The long-term stability of three-dimensional (3D) perovskite solar cells (PSCs) has become the major challenge for their commercial applications. To solve this problem, the development of 2D/3D hybrid perovskites by incorporating bulky organic spacers into 3D perovskite films has been proposed as an efficient strategy to combine the high efficiency of 3D PSCs and high stability of 2D PSCs. In this review, we present the structure of 3D and 2D perovskite materials, discuss the transformation process from 3D to 2D perovskite, and summarize the key organic spacers used in 2D/3D PSCs. Most importantly, based on the appropriate selection of functional groups in organic spacers, we highlight the role of organic spacers in the fabrication process and formation mechanism of different types of 2D/3D perovskite heterojunctions including the bulk incorporation model, surface treatment model, and bulk incorporation and surface treatment coexisting model as well as other feasible models.

This review highlights the crucial role of organic spacers in the fabrication process and formation mechanism of different types of 2D/3D perovskites for PSCs including the bulk incorporation model, surface treatment model, and the coexisting model.