Triplet excitons (TE), bound electron-hole pairs with unity spin and long lifetime, form the basis for exploitation in applications including singlet oxygen generation, photodynamic therapy, and photochemical upconversion. As a result, an emerging theme in the realm of nanostructured inorganic semiconductors is the extraction of their transiently stored potential in the form of molecular triplet excited states. In some instances, the efficiency of the triplet energy transfer process approaches unity, leading to generation of surface-bound triplets with lifetimes on the millisecond time scale. These observations are mostly limited to molecular or reduced-dimensional structures, and most typically are pursued in solution phase. While organic-inorganic perovskites have attracted substantial attention for application to optoelectronics, the generation of TEs from the broad perovskite family (i.e., both 3D and lower-dimensional frameworks) remains largely unexplored. In the present work, efficient TE generation on picosecond time scales in a 2D perovskite (CH3NH3)2Pb(SCN)2I2 is demonstrated using static and transient spectroscopic techniques.
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