Control of photoelectric properties in all-inorganic CsPbBr₃ thin films with two-dimensional interface modification

  Objective  As a new generation photovoltaic technology, perovskite solar cells (PSCs) have achieved a comparable efficiency to commercial silicon-based solar cells, demonstrating great application potential. However, these photoactive layers based on organic-inorganic hybrid perovskites are very unstable, which seriously hinders their commercial application. Therefore, all-inorganic CsPbBr₃ perovskite has attracted enormous attention due to its outstanding environmental tolerance to heat, moisture, oxygen and UV light. Unfortunately, the device efficiency based on CsPbBr₃ perovskite is relatively lower compared to that of the PSCs device with organic-inorganic hybrid perovskites. The recombination of charge carriers at the interface between the charge transport layers and the perovskite layer in all-inorganic CsPbBr₃ PSCs is the key factor that restricts the further improvement of its photoelectric conversion efficiency (PCE). In recent years, two-dimensional transition metal dichalcogenides (TMDCs) materials represented by MoS₂, MoSe₂, WS₂ and WSe₂ have attracted more and more attention due to their unique physical and chemical properties. With the advantages such as adjustable band gap and band edge, high carrier mobility, stable chemical properties and matching energy level with perovskite materials, two-dimensional TMDCs are regarded as effective interface modification materials to promote interface charge extraction in all inorganic CsPbBr₃ PSCs. However, the current research on using two-dimensional materials as interface modification layers and charge carrier transport layers in all-inorganic PSC is still in its infancy.

  Methods  Through interface engineering, various two-dimensional TMDCs (MoS₂, MoSe₂, WS₂, and WSe₂) materials are introduced at the interface between the perovskite layer and the electron transport layer of the all-inorganic CsPbBr₃ PSCs with an FTO/SnO₂/TMDCs/CsPbBr₃/C structure. The two-dimensional TMDCs here act as both interface modification materials and carrier transport layers. Through interface level compensation and barrier reduction with TMDCs interlayers, the carrier extraction and transport in all-inorganic CsPbBr₃ PSC devices are promoted (Fig.1). Moreover, by constructing TMDCs/CsPbBr₃ van der Waals heterostructure, high-quality CsPbBr₃ perovskite thin films with large and compact grains are grown via lattice matched van der Waals epitaxy (Fig.5).

  Results and Discussions  The interface charge loss between the perovskite layer and the electron transport layer is reduced, and the carrier extraction in the all-inorganic CsPbBr₃ PSC devices are enhanced, so that the PCE of the devices is increased from the initial 7.94% to 10.02%, and the open-circuit voltage is increased from 1.474 V to 1.567 V (Fig.8). In addition, Mott–Schottky curves are measured in the dark by performing capacitance-voltage characterization, which demonstrates an enhanced built-in potential, indicating the enlarged driving force for charge transportation with TMDCs/CsPbBr₃ heterostructure (Fig.9). Finally, the time-resolved photoluminescence decay measurements are performed to investigate the photoluminescence decay lifetimes, which are closely related to the electron extraction ability. Due to better energy level matching of TMDCs with perovskite layers, CsPbBr₃ perovskite layers show shorter carrier lifetimes on TMDCs interlayer (Fig.10), which further confirms the enhanced electron extraction ability from perovskite to the electron transport layer.

  Conclusions  A novel strategy is developed to prepare high-quality perovskite films by constructing TMDCs/CsPbBr₃ van der Waals heterostructure and achieve high-performance photoelectric devices through interfacial energy level matching, which provides a new way for the development of all-inorganic perovskite optoelectronic devices based on two-dimensional TMDCs materials.