A deficiency in the photoelectrical dynamics at the interface due to the surface traps of the TiO2 electron transport layer (ETL) has been the critical factor for the inferiority of the power conversion efficiency (PCE) in the perovskite solar cells. Despite its excellent energy level alignment with most perovskite materials, its large density of surface defect as a result of sub lattice vacancies has been the critical hurdle for an efficient photovoltaic process in the device. Here, we report that atoms thick 2D TiS2 layer grown on the surface of a (001) faceted and single-crystalline TiO2 nanograss (NG) ETL have effectively passivated the defects, boosting the charge extractability, carrier mobility, external quantum efficiency, and the device stability. These properties allow the perovskite solar cells (PSCs) to produce a PCE as high as 18.73% with short-circuit current density (J sc), open-circuit voltage (V oc), and fill-factor (FF) values as high as 22.04 mA/cm2, 1.13 V, and 0.752, respectively, a 3.3% improvement from the pristine TiO2-NG-based PSCs. The present approach should find an extensive application for controlling the photoelectrical dynamic deficiency in perovskite solar cells.

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The structure and the electronic properties of the electron-transport layer (ETL) of perovskite solar cells (PSCs) govern the interfacial charge transfer and charge transportation to the electrode. The ETLs of two dimensions, that are atom thick, and have a planar structure that possesses special electronic properties, such as the surface collective motion of excitons or charge transfer-driven defect state relief, that is 2D transition metal dichalcogenide, allow a highly energetic carrier dynamic process for enhanced photovoltaic effect. Herein, it is discovered that planar, few-atom-thick 2H-WS 2 nanosheets' ETLs drive ultrafast charge transfer and transportation along the ETL during the photovoltaic process. Time-resolved photoluminescence and electrochemical impedance spectroscopy analysis results indicate that the charge transfer from the perovskite to the ETL occurs as fast as 5.9 ns with charge transfer resistance as low as 25.6 Ω. This allows the PSC device to produce a power conversion efficiency of 18.21% with short-circuit current density, open-circuit voltage, and fill factor as high as 22.24 mA cm 2 , 1.12 V, and 0.731, respectively. The PSC retains 96.87% of its performance when being aged in nitrogen atmosphere for 33 days. Atom-thick planar WS 2 ETL nanosheets can be the basis for the development of high-performance PSC devices.

Single crystalline, ultrathin TiO₂ nanograss grown directly on ITO provides a highly efficient interfacial charge transfer in perovskite solar cells.