Stabilizing Azaheptacenes.

The symmetrical 7,16-diaza-6,8,15,17-tetrakis(triisopropylsilylethynyl)heptacene was obtained by a Pd-catalyzed reaction of a 2,3-diamino-1,4-diethynylanthracene with a 2,3-dibromo-1,4-diethynyl anthracene. Positioning the TIPS-ethynyl groups adjacent to the central ring suppresses dimerization via [4+4] cycloadditions and Diels-Alder reactions; the middle pyrazine ring renders this species stable to oxidation. A single crystal structure was obtained, and thin film transistors with µn = 0.042 cm2 V-1 s-1 were produced. Transposition of the alkynyl groups into the 5,8,15,18-positions with a quinoxaline unit in the center of the heptacene decreases the stability, as does the introduction of two more nitrogen atoms into the 5,18-positions. The hydrocarbon 6,8,15,17-tetrakis(triisopropylsilylethynyl)heptacene is reasonably stable with a half-life of 25 h in solution. Four correctly placed TIPS-ethynyl groups protect heptacene cores.

Coordination Chemistry as a Universal Strategy for a Controlled Perovskite Crystallization.

The most efficient and stable perovskite solar cells (PSCs) are made from a complex mixture of precursors. Typically, to then form a thin film, an extreme oversaturation of the perovskite precursor is initiated to trigger nucleation sites, e.g., by vacuum, an airstream, or a so-called antisolvent. Unfortunately, most oversaturation triggers do not expel the lingering (and highly coordinating) dimethyl sulfoxide (DMSO), which is used as a precursor solvent, from the thin films; this detrimentally affects long-term stability. In this work, (the green) dimethyl sulfide (DMS) is introduced as a novel nucleation trigger for perovskite films combining, uniquely, high coordination and high vapor pressure. This gives DMS a universal scope: DMS replaces other solvents by coordinating more strongly and removes itself once the film formation is finished. To demonstrate this novel coordination chemistry approach, MAPbI3 PSCs are processed, typically dissolved in hard-to-remove (and green) DMSO achieving 21.6% efficiency, among the highest reported efficiencies for this system. To confirm the universality of the strategy, DMS is tested for FAPbI3 as another composition, which shows higher efficiency of 23.5% compared to 20.9% for a device fabricated with chlorobenzene. This work provides a universal strategy to control perovskite crystallization using coordination chemistry, heralding the revival of perovskite compositions with pure DMSO.