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Modulation of Electronic States of Hybrid Lead Halide Perovskite Embedded in Organic Matrix

The modulation of electronic states of MAPbX3 perovskite nano-crystals (PNCs) (MA =CH3NH3+ & X = Brand I- ) as a function of crystallite size in organic semiconductor matrix forming a type-I hetero-structures with the bulk perovskites. Organic semiconductor molecules [(4,4'-bis[9-dicarbazolyl]-2,2'-biphenyl (CBP) & bathocuproine (BCP)] precursors have been mixed in different volumetric ratio with MAPbX3 perovskite precursors to prepare the thin-film. This results into an easy growth of MAPbX3 PNCs of tuneable sizes from 110 nm to 10 nm in organic semiconductor matrix. We observe a blue shift in the photoluminescence peak (PLmax) energy over a range of 200 meV for MAPbI3 PNCs embedded in the BCP matrix. However, PLmax energy tunes over 32 meV only with similar volumetric concenration in case of MAPbBr3 PNCs in the same BCP matrix. Moreover, the PL blue shift is even lower in case of CBP matrix in comparison to BCP matrix for both the perovskites. This discrepancy could be resolved by determining the resultant crystallite size using x-ray diffraction studies and Debye-Scherrer formula. Results about blue shift in PL peak could be explained using the classic particle in a box vs excitonic Bohr radius model under weak confinement regime. Particularly, MAPbI3 size dependent data fits with good accuracy and provide useful insight about semiconductor material.

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Fig: PL spectra of a) MAPbI3 :CBP, b) MAPbI3 :BCP, c) MAPbBr3 :CBP, and d) MAPbBr3 :BCP blend films with different concentrations of organic compounds.