How perovskites have the edge Two-dimensional Ruddlesden-Popper perovskites form quantum wells by sandwiching inorganic-organic perovskite layers used in photovoltaic devices between organic layers. Blancon et al. show that if the perovskite layer is more than two unit cells thick, photogenerated excitons undergo an unusual but highly efficient process for creating free carriers that can be harvested in photovoltaic devices (see the Perspective by Bakr and Mohammed). Lower-energy local states at the edges of the perovskite layer facilitate dissociation into electrons and holes that are well protected from recombination. Science, this issue p.1288; see also p. 1260 Excitons convert spontaneously to free carriers via lower-energy layer-edge states in layered perovskites. 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.

中文翻译：

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通过层状二维钙钛矿中的边缘态进行极其有效的内部激子解离

钙钛矿如何具有边缘二维 Ruddlesden-Popper 钙钛矿通过将光伏器件中使用的无机-有机钙钛矿层夹在有机层之间来形成量子阱。布兰肯等人。表明如果钙钛矿层的厚度超过两个晶胞，光生激子会经历一个不寻常但高效的过程，以产生可在光伏器件中收集的自由载流子（参见 Bakr 和 Mohammed 的观点）。钙钛矿层边缘的低能量局部状态有利于解离成电子和空穴，这些电子和空穴被很好地防止复合。科学，本期第 1288 页；另见第。1260 激子通过层状钙钛矿中的低能量层边缘状态自发地转换为自由载流子。了解和控制最先进的半导体量子阱中的电荷和能量流使高效光电器件成为可能。二维 (2D) Ruddlesden-Popper 钙钛矿是溶液处理的量子阱，其中可以通过改变钙钛矿层厚度来调整带隙，从而调节有效的电子空穴限制。我们报告说，与光生电子和空穴被库仑相互作用或激子强烈结合的经典量子限制系统违反直觉，由厚度超过两个钙钛矿晶体单元（> 1.3 纳米）的 Ruddlesden-Popper 钙钛矿制成的薄膜的光物理学由与钙钛矿层边缘的局部本征电子结构相关的低能态主导。