Abstract
Two dimensional inorganic–organic hybrid perovskites (2D perovskites) suffer from not only quantum confinement, but also dielectric confinement, hindering their application perspective in devices involving the conversion of an optical input into current. In this report, we theoretically predict that an extremely low exciton binding energy can be achieved in 2D perovskites by using high dielectric-constant organic components. We demonstrate that in (HOCH2CH2NH3)2PbI4, whose organic material has a high dielectric constant of 37, the dielectric confinement is largely reduced, and the exciton binding energy is 20-times smaller than that in conventional 2D perovskites. As a result, the photo-induced excitons can be thermally dissociated efficiently at room temperature, as clearly indicated from femtosecond transient absorption measurements. In addition, the mobility is largely improved due to the strong screening effect on charge impurities. Such low dielectric-confined 2D perovskites show excellent carrier extraction efficiency, and outstanding humidity resistance compared to conventional 2D perovskites.
Highlights
Two dimensional inorganic–organic hybrid perovskites (2D perovskites) suffer from quantum confinement, and dielectric confinement, hindering their application perspective in devices involving the conversion of an optical input into current
Quantum confinement can be reduced by increasing the width of the inorganic semiconductor layer in 2D perovskites, but even when the width of the inorganic layer is enlarged by five times, the binding energy is still up to 200 meV18
We focus on 2D perovskite single crystals without any transportation layer so that we can get insight into the “intrinsic” humidity stability related to the organic layers only
Summary
According to our simulation (see Supplementary Note 2), when the dielectric constant of the organic component is small, such as PEA whose dielectric constant is ~3.314, the Bohr radius describing the mean distance between the electron and hole in the exciton will decrease and the exciton-binding energy will be largely enhanced (Fig. 1c), indicating a strong dielectric confinement. As the dielectric constant of the organic layers increases, the dielectric screening effect will be enhanced, so that the Coulomb force between electron and hole of the exciton will decrease, leading to an increased Bohr radius and decreased exciton-binding energy. The PL intensity of the 2D_EA perovskites dropped rapidly as the temperature increases from 50 to 160 K (Fig. 2a), indicating that the attractive force between electron and hole in the exciton is extremely weak because of the strong screening effect (inset of Fig. 2a).
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