The mixed caesium and formamidinium lead triiodide perovskite system (Cs1-xFAxPbI3) in the form of quantum dots (QDs) offers a new pathway towards stable perovskite-based photovoltaics and optoelectronics. However, it remains challenging to synthesize such multinary QDs with desirable properties for high-performance QD solar cells (QDSCs). Here we report an effective ligand-assisted cation exchange strategy that enables controllable synthesis of Cs1-xFAxPbI3 QDs across the whole composition range (x: 0-1), which is inaccessible in large-grain polycrystalline thin films. The surface ligands play a key role in driving the cross-exchange of cations for the rapid formation of Cs1-xFAxPbI3 QDs with suppressed defect density. The hero Cs0.5FA0.5PbI3 QDSC achieves a certified record power conversion efficiency (PCE) of 16.6% with negligible hysteresis. We further demonstrate that QD devices exhibit substantially enhanced photostability compared to their thin film counterparts because of the suppressed phase segregation, retaining 94% of the original PCE under continuous 1-sun illumination for 600 hours.

Lead halide perovskites have witnessed significant progress in low-cost and high-efficiency photovoltaics, with a rapid increase in photovoltaic efficiencies from 3.8% to a certified record of 25.2% in the past decade. [1-4] However, the viability and practical scale-up implementation are limited by the stability and toxicity of the lead halide perovskites. [5,6] To circumvent these two

The phenethylammonium cation significantly promotes the formation of fully-covered thin-films of hybrid bismuth organohalides with low surface roughness and excellent stability.

Quantum dots (QDs) of formamidinium lead triiodide (FAPbI3) perovskite hold great potential, outperforming their inorganic counterparts in terms of phase stability and carrier lifetime, for high‐performance solar cells. However, the highly dynamic nature of FAPbI3 QDs, which mainly originates from the proton exchange between oleic acid and oleylamine (OAm) surface ligands, is a key hurdle that impedes the fabrication of high‐efficiency solar cells. To tackle such an issue, here, protonated‐OAm in situ to strengthen the ligand binding at the surface of FAPbI3 QDs, which can effectively suppress the defect formation during QD synthesis and purification processes is selectively introduced. In addition, by forming a halide‐rich surface environment, the ligand density in a broader range for FAPbI3 QDs without compromising their structural integrity, which significantly improves their optoelectronic properties can be modulated. As a result, the power conversion efficiency of FAPbI3 QD solar cells (QDSCs) is enhanced from 7.4% to 13.8%, a record for FAPbI3 QDSCs. Furthermore, the suppressed proton exchange and reduced surface defects in FAPbI3 QDs also enhance the stability of QDSCs, which retain 80% of the initial efficiency upon exposure to ambient air for 3000 hours.

Perovskite solar cells (PSCs) have witnessed an unprecedentedly rapid development, especially in terms of power conversion efficiency (PCE). However, the solution-processed perovskite films inevitably possess numerous crystallographic defects (e.g., halide vacancies), which has been shown to incur non-radiative charge recombination and ion migration, thus limiting the enhancement of the PCE and stability of PSCs. Here, a novel dual metal (i.e., divalent and monovalent metal ions) modification strategy is reported for simultaneously reducing the defects, immobilizing the halide anions, and preventing ion loss from perovskite during post-annealing process. Accordingly, this strategy significantly reduces non-radiative recombination, enhancing the PCE by ≈12% and mitigating the current density-voltage (J-V) hysteresis effect in resultant devices compared to undoped counterparts. As a result, a champion PCE exceeding 22% and a high open-circuit voltage (V oc ) of 1.16 V is obtained for dual metal ions-modified PSCs. The optimized devices also exhibit extended lifespan upon the dual metal treatment. The study provides a new defect engineering strategy toward more efficient and stable perovskite photovoltaics.

This manuscript describes the design and synthesis of Ru catalysts that feature only a single stereogenic element, yet this minimal chirality resource is demonstrated to be competent for effecting high levels of stereoinduction in the asymmetric transfer hydrogenation over a broad range of ketone substrates, including those that are not accommodated by known catalyst systems. The single stereogenic center of the (1-pyridine-2-yl)­methanamine) is the only point-chirality in the catalysts, which simplifies this catalyst system relative to existing literature protocols.

The borrowing-hydrogen (or hydrogen autotransfer) process, where the catalyst dehydrogenates a substrate and formally transfers the H atom to an unsaturated intermediate, is an atom-efficient and environmentally benign transformation. Described here is an example of an asymmetric borrowing-hydrogen cascade for the formal anti-Markovnikov hydroamination of allyl alcohols to synthesize optically enriched γ-secondary amino alcohols. By exploiting the Ru-(S)-i PrPyme catalyst with minimal stereogenicity, a cascade process including dehydrogenation, conjugate addition, and asymmetric reduction was developed. The mild conditions, functional group tolerance, and broad substrate scope (54 examples) demonstrate the synthetic practicality of the catalytic system.

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