Extremely efficient internal exciton dissociation through edge states in layered 2D perovskites

Abstract

Understanding and controlling charge and energy flow in state-of-the-art semiconductor quantum wells has enabled high-efficiency optoelectronic devices. Two-dimensional (2D) Ruddlesden-Popper perovskites are solution-processed quantum wells wherein the band gap can be tuned by varying the perovskite-layer thickness, which modulates the effective electron-hole confinement. We report that, counterintuitive to classical quantum-confined systems where photogenerated electrons and holes are strongly bound by Coulomb interactions or excitons, the photophysics of thin films made of Ruddlesden-Popper perovskites with a thickness exceeding two perovskite-crystal units (>1.3 nanometers) is dominated by lower-energy states associated with the local intrinsic electronic structure of the edges of the perovskite layers. These states provide a direct pathway for dissociating excitons into longer-lived free carriers that substantially improve the performance of optoelectronic devices.

New Type of 2D Perovskites with Alternating Cations in the Interlayer Space, (C(NH2)3)(CH3NH3)nPbnI3n+1: Structure, Properties, and Photovoltaic Performance

“…We also investigated the photovoltaic performance of the highest member of the series GAMA 3 Pb 3 I 10 (n = 3), which adopts the centrosymmetric Imma space group and has the smallest optical gap in the series, E g = 1.73 eV, making it a good candidate for a light absorber material in both single-junction and tandem solar cells. Smooth, compact high-quality thin films were obtained by employing the solvent-engineering method with anti-solvent dripping at an optimized delay time.…”

“…(C(NH 2 ) 3 )(CH 3 NH 3 ) 3 Pb 3 I 10 . PbO (2232 mg, 10 mmol) was dissolved in a mixture of 20.0 ml of aqueous HI and 1.7 ml of aqueous H 3 PO 2 by heating to boiling under constant magnetic stirring for at least 15 min.…”

“…[1][2][3][4][5][6][7][8] Unlike the more extensively studied three-dimensional (3D) AMX 3 where the possibility of a 3D stable crystal structure is limited by the size and shape of the A + cation [9][10] the lower-dimensional perovskite semiconductors offer a much higher degree of structural versatility and permit better control and fine-tuning of the optoelectronic properties. 11 Conceptually, upon "cutting" the 3D parent compound along a specific crystallographic plane, infinite nanosheets with a slab thickness of atomic or molecular size can be obtained, which are separated by organic cations acting as spacers and in this context, they can be considered as natural quantum wells (QWs).…”

“…for 3s, followed by 4,000 rpm. for 60 s. 3 Pb 3 I 10 were obtained, Figure 1. Unlike the RP perovskites, ACI perovskites obey a different synthetic protocol requiring a fully stoichiometric reaction in order to to crystallize in pure form.…”

“…complex if one considers that the precise determination of the band edge continuum relative to the exciton energy level may be challenging, 3,65 and that the mechanism of the exciton expression also shows a strong temperature dependence.…”