Using a New Hybrid Structure to Make Metal–halide Perovskites Useful in Planar Devices

Metal halide perovskites (MHPs) are a type of semiconductor material with intriguing features, such as thin-film transistors (TFTs). Tin (Sn)-based MHPs, in particular, could be a more environmentally friendly alternative to harmful lead-based MHPs.

However, before Sn-based MHPs can be used in planar semiconductor devices, numerous fundamental difficulties must be rectified.

The mobility of charge carriers in Sn-based MHPs is hampered when flaws in the crystal structure called “grain boundaries” are grouped into a 2D structure (or quasi-2D structure with a few layers). When employed in a TFT, this phenomena causes a high series resistance, which reduces performance.

A TFT produced using a Sn-based MHP organized into a 3D structure, on the other hand, confronts a different but nonetheless devastating difficulty. Unless very high voltages are given, the transistor is permanently ON due to the 3D material’s exceptionally high carrier density.

The proposed strategy could be applied to various solution-derived semiconductor systems, opening doors to flexible and printable electronics.

Prof. Kim

Needless to say, this eliminates numerous applications for such a device. Fortunately, a group of scientists from Tokyo Tech University in Japan has discovered a way to overcome these constraints.

The researchers suggested a unique design for Sn-based MHPs called the “2D/3D core-shell structure” in a recent article published in Advanced Science and led by Assistant Professor Junghwan Kim and Honorary Professor Hideo Hosono.

3D MHP cores are totally isolated from one another in this structure, with only short 2D MHP strips (or “shells”) connecting them. This alternating layout addresses both of the aforementioned flaws at the same time. But how?

The key to lowering 2D MHPs’ series resistance is to reduce carrier mobility issues at grain boundaries, which are caused by misalignments between the perovskite’s conductive octahedra.

These misalignments are eliminated, and the series resistance is considerably reduced, thanks to the way the 3D cores connect to the 2D segments. When employing the 2D/3D core-shell configuration, the high carrier density of 3D MHPs is simply not a problem.

Because the 3D cores are isolated, their carrier density is no longer important; instead, the 2D segments operate as a bottleneck, limiting the entire material’s effective carrier density.

The researchers created a complementary metal-oxide-semiconductor (CMOS) inverter by merging 2D/3D TFTs with a typical indium gallium zinc oxide TFT to illustrate the usefulness of this unique construction.

“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 Prof. Kim.

The novel 2D/3D structure proposed in this study will aid scientists all around the world in taking use of perovskites’ appealing electrical features. Furthermore, their technique isn’t confined to a single sort of material or technology.

“The proposed strategy could be applied to various solution-derived semiconductor systems, opening doors to flexible and printable electronics,” says Prof. Kim.

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