Controllable Acceleration and Deceleration of Charge Carrier Transport in Metal‐Halide Perovskite Single‐Crystal by Cs‐Cation Induced Bandgap Engineering

Abstract Charge carrier transport in materials is of essential importance for photovoltaic and photonic applications. Here, the authors demonstrate a controllable acceleration or deceleration of charge carrier transport in specially structured metal‐alloy perovskite (MACs)PbI 3 (MA= CH 3 NH 3 ) single‐crystals with a gradient composition of CsPbI 3 /(MA 1− x Cs x )PbI 3 /MAPbI 3 . Depending on the Cs‐cation distribution in the structure and therefore the energy band alignment, two different effects are demonstrated: i) significant acceleration of electron transport across the depth driven by the gradient band alignment and suppression of electron–hole recombination, benefiting for photovoltaic and detector applications; and ii) decelerated electron transport and thus improved radiative carrier recombination and emission efficiency, highly beneficial for light and display applications. At the same time, the top Cs‐layer results in hole localization in the top layer and surface passivation. This controllable acceleration and deceleration of electron transport is critical for various applications in which efficient electron–hole separation and suppressed nonradiative electron–hole recombination is demanded.