Plasticizer Design Principle of “Like Dissolves Like”: Semiconductor Fluid Plasticized Stretchable Fully π‐Conjugated Polymers Films for Uniform Large‐Area and Flexible Deep‐Blue Polymer Light‐Emitting Diodes

Abstract Physical blending of fully π‐conjugated polymers (FπCPs) is an effective strategy to achieve intrinsically stretchable films for the fabrication of flexible optoelectronic devices, but easily causes phase separation, nonuniform morphology and uncontrollable photo‐electronic processing. This may cause low efficiency, unstable and nonuniform emission, and poor color purity, which are undesirable for deep‐blue flexible polymer light‐emitting diodes (FPLEDs). Herein, a “Like Dissolves Like” design principle to prepare semiconductor fluid plasticizers (SFPs) is established and intrinsically stretchable FπCPs films via external plasticization for high‐performance deep‐blue FPLEDs are developed. Three fundamental requirements are proposed, “similar conjugated skeleton, similar molecular polarity, and similar electronic structures,” to prepare model‐matched nonpolar M1 and polar M2 plasticizers for poly(9,9‐dioctylfluorene) (PFO). Large‐area plasticized PFO films exhibit an efficient, narrowband, and stable ultra‐deep‐blue electroluminescence (FWHM < 40 nm, CIE: 0.12, 0.04), uniform morphology, and excellent intrinsic stretchability (fracture strain >20% and crack‐onset strain >120%). Efficient and uniform deep‐blue FPLEDs based on stretchable PFO films are fabricated with a high brightness of ≈3000 cd cm −2 . Finally, blended PFO films exhibit outstanding stretch‐deformation cycling stability of their deep‐blue electroluminescent behavior, confirming the effectiveness of the “Like Dissolves Like” principle to design matched SFPs for stretchable FπCP films in flexible electronics.