Halide perovskites, including CsPbX (X = Cl, Br, I), have gained much attention in the field of optoelectronics. However, the toxicity of Pb and the low photoluminescence quantum yield (PLQY) of these perovskites hamper their use. In this work, new halide materials that meet the requirements of: (i) nontoxicity, (ii) high PLQY, and (iii) ease of fabrication of thin films via the solution process are explored. In particular, copper(I) halide compounds with low-dimensional electronic structures are considered. Cs Cu I has a 0D photoactive site and exhibits blue emission (≈445 nm) with very high PLQYs of ≈90 and ≈60% for single crystals and thin films, respectively. The large exciton binding energy of ≈490 meV explains well the 0D electronic nature of Cs Cu I . Blue electroluminescence of Pb-free halides is demonstrated using solution-derived Cs Cu I thin films.

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Low-dimensional lead-free luminescent halides have emerged as highly promising phosphors for white-light emission. Recently, we reported a broadband blue-emitting copper(I) iodide-based material, Cs3Cu2I5, with a high photoluminescence quantum yield (PLQY) (∼90%) and a zero-dimensional nature, providing significant dimensionality for the photoactive site. However, this material is insufficient as a white-light emitter owing to the deficient yellow emission. In this paper, we report a novel yellow luminescent phosphor, CsCu2I3, with a 1D structure for the photoactive site. This material exhibits a broadband emission centered at ∼560 nm with a PLQY of ∼8%. We demonstrate a thin film with white-light emission that can be fabricated using one-step spin-coating of a mixed precursor solution of 1D CsCu2I3 (yellow) and 0D Cs3Cu2I5 (blue).

Metal halide perovskites (MHPs) are plausible candidates for practical p-type semiconductors. However, in thin film transistor (TFT) applications, both 2D PEA 2 SnI 4 and 3D FASnI 3 MHPs have different drawbacks. In 2D MHP, the TFT mobility is seriously reduced by grain-boundary issues, whereas 3D MHP has an uncontrollably high hole density, which results in quite a large threshold voltage (V th ). To overcome these problems, a new concept based on a 2D-3D core-shell structure is herein proposed. In the proposed structure, a 3D MHP core is fully isolated by a 2D MHP, providing two desirable effects as follows. (i) V th can be independently controlled by the 2D component, and (ii) the grain-boundary resistance is significantly improved by the 2D/3D interface. Moreover, SnF 2 additives are used, and they facilitate the formation of the 2D/3D core-shell structure. Consequently, a high-performance p-type Sn-based MHP TFT with a field-effect mobility of ≈25 cm 2 V −1 s −1 is obtained. The voltage gain of a complementary metal oxide semiconductor (CMOS) inverter comprising an n-channel InGaZnO x TFT and a p-channel Sn-MHP TFT is ≈200 V/V at V DD = 20 V. Overall, the proposed 2D/3D core-shell structure is expected to provide a new route for obtaining high-performance MHP TFTs.