Dynamic bandgap modulation in CsPbBr perovskite nanocrystals through reversible ammonia intercalation.

Modulation of the electronic states of a semiconductor is an intriguing area of research because of its interesting applications. In general, physical methods are used to reversibly manipulate the bandgap of semiconductors. Herein, we have used a simple molecule, ammonia, and allowed it to intercalate inside the crystal lattice of CsPbBr perovskites to alter the band positions. The molecular intercalation of ammonia induces strain in the crystal structure of perovskite, which widens the bandgap. Ammonia intercalation results in fall-off of the visible absorption and emission of the CsPbBr perovskites and a new absorption emerges in the ultraviolet region. Interestingly, with time, the deintercalation takes place, as a result of the population in the antibonding orbitals formed due to the mixing of s orbital of the Pb and p orbital of N in the intercalated NH. The deintercalation of gaseous ammonia results in the narrowing of the bandgap which results in the regaining of the visible absorption. Together with the density functional theory calculations, herein, we demonstrate the reversible bandgap modulation in CsPbBr perovskite nanocrystals. Aspects discussed here can give directions to develop newer methodologies to tune the band positions of semiconductors by the intercalation of the right molecules inside their crystal lattice.