Thermally Stable Charge Transport Materials for Vapor‐Phase Fabrication of Perovskite Devices

Perovskite light‐emitting diodes (PeLEDs) have attracted tremendous research interest in recent years. Cesium lead bromide's (CsPbBr3) high color purity, intrinsically high photoluminescence quantum yield, and tunable emission wavelength make it a strong candidate as an emitter for light‐emitting applications. Organic charge transport materials and their impact on the growth mode of the perovskite layer have a pivotal influence on the device performance. Herein, it is reported that hole transport layers (HTLs) with higher glass transition temperatures (Tg) are critical to facilitate the growth of crystalline perovskites and thus the color purity. Second phase regions with higher Pb density are observed in films growing on HTLs with inadequate lower Tg. A minimum 100 °C glass transition is found to be essential to grow cesium lead bromides with sharp emission peaks. In addition to high glass transition temperature, high ionization energy (>5.6 eV) is also found to be important to remove the HTL/perovskite injection barrier. The optimal device in this study is fabricated with 3,5‐di(9H‐carbazol‐9‐yl)tetraphenylsilane (SimCP2) as the HTL and the device shows a very sharp 19 nm full‐width at half‐maximum emission