Post‐synthesis anion exchange of all‐inorganic cesium lead halide perovskite nanocrystals (CsPbX3 NCs, where X=Cl, Br, and/or I) provides a rapid and simple means of tuning their band gap and photoluminescence emission wavelengths. Here we report color‐shifting of CsPbX3 nanocrystals induced by a macromolecular source of halide ions, specifically using polystyrene with ammonium halides as pendent groups. This strategy for introducing new halides to the perovskite nanocrystals gave access to perovskite‐polymer hybrid materials as solutions, thin films, or free‐flowing powders. Spectroscopic measurements of the halide‐exchanged nanocrystal products revealed high photoluminescence quantum yields across the visible spectrum, with exchange kinetics that were tunable based on the solution environment, suggesting an aggregation‐inhibited exchange process that affords access to multi‐colored solutions and films.

Traditional hot injection methods for the preparation of cesium lead halide perovskite nanocrystals (CsPbX 3 PNCs, where X=Cl, Br, or I) rely on small molecule surfactants to produce PNCs with cube, plate, or rod-like morphologies.Here, we describe a new method whereby zwitterionic block copolymers are employed as macromolecular ligands in PNC synthesis, affording PNCs with excellent colloidal stability, high photoluminescence quantum yield, and in some cases distinctly non-cubic shapes. The block copolymers used in this study -composed of a poly(n-butyl methacrylate) hydrophobic block and zwitterionic methacrylate hydrophilic blocks -dissolve in useful solvents for PNC growth despite containing large mole percentages of zwitterionic groups. PNCs prepared with block copolymer ligands were found to disperse and retain their fluorescence in a range of polar organic solvents and were amenable to direct integration into optically transparent nanocomposite thin films with high PNC content.

Organic solar cells (OSCs) and perovskite solar cells (PVSCs) are promising candidates for next-generation thin film photovoltaic technologies. The integration of OSCs with PVSCs in tandem devices is now attracting significant attention due to their similar fabrication procedures and the potential to afford a higher device performance. Here, a thickness-insensitive and solvent-resistant interconnecting layer is developed to efficiently connect perovskite and organic subcells with low contact resistance. The resultant perovskite-organic tandem devices maintain high efficiencies over a wide thickness range of the interconnecting layer, from ∼20 nm to ∼50 nm, providing an easily fabricated, solvent-resistant platform to integrate perovskite and organic active layers with low-temperature solution processing techniques. The tandem devices containing an ultrathin PVSC and a typical non-fullerene OSC give a maximum efficiency of 19.2%, which is much higher than those of the single-junction devices. Moreover, highly reproducible 1 cm2 perovskite-organic tandem devices are achieved using the thickness-insensitive and solvent-resistant interconnecting layer, and an efficiency of 17.8% is realized. These 1 cm2 tandem solar cells are used successfully in solar-to-hydrogen systems to afford a solar-to-fuel conversion efficiency of 11.2%. Overall, these advances represent significant progress in the design of ultrathin and facile solution processed perovskite-organic tandem solar cells.

Post‐synthesis anion exchange of all‐inorganic cesium lead halide perovskite nanocrystals (CsPbX3 NCs, where X=Cl, Br, and/or I) provides a rapid and simple means of tuning their band gap and photoluminescence emission wavelengths. Here we report color‐shifting of CsPbX3 nanocrystals induced by a macromolecular source of halide ions, specifically using polystyrene with ammonium halides as pendent groups. This strategy for introducing new halides to the perovskite nanocrystals gave access to perovskite‐polymer hybrid materials as solutions, thin films, or free‐flowing powders. Spectroscopic measurements of the halide‐exchanged nanocrystal products revealed high photoluminescence quantum yields across the visible spectrum, with exchange kinetics that were tunable based on the solution environment, suggesting an aggregation‐inhibited exchange process that affords access to multi‐colored solutions and films.

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