We theoretically investigate the energy transfer between a CdSe/CdS Quantum-dot/Quantum-rod (QD/QR) core/shell structure and a weakly doped graphene layer, separated by a dielectric spacer. A numerical method assuming the realistic shape of the type I and quasi-type II CdSe/CdS QD/QR is developed in order to calculate their energy structure. An electric field is applied for both types to manipulate the carriers localization and the exciton energy. Our evaluation for the isolated QD/QR shows that a quantum confined Stark effect can be obtained with large negative electric filed while a small effect is observed with positive ones. Owing to the evolution of the carriers delocalization and their excitonic energy versus the electric field, both type I and quasi-type II QD/QR donors are suitable as sources of charge and energy. With a view to improve its absorption, the graphene sheet (acceptor) is placed at different distances from the QD/QR (donor). Using the random phase approximation and the massless Dirac Fermi approximation, the quenching rate integral is exactly evaluated. That reveals a high transfer rate that can be obtained with type I QD/QR with no dependence on the electric field. On the contrary, a high dependence is obtained for the quasi-type II donor and a high fluorescence rate from F = 80 kV/cm. Rather than the exciton energy, the transition dipole is found to be responsible for the evolution of the fluorescence rate. We find also that the fluorescence rate decreases with increasing the spacer thickness and shows a power low dependence. The QD/QR fluorescence quenching can be observed up to large distance which is estimated to be dependent only on the donor exciton energy.

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The multi-quantum well (MQW) organic-inorganic perovskite offer an approach of tuning the exciton binding energy based on the well-barrier dielectric mismatch effect, which called the image charge effect. The exfoliation from MQW organic-inorganic perovskite forms a twodimensional (2D) nano-sheet. As with other 2D materials, like graphene or transition metal dichalcogenides (TMDs), the ultra-thin perovskites layers are highly sensitive to the dielectric environment. We investigate the ultrathin crystalline 2D van-der-Waals (vdW) layers of organic-inorganic perovskite crystals close to a surface of the substrate. We show that binding exciton energy is strongly influenced by the surrounding dielectric environment. We find that the Keldysh model somehow estimates the strong dependence of the exciton binding energies on environmental screening. We compare our binding energies results with experimental results in the (C 6 H 13 NH 3 ) 2 PbI 4 perovskite, and we estimate the binding energy values of (C 4 H 9 NH 3 ) 2 PbBr 4 . I-IntroductionFor about a decade, 2D materials have represented one of the hottest directions in solid-state research. Much attention has been paid to 2D layered compounds such as graphene or TMDs.Due to weak vdW bonding, it is easy to cleave neighboring layers and form ultra-thin samples. [1][2][3][4][5] In these materials, new optical and electronic properties emerge for mono-or fewlayer regions, providing new avenues for material applications. Here, we explore a recent addition to this library, ultrathin crystalline layers of organic-inorganic perovskite crystals.These materials differ from the previous types of 2D vdW layers in being a hybrid material with an organic compound intrinsically integrated into an inorganic crystal structure.

The investigation of the fluctuations and their influence on the exciton in the perovskite structure is topical. These fluctuations can be due to the prolongation of the annealing or the increasing of the temperature in the perovskite monolayers. This fact generates structural imperfections, which may arise from vacancies and lattice structural defects. In this work, we propose a theoretical approach in order to study the optical properties characterized by excitons in (RNH3)2(CH3NH3)p−1PbpI3p+1 perovskite structures. For high quality samples, we investigate the free exciton taking into account the quantum and the dielectric confinements. For low quality samples, we model the surface disorder of perovskite monolayers through a randomized potential in the layer plane. Finally, we investigate the dependence of the perovskite layer thickness (p-value) on the shift between the relaxed exciton compared to the free exciton, and we show that our model allows us to simulate the experimental spectra of the exciton states.