Solution-processed hybrid organic−inorganic perovskites (HOIPs) from organoammonium halide and lead halide precursors form efficacious active layers for photovoltaics, light-emitting diodes, and flexible electronics. Though solvent−solute coordination plays a critical role in HOIP crystallization, the influence of solvent choice on such interactions is poorly understood. We demonstrate Gutmann's donor number, D N , as a parameter that indicates the coordinating ability of the processing solvent with the Pb 2+ center of the lead halide precursor. Low D N solvents interact weakly with the Pb 2+ center, favoring instead complexation between Pb 2+ and iodide and subsequent crystallization of perovskite. High D N solvents coordinate more strongly with the Pb 2+ center, which in turn inhibits iodide coordination and stalls perovskite crystallization. Varying the concentration of high-D N additives in precursor solutions tunes the strength of lead− solvent interactions, allowing finer control over the crystallization and the resulting morphology of HOIP active layers.

The chemical looping reforming (CLR) process, which utilizes a transition metal oxide based redox catalyst to partially oxidize methane to syngas, represents a potentially efficient approach for methane valorization. The CLR process inherently avoids costly cryogenic air separation by replacing gaseous oxygen with regenerable ionic oxygen (O(2-)) from the catalyst lattice. Our recent studies show that an Fe2O3@La0.8Sr0.2FeO3-δ core-shell redox catalyst is effective for CLR, as it combines the selectivity of an LSF shell with the oxygen capacity of an iron oxide core. The reaction between methane and the catalyst is also found to be highly dynamic, resulting from changes in lattice oxygen availability and surface properties. In this study, a transient pulse injection approach is used to investigate the mechanisms of methane partial oxidation over the Fe2O3@LSF redox catalyst. As confirmed by isotope exchange, the catalyst undergoes transitions between reaction "regions" with markedly different mechanisms. While oxygen evolution maintains a modified Mars-van Krevelen mechanism throughout the reaction with O(2-) conduction being the rate limiting step, the mechanism of methane conversion changes from an Eley-Rideal type in the first reaction region to a Langmuir-Hinshelwood-like mechanism in the third region. Availability of surface oxygen controls the reduction scheme of the catalyst and the underlying reaction mechanism.

Strong coordination between Lewis-basic processing additives and the Lewis-acidic lead halide in hybrid organic− inorganic perovskite (HOIP) precursor solutions is required to solubilize the lead halide, and subsequently access the appropriate crystallization kinetics and attain the desired morphology of perovskite active layers. While oxygen-donor solvents and additives, such as dimethylformamide and dimethyl sulfoxide, are widely used for perovskite processing, we demonstrate that "soft" sulfur-donor solvents exhibit stronger coordination to the "borderline soft" Lewis acid Pb 2+ center of PbI 2 relative to "hard" O-donor solvents in the precursor solution. The stronger coordination of Sdonor solvents compared to O-donor solvents to Pb 2+ implies that such compounds can be useful additives to HOIP precursor solutions. Density-functional calculations of the enthalpy change resulting from the coordination of solvents to Pb 2+ provide direct numerical comparison of the strength of O-donor and S-donor coordination with Pb 2+ and expands the library of candidate S-donor compounds. Our results provide a roadmap for processing additive selection and expand the previously limited choice of perovskite processing additives to include strongly coordinating S-donor compounds.

Typical lead‐based perovskites solar cells show an onset of photogeneration around 800 nm, leaving plenty of spectral loss in the near‐infrared (NIR). Extending light absorption beyond 800 nm into the NIR should increase photocurrent generation and further improve photovoltaic efficiency of perovskite solar cells (PSCs). Here, a simple and facile approach is reported to incorporate a NIR‐chromophore that is also a Lewis‐base into perovskite absorbers to broaden their photoresponse and increase their photovoltaic efficiency. Compared with pristine PSCs without such an organic chromophore, these solar cells generate photocurrent in the NIR beyond the band edge of the perovskite active layer alone. Given the Lewis‐basic nature of the organic semiconductor, its addition to the photoactive layer also effectively passivates perovskite defects. These films thus exhibit significantly reduced trap densities, enhanced hole and electron mobilities, and suppressed illumination‐induced ion migration. As a consequence, perovskite solar cells with organic chromophore exhibit an enhanced efficiency of 21.6%, and substantively improved operational stability under continuous one‐sun illumination. The results demonstrate the potential generalizability of directly incorporating a multifunctional organic semiconductor that both extends light absorption and passivates surface traps in perovskite active layers to yield highly efficient and stable NIR‐harvesting PSCs.

Proton transfer from methylammonium (CH 3 NH 3 + ) to dimethylsulfoxide (DMSO), a common Lewis-base solvent, initiates the production of ammonium (NH 4 + ) and dimethylammonium ([CH 3 ] 2 NH 2 + ). We propose two parallel reaction pathways initiated by this proton transfer. Using DMSO-d 6 to elucidate reaction schemes, we demonstrate that protonation is followed either by methyl group transfer between the resulting CH 3 NH 2 and residual CH 3 NH 3 + , or by transmethylation to CH 3 NH 2 from DMSOH + . The former reaction yields NH 4 + and (CH 3 ) 2 NH 2 + and is the dominant pathway at processing relevant temperatures; the latter yields (CH 3 ) 2 NH 2 + in addition to methylsulfonic acid and dimethylsulfide. In the preparation of hybrid organic−inorganic perovskite (HOIP) thin films for photovoltaic applications, the substitution of CH 3 NH 3 + with NH 4 + and (CH 3 ) 2 NH 2 + in the HOIP crystal results in deviations from the tetragonal structure expected of phase-pure CH 3 NH 3 PbI 3 , with a deleterious effect on the absorptivity of the resulting films. These results emphasize the importance of elucidating the under-appreciated precursor/solvent reactivity, the products of which, when incorporated into the solid state, can have profound effects on HOIP composition and structure, with a commensurate impact on macroscopic properties and device performance.