Optical and optoelectronic properties of 2D, quasi-2D and 3D metal halide perovskites

Metal halide perovskites (MHPs) have emerged as highly promising semiconductor materials owing to their remarkable versatility across a broad spectrum of optoelectronic applications. A primary advantage of MHPs lies in their inherent compositional tunability, which facilitates the precise modulation of material properties to meet specific device performance criteria. In particular, three-dimensional (3D) organometal halide perovskites exhibit several advantageous intrinsic properties, including large crystalline domain size, low trap-state density, high charge carrier mobility, and the presence of free carriers under ambient conditions. These attributes collectively contribute to their superior performance in charge-separation-driven devices, such as perovskite solar cells and photodetectors. Nevertheless, a critical drawback associated with 3D perovskites is their limited environmental stability. This issue can be effectively mitigated through the incorporation of a thin two-dimensional (2D) perovskite capping layer, thereby forming a 2D/3D heterojunction architecture that enhances material stability without significantly compromising optoelectronic performance. In the context of light-emitting diode (LED) applications, efficient electron–hole injection and radiative recombination are essential. To simultaneously achieve high external quantum efficiency and enhanced operational stability in perovskite-based LEDs, quasi-2D perovskites—comprising a mixture of 2D and 3D phases—have been extensively explored. Quasi-2D perovskites form self-assembled multiple quantum well structures, in which injected charge gets confined and efficient radiative recombination occurs. In photodetector (PPD) applications, lower-dimensional MHPs offer improved operational stability but often encounter challenges related to irregular phase formation and suboptimal charge transport properties, whereas 3D MHP-based PPDs demonstrate faster photoresponse characteristics. In this review, we present a comprehensive overview of recent advances in the synthesis strategies, structural properties, and optical characteristics of 2D, quasi-2D, and 3D MHPs. Particular emphasis is placed on emerging trends from the past two to three years, with a focus on strategies for enhancing both the efficiency and operational stability of MHP-based optoelectronic devices.