Liquid-Phase Transfer of Organic-Inorganic Halide Perovskite Films for TEM Investigation and Planar Heterojunction Fabrication

Organic-inorganic halide perovskites (OIHPs) show high promise in optical and electronic applications such as solar cells, light-emitting diodes, and nonlinear optics. However, the fundamental knowledge of the atomic-scale microstructures in OIHP thin films is limited due to the challenge in characterizing them using transmission electron microscopy (TEM). Here a solution-phase "release-and-transfer" method is demonstrated, which entails the lifting of OIHP films from their original substrates while maintaining the film integrity, followed by a sequential transfer onto a TEM grid. The freestanding nature of the OIHP films with a nanoscale thickness, prepared as such, allows a direct TEM observation in the plan view, complementing those typical cross-sectional views enabled by focus-ion-beam specimen fabrication. Using low-dose scanning TEM, the atomic-scale microstructure of transferred OIHP films is confirmed to be generally maintained, while the microstrain existing in original films is largely relaxed. This "release-and-transfer" method is generic to both standard 3D and low-dimensional OIHPs. Based on a simple layer-by-layer transfer, the fabrication of a 2D-3D planar heterojunction with a good interfacial contact and optoelectronic properties is achieved. This unique methodology offers new opportunities to accelerate the fundamental and practical developments of OIHP materials and devices. A solution-phase release-and-transfer method for acquiring freestanding organic-inorganic halide perovskite thin films, which are suitable for the atomic-scale scanning transmission electron microscopy investigation, is demonstrated. Also, the method is generic to both 3D and 2D perovskites, unlocking a new fabrication route for perovskite planar heterojunctions.image