Transforming Ionene Polymers into Efficient Cathode Interlayers with Pendent Fullerenes

A new and highly efficient cathode interlayer material for organic photovoltaics (OPVs) was produced by integrating C₆₀ fullerene monomers into ionene polymers. The power of these novel “C₆₀‐ionenes” for interface modification enables the use of numerous high work‐function metals (e.g., silver, copper, and gold) as the cathode in efficient OPV devices. C₆₀‐ionene boosted power conversion efficiencies (PCEs) of solar cells, fabricated with silver cathodes, from 2.79 % to 10.51 % for devices with a fullerene acceptor in the active layer, and from 3.89 % to 11.04 % for devices with a non‐fullerene acceptor in the active layer, demonstrating the versatility of this interfacial layer. The introduction of fullerene moieties dramatically improved the conductivity of ionene polymers, affording devices with high efficiency by reducing charge accumulation at the cathode/active layer interface. The power of C₆₀‐ionene to improve electron injection and extraction between metal electrodes and organic semiconductors highlights its promise to overcome energy barriers at the hard‐soft materials interface to the benefit of organic electronics.     

Dependency of the Tunneling Decay Coefficient in Molecular Tunneling Junctions on the Topography of the Bottom Electrodes

A controversy in molecular electronics is the unexplained large spread in values of the tunneling decay coefficient β in tunneling junctions with self‐assembled monolayers of n‐alkanethiolates (SC_n). We show control of the β value over the range 0.4–1.0 n_C⁻¹ in junctions by changing the topography of the bottom electrodes that support the SAMs. Very low β values (0.4–0.5 n_C⁻¹) are obtained for rough surfaces with large areas of exposed grain boundaries, while β=1.0 n_C⁻¹ for smooth surfaces with small areas of exposed grain boundaries.     

Not Only Columns: High Hole Mobility in a Discotic Nematic Mesophase Formed by Metal‐Containing Porphyrin‐Core Dendrimers

We report a new family of multifunctional liquid‐crystalline porphyrin‐core dendrimers that have coumarin functional groups around the porphyrin core. Porphyrin metalation strongly affects the photophysical properties, and therefore Zn^II and Cu^II derivatives have also been prepared. All the synthesized dendrimers form a nematic discotic mesophase. Their high tendency for homeotropic alignment makes these dendrimers excellent candidates for device applications, owing to their easy processability, spontaneous alignment between electrodes, and self‐healing of defects because of their dynamic nature. The charge mobility values of these materials are the highest ever reported for a nematic discotic phase. Moreover, these values are similar to the highest values reported for ordered columnar mesophases, and this shows that a supramolecular organization in columns is not necessary to achieve high charge mobility.     

Charge Transport through Self‐Assembled Monolayers of Monoterpenoids

The nature of the processes at the origin of life that selected specific classes of molecules for broad incorporation into cells is controversial. Among those classes selected were polyisoprenoids and their derivatives. This paper tests the hypothesis that polyisoprenoids were early contributors to membranes in part because they (or their derivatives) could facilitate charge transport by quantum tunneling. It measures charge transport across self‐assembled monolayers (SAMs) of carboxyl‐terminated monoterpenoids (O₂C(C₉HX)) and alkanoates (O₂C(C₇HX)) with different degrees of unsaturation, supported on silver (Ag^TS) bottom electrodes, with Ga₂O₃/EGaIn top electrodes. Measurements of current density of SAMs of linear length‐matched hydrocarbons—both saturated and unsaturated—show that completely unsaturated molecules transport charge faster than those that are completely saturated by approximately a factor of ten. This increase in relative rates of charge transport correlates with the number of carbon–carbon double bonds, but not with the extent of conjugation. These results suggest that polyisoprenoids—even fully unsaturated—are not sufficiently good tunneling conductors for their conductivity to have favored them as building blocks in the prebiotic world.