Heterophase engineering enables efficient tin-based perovskite red light-emitting diodes for cardiac pulse detection

Tin (Sn)-based perovskite light-emitting diodes (LEDs), featuring environmental friendliness and low toxicity, have attracted growing interest as light sources for high-definition displays, medical and health monitoring applications. However, the widespread existing defects arising from the rapid crystallization and the undesirable oxidation of Sn²⁺ markedly limit the efficiency and brightness of current Sn-based perovskite LEDs. Herein, we develop an zero-dimensional (0D)–two-dimensional (2D) heterophasic transition strategy to promote the performance of PEA₂SnI₄ perovskite films. The results demonstrate that the formation of heterophase extends the processing time window of perovskites, thereby enabling effective modulation and optimization of films crystallization process by regulating initial nucleation. Finally, the fabricated device based on the optimized PEA₂SnI₄ films achieves a maximum external quantum efficiency (EQE) of 9% and a luminance of 1253.3 cd·m⁻², representing one of the highest performances reported to date for PEA₂SnI₄-based perovskite LEDs. Furthermore, the fabricated device was successfully employed as light sources for human cardiac pulse detection, achieving performances comparable to that of commercial detectors, representing the first demonstration of such functionality in lead-free perovskite systems.