orientation of a series of triazatruxene derivatives chemisorbed on a transparent conducting oxide electrode surface. Using infrared reflection absorption spectroscopy and metastable atom electron spectroscopy, we found that multipodal derivatives align face-on to the electrode surface, while the monopodal counterpart adopts a more tilted configuration. The face-on orientation was found to facilitate hole extraction, leading to inverted perovskite solar cells with enhanced stability and high-power conversion efficiencies up to 23.0%.

Triptycene End-Capping as Strategy in Materials Chemistry to Control Crystal Packing and Increase Solubility.

In materials chemistry of polycyclic aromatic compounds (PACs) the kind of aggregation and the spatial arrangement of the π-planes are of utmost importance, e. g. for charge transport properties. Unfortunately, controlling these during crystallization is not trivial. In the past decade, we have introduced one-fold triptycene end-capping of quinoxalinophenanthrophenazines (QPPs) and other related structures to overcome this problem. When two instead of one triptycene end-caps are introduced, packing is largely suppressed, making typical PACs or pigments soluble in common organic solvents - which is another important property for such compounds to be processable from solution. In this account an overview of our research on using triptycene end-capping as dual strategy is given.

Synthesis and Optoelectronic Properties of a Quinoxalino-Phenanthrophenazine (QPP) Extended Tribenzotriquinacene (TBTQ).

A six-step synthesis towards a tribenzotriquinacene (TBTQ) bearing three quinoxalinophenanthrophenazine (QPP) units is presented. The optoelectronic properties are investigated and the effect of the three-dimensional arrangement of the individual QPP planes is examined using optical spectroscopy, electrochemical analysis and quantum-chemical calculations.

Triptycene End-Capped Benzothienobenzothiophene and Naphthothienobenzothiophene.

Previously it was demonstrated that triptycene end-capping can be used as a crystal engineering strategy to direct the packing of quinoxalinophenanthrophenazines (QPPs) towards cofacially stacked π dimers with large molecular overlap resulting in high charge transfer integrals. Remarkably, this packing motif was formed under different crystallization conditions and with a variety of derivatives bearing additional functional groups or aromatic substituents. Benzothienobenzothiophene (BTBT) and its derivatives are known as some of the best performing compounds for organic field-effect transistors. Here, the triptycene end-capping concept is introduced to this class of compounds and polymorphic crystal structures are investigated to evaluate the potential of triptycene end-caps as synthons for crystal engineering.

Di- and Tetracyano-Substituted Pyrene-Fused Pyrazaacenes: Aggregation in the Solid State.

Five di- and tetracyano-substituted pyrene-fused pyrazaacenes were synthesized and studied as potential electron acceptors in the solid state. Single crystals of all compounds were grown and the crystal packing studied by DFT calculations (transfer integrals and reorganization energies) to get insight into possible use for semiconducting charge transport.

Triptycene End-Capped Quinoxalinophenanthrophenazines (QPPs): Influence of Substituents and Conditions on Aggregation in the Solid State.

Triptycene end-capped quinoxalinophenanthrophenazine reveals a coplanar arrangement with a high overlap of the π planes. Four structurally related model compounds bearing electron-withdrawing or -donating groups were synthesized, and their optoelectronic properties were characterized by using cyclovoltammetry, absorption- and emission spectroscopy as well as theoretical calculations. The directional robustness of the triptycene end-capping of these compounds was tested by using single-crystal X-ray diffraction. The impact of solvents and crystallization conditions has also been investigated. In total, 17 single-crystal structures were obtained. Each structure was evaluated for its potential charge-transfer capability taking into account the overall molecular packing, solvent enclathration and the structural overlap of the π planes of adjacent molecules. For this purpose, charge-transfer integrals were also calculated for every π-stacked dimer.