Organic Light–Emitting Diodes In article number 2310268, Heonsu Jeon, Jeong Hyun Kwon, and co-workers customize a multifunctional hazy polymer substrate for extreme environments using a simple ion-beam treatment and functional barrier film to realize highly reliable next-generation displays. By using the developed multifunctional substrate, highly efficient and reliable wearable organic light-emitting diodes applicable in various fields are realized by improving their efficiency and environmental reliability.