Yellow light-emitting diodes (LEDs) as soft light have attracted abundant attention in lithography room, museum and art gallery. However, the development of efficient yellow LEDs lags behind green and blue LEDs, and the available perovskites yellow LEDs suffer from the instability. Herein, a pressure-assisted cooling method is proposed to grow lead-free CsCu₂I₃ single crystals, which possess uniform surface morphology and enhanced photoluminescence quantum yield (PLQY) stability, with only 10% PLQY losses after being stored in air after 5000 ​h. Then, the single crystals used for yellow LEDs without encapsulation exhibit a decent Correlated Color Temperature (CCT) of 4290 ​K, a Commission Internationale de l'Eclairage (CIE) coordinate of (0.38, 0.41), and an excellent 570-h operating stability under heating temperature of 100 ​℃. Finally, the yellow LEDs facilitate the application in wireless visible light communication (VLC), which show a −3 dB bandwidth of 21.5 ​MHz and a high achievable data rate of 219.2 Mbps by using orthogonal frequency division multiplexing (OFDM) modulation with adaptive bit loading. The present work not only promotes the development of lead-free single crystals, but also inspires the potential of CsCu₂I₃ in the field of yellow illumination and wireless VLC.

The perovskite layer, electron transport layer (ETL) and their interface are closely associated with carrier transport and extraction, which possess a pronounced effect on current density. Consequently, the dissatisfactory electric properties of functional layers pose a serious challenge for maximizing the thermodynamic potential of current density of perovskite solar cells (PSCs). Herein, we report an ion diffusion-induced double layer doping strategy for efficient and stable PSCs, where LiOH is directly added into SnO₂ colloidal dispersion solution. It is uncovered that a small amount of Li⁺ ions remain in the ETL and doped SnO₂ while a large amount of Li⁺ ions diffuse to SnO₂/perovskite interface and into perovskite layer and gradient concentration distribution is spontaneously formed. The Li⁺ ion doping endows both perovskite and SnO₂ layers improved electric properties, which contributes to facilitated carrier transport and extraction. Moreover, the crystallinity and grain size of perovskite films are enhanced after doping. The doped device delivers a higher power conversion efficiency (PCE) of 21.31% together with improved ambient stability in comparison with the control device (PCE = 19.26%). This work demonstrates a simple and effective ion diffusion-induced double layer by chemical doping strategy to advance the development of perovskite photovoltaics.