Reversible Emission Tunability from 2D‐Layered Perovskites with Conjugated Organic Cations

The structural flexibility of 2D‐layered halide perovskites provides unprecedented opportunities for tuning their optical properties. For example, lattice distortions facilitate white emission that stems from self‐trapped excitons or defects, and organic cations and halides determine structural stability and emission range. Herein, the optical properties of a set of single‐layer thiophene‐based 2D lead bromide platelets are investigated. Blue‐ and white‐emitting materials based on the choice of thiophene cation and HBr concentration in the synthesis and reversible white to blue color switching by sequential washing and precursor exposure of the fabricated samples are obtained. The photophysical and structural studies indicate that the key to color switching is the formation and suppression of self‐trapped excitons by the supply and removal of cations and halides in acetone. The range of emission color from these materials is extended to red by efficient Mn doping that leads to an additional strong emission peak centered at 620 nm. The findings stimulate the development of color‐tunable and switchable light emitters based on a single material