Tin (Sn)-based metal halide perovskites (MHPs) could be an environmentally benign alternative to lead-based ones, which are toxic. However, some critical issues need to be resolved before Sn-based MHPs can be leveraged in planar semiconductor devices. When arranged into a 2D structure (or quasi-2D structure with a few layers), defects in the crystal structure of Sn-based MHPs called 'grain boundaries' hamper the mobility of charge carriers throughout the material. If used in a TFT, this phenomenon results in a large series resistance that ultimately degrades performance. In addition, a TFT made using an Sn-based MHP arranged into a 3D structure faces a problem of extremely high carrier density of the 3D material, that causes the transistor to be permanently ON unless very high voltages are applied.
Scientists from Tokyo Tech, National Institute for Materials Science and Silvaco Japan have proposed a novel concept based on a hybrid structure for Sn-based metal halide perovskites (MHPs), called the '2D/3D core'shell structure.' In this structure, 3D MHP cores are fully isolated from one another and connected only through short 2D MHP strips (or 'shells'). This alternating arrangement manages to address both these issues, according to the team.
As for the high carrier density of 3D MHPs, this problem is reportedly not present when using the 2D/3D core'shell structure. Since the 3D cores are isolated, their carrier density is no longer relevant; instead, the 2D segments act as a bottleneck and limit the effective carrier density of the overall material.
To demonstrate the effectiveness of this newly developed structure, the team fabricated a complementary metal'oxide'semiconductor (CMOS) inverter by combining 2D/3D TFTs with a standard indium gallium zinc oxide TFT. 'Our device exhibited a high voltage gain of 200 V/V at a drain voltage of 20 V. This performance is the best reported so far for a CMOS inverter made using Sn-MHP TFTs,' highlights study author, Assistant Professor Junghwan Kim.
The innovative 2D/3D structure presented in this study could help scientists worldwide take advantage of the attractive electronic properties of perovskites. Moreover, their approach is not limited to a narrow class of materials or device types. 'The proposed strategy could be applied to various solution-derived semiconductor systems, opening doors to flexible and printable electronics,' says Prof. Kim.