[en] Halide perovskites are rising as promising luminescent materials for display applications for their sharp emission peaks and high luminescence quantum yield. However, the heavy metal character of lead is one concern that shadows its application. In this work, monolayer Ruddlesden–Popper 2D structural tin perovskite (PEA)₂SnI₄ (PEA = C₈H₉NH₃ ⁺) is explored for a pure red color light emitting diode (LED). The manipulation of crystal growth kinetics enables the formation of highly ordered nanoplates, bringing high luminescence yield approaching 10% with an emission peak at 630 nm. Meanwhile, the highly oriented and ordered nanoplates structure allows effective carrier injection. The LED shows a low turn on voltage of 2.2 V, an external quantum efficiency of 0.52% and a max luminance of 355 cd m⁻². The luminescence quantum yield is comparable to the best performing device based on lead perovskites in the pure red emission region. This work provides a strategy to explore 2D structures for efficient macroscale LEDs. (paper)

[en] Lead halide perovskites with mixed cations/anions often suffer from phase segregation, which is detrimental to device efficiency and their long-term stability. During perovskite film growth, the gel stage (in between liquid and crystalline) correlates to phase segregation, which has been rarely explored. Herein, cation diffusion kinetics are systematically investigated at the gel stage to develop a diffusion model obeying Fick's second law. Taking 2D layered perovskite as an example, theoretical and experimental results reveal the impact of diffusion coefficient, temperature, and gel duration on the film growth and phase formation. A homogenous 2D perovskite thin film was then fabricated without significant phase segregation. This in-depth understanding of gel stage and relevant cation diffusion kinetics would further guide the design and processing of halide perovskites with mixed composition to meet requirements for optoelectronic applications. (© 2020 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)