The performance of perovskite solar cells with inverted polarity ( p-i-n ) is still limited by recombination at their electron extraction interface, which also lowers the power conversion efficiency (PCE) of p-i-n perovskite-silicon tandem solar cells. A ~1 nm thick MgF x interlayer at the perovskite/C 60 interface through thermal evaporation favorably adjusts the surface energy of the perovskite layer, facilitating efficient electron extraction, and displaces C 60 from the perovskite surface to mitigate nonradiative recombination. These effects enable a champion V oc of 1.92 volts, an improved fill factor of 80.7%, and an independently certified stabilized PCE of 29.3% for a ~1 cm 2 monolithic perovskite-silicon tandem solar cell. The tandem retained ~95% of its initial performance following damp-heat testing (85 Celsius at 85% relative humidity) for > 1000 hours.

Mechanistic studies involving synergistic experiment and theory were performed on the perfectly alternating copolymerization of 1-butene oxide and carbic anhydride using a (salph)AlCl/[PPN]Cl catalytic pair. These studies showed a first-order dependence of the polymerization rate on the epoxide, a zero-order dependence on the cyclic anhydride, and a first-order dependence on the catalyst only if the two members of the catalytic pair are treated as a single unit. Studies of model complexes showed that a mixed alkoxide/carboxylate aluminum intermediate preferentially opens cyclic anhydride over epoxide. In addition, ring-opening of epoxide by an intermediate comprising multiple carboxylates was found to be rate-determining. On the basis of the experimental results and analysis by DFT calculations, a mechanism involving two catalytic cycles is proposed wherein the alternating copolymerization proceeds via intermediates that have carboxylate ligation in common, and a secondary cycle involving a bis-alkoxide species is avoided, thus explaining the lack of side reactions until the polymerization is complete.

No abstract

Site selectivity represents a key challenge for non-directed C−H functionalization, even when the C−H bond is intrinsically reactive. Here, we report a copper-catalyzed method for benzylic C−H azidation of diverse molecules. Experimental and density functional theory studies suggest the benzyl radical reacts with a Cu II -azide species via a radical-polar crossover pathway. Comparison of this method with other C−H azidation methods highlights its unique site selectivity, and conversions of the benzyl azide products into amine, triazole, tetrazole, and pyrrole functional groups highlight the broad utility of this method for target molecule synthesis and medicinal chemistry.

In a possibly biomimetic fashion, formally copper­(III)–oxygen complexes LCu­(III)–OH (1) and LCu­(III)–OOCm (2) (L2– = N,N′-bis­(2,6-diisopropylphenyl)-2,6-pyridinedicarboxamide, Cm = α,α-dimethylbenzyl) have been shown to activate X–H bonds (X = C, O). Herein, we demonstrate similar X–H bond activation by a formally Cu­(III) complex supported by the same dicarboxamido ligand, LCu­(III)–O2CAr1 (3, Ar1 = meta-chlorophenyl), and we compare its reactivity to that of 1 and 2. Kinetic measurements revealed a second order reaction with distinct differences in the rates: 1 reacts the fastest in the presence of O–H or C–H based substrates, followed by 3, which is followed by (unreactive) 2. The difference in reactivity is attributed to both a varying oxidizing ability of the studied complexes and to a variation in X–H bond functionalization mechanisms, which in these cases are characterized as either a hydrogen-atom transfer (HAT) or a concerted proton-coupled electron transfer (cPCET). Select theoretical tools have been employed to distinguish these two cases, both of which generally focus on whether the electron (e–) and proton (H+) travel “together” as a true H atom, (HAT), or whether the H+ and e– are transferred in concert, but travel between different donor/acceptor centers (cPCET). In this work, we reveal that both mechanisms are active for X–H bond activation by 1–3, with interesting variations as a function of substrate and copper functionality.