Recent Progress on Crystalline Organic Light‐Emitting Diodes Based on Weak‐Epitaxy‐Growth 2FPPICz Polycrystalline Thin Films

Crystalline organic semiconductor‐based organic light‐emitting diodes (C‐OLEDs) have drawn significant attention in the organic optoelectronics field in the past years, owing to their highly ordered molecular arrangements and excellent carrier transport performance. Among them, crystalline host matrix (CHM) materials represented by 2‐(4‐(9H‐carbazol‐9‐yl)phenyl)‐1‐(3,5‐difluorophenyl)‐1H‐phenanthro[9,10‐d]imidazole (2FPPICz) have become ideal hosts for constructing high‐performance C‐OLEDs due to evident advantages, such as their unique weak epitaxial growth (WEG) characteristics (enabling large‐area uniform film formation), wide bandgap (2.23–5.53 eV), and precisely controllable host–guest molecular arrangements. This review focuses on 2FPPICz crystalline host matrix‐based C‐OLED systems and systematically discusses their recent progress. Their physical structure designs of the light‐emitting layer are specifically highlighted, including i) doping, ii) solid‐solution, and iii) nanoaggregate structures. Additionally, this review explores the unique advantages of C‐OLEDs and discusses their current challenges and future prospects. It is believed that this review will provide valuable references for understanding the luminescence mechanisms of C‐OLEDs. It will also help in formulating strategies to develop high‐performance OLEDs.