Phase‐Purified Ruddlesden–Popper Perovskites Vertically Oriented in Block Copolymer Nanostructures for Environmentally Stable Light Conversion and Charge Trapping

Abstract 2D Ruddlesden–Popper perovskites (RPPs) with 2D layer‐tunable optoelectronic properties suffer from randomly oriented multiple phases. Herein, an efficient method for developing RPP films with controlled phase purity and crystal orientation via a one‐step synthesis of RPPs in a self‐assembled block copolymer (BCP) film is demonstrated. RPP crystals with a target phase are preferentially embedded in the poly(ethylene oxide) domains of a polystyrene‐block‐poly(ethylene oxide) nanostructured film. Interestingly, rapid self‐assembly with the BCP results in phase‐purified n = 2 and 3 targeted RPPs with a target phase percentage two and four times higher, respectively, than that of pristine RPP. Furthermore, RPP crystals synthesized within BCP are preferentially oriented with their b‐axis parallel to the surface normal. The photoluminescence of the composite film is significantly enhanced, allowing environmentally stable ultraviolet‐to‐blue color conversion. Moreover, semiconducting RPP crystals nanopatterned in the BCP are successfully used as charge‐trapping floating nanogates, resulting in a non‐volatile field‐effect transistor memory.