ACS Energy Letters

Colloidal CsPbX3 (X = Cl, Br, I) Nanocrystals 2.0: Zwitterionic Capping Ligands for Improved Durability and Stability

Colloidal lead halide perovskite nanocrystals (NCs) have recently emerged as versatile photonic sources. Their processing and optoelectronic applications are hampered by the loss of colloidal stability and structural integrity due to the facile desorption of surface capping molecules during isolation and purification. To address this issue, herein, we propose a new ligand capping strategy utilizing common and inexpensive long-chain zwitterionic molecules such as 3-(N,N-dimethyloctadecylammonio)propanesulfonate, resulting in much improved chemical durability. In particular, this class of ligands allows for the isolation of clean NCs with high photoluminescence quantum yields (PL QYs) of above 90% after four rounds of precipitation/redispersion along with much higher overall reaction yields of uniform and colloidal dispersible NCs. Densely packed films of these NCs exhibit high PL QY values and effective charge transport. Consequently, they exhibit photoconductivity and low thresholds for amplified spontaneous emission of 2 μJ cm–2 under femtosecond optical excitation and are suited for efficient light-emitting diodes.

Phase-Stable Red-Emitting CsPbI3 Nanocrystals: Successes and Challenges

The semiconducting bulk α-cubic CsPbI3 phase is stable at high temperature. However, recent developments concluded that in nanodimensions this phase can also be stable even at room temperature. The unique feature of these α-CsPbI3 nanocrystals is their low-energy red color emission, which remained an essential part for the perovskite family of nanocrystals to cover the entire visible spectrum. Even though these were reported to be stable at room temperature, it is only under certain conditions. These are mostly phase-sensitive, and under ambient conditions, the α phase is transformed to a nonemitting phase. Hence, the phase stability in these nanocrystals remained one of the major challenges in current research. In this Perspective, the origin of phase instability, observations of change in optical properties along with phase transformation under different environmental conditions, insights of possible modulations in A, B, and X sites of the perovskites, precaution in the purification process, and the ligand shell chemistry adopted during and postsynthesis for obtaining the stability of these CsPbI3 nanocrystals were systematically analyzed and reported. In addition, different possible aspects of future research for retaining the phase stability are also discussed.

Long-Lasting Ni-Rich NCMA Cathodes via Simultaneous Microstructural Refinement and Surface Modification

Li[Ni1–x–y–zCoxMnyAlz]O2 (NCMA) cathodes have attracted public attention owing to their improved durability by leveraging the advantages of NCM and NCA cathodes. As the Ni content approaches 90%, however, it is challenging to realize high-energy Ni-rich NCMA cathodes without sacrificing durability. Herein, we improve the cycling stability of a Ni-rich Li[Ni0.93Co0.03Mn0.03Al0.01]O2 (NCMA93) cathode using a combination strategy involving microstructural refinement and surface modification. The F-coating-induced protective layer of the F-coated, Sb-doped NCMA93 cathode combined with its engineered microstructure enables the formation of a robust cathode–electrolyte interphase (CEI) layer on the cathode surface, which suppresses surface degradation to afford a long battery life. However, the F coating alone does not significantly improve the cycling stability of cathode because it suffers severe microcracking during cycling owing to its suboptimal microstructure. To realize a cathode with a long lifespan, a robust CEI layer should be generated and maintained on the cathode without severe microcracking.

Issue Editorial Masthead

Narrow-Bandgap Halide Perovskite Cs4CuSb2Cl12 with Full-Spectrum Photothermal Conversion

Light-to-heat conversion represents one of the most promising pathways to utilize full-spectrum solar energy. The key for boosting the photothermal conversion in semiconductor-based light absorbers relies on narrowing the bandgap for harvesting wide-range sunlight and localizing thermal energy via decreasing heat loss. Here, we demonstrate the first example of using a halide perovskite, Cs4CuSb2Cl12, as the photothermal material for efficient solar-to-heat conversion, with an intrinsic narrow bandgap and ultralow thermal conductivity. Full-spectrum (200–2500 nm) absorption and solar-thermal conversion efficiency up to 93.4% are achieved. The photothermal property enables a low-temperature and rapid hydrogen production from ammonia borane, with 2.0 equiv of hydrogen released, and a photothermal activation efficiency of 12.2% is realized, without any extra energy input. This high photothermal performance not only provides a potential for an energy-efficient on-board hydrogen supply for fuel cells but also opens up a new field for halide perovskites utilized as photothermal convertors.

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