Field-effect transistors (FET) with advanced carrier mobilities are thought possible with metal halide perovskite semiconductors. By manipulating this material, optimized optoelectronic properties can be reached. In this article, the benefit of using semiconductor field-effect transistors is explained, highlighting some of their key applications and future developments for this material.
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Crystalline Structures
The formula for a perovskite compound is typically expressed as ABX3. These are crystalline structures that bond two cations ("A" and "B", divalent metal ion) to an anion ("X"); the "B" atoms tend to be smaller than the 'A' atoms. Frequently the anion is an oxide, but when it is a halide, these perovskites give rise to a group of highly attractive semiconductors.
Combining enhanced electronic and optical properties, coupled with cost-effective fabrication such as printing, has made them the focus of many research groups.
Superior Photovoltaic Efficiencies
With their unique features, metal halide perovskite semiconductors are becoming implemented into multi-junction solar energy or solar-to-fuel energy conversion devices. As a result, direct and indirect processing can exploit the energy in sunlight to produce a fuel or transform solar energy into other forms, including biomass, which can be converted into a fuel producer.
These photovoltaic-based devices require an understanding of the material's fundamental properties that underpin them. As knowledge of the operational mechanisms deepens, it results in superior photovoltaic efficiencies being realized. Advancing device architectures and fine-tuning the absorber materials has allowed metal halide perovskite semiconductors to compete with the more conventional silicon-based photovoltaic technologies.
Field-effect Transistors
Comprised of three terminals, a field-effect transistor (FET) is a transistor type that controls current flow within a semiconductor via an electric field acting gate or a switch for electronic signals. Control is facilitated by applying a voltage to a gate that subsequently alters the conductivity between the two other terminals, the drain and the source.
Typically they involve single-carrier-type operations, where the charge carrier is an electron or a hole. When the channel composition is primarily a hole charge carrier, it is referred to as a p-channel, whereas an n-channel involves electrons constituting a current flow.
FETs can be constructed from various semiconductors. If a heterojunction comprised of two differing band-gaped materials is incorporated as the channel rather than a doped region, then electrostatic discharge and, or overload voltages can be prevented in addition to avoiding undesirable, variable threshold voltages.
Improved Transport
FETs with advanced carrier mobilities are thought possible by metal halide perovskite semiconductors, which can be a good foundation for investigating carrier transport and structure-property relationships.
An investigation into the research output on the topic has been conducted by Zhu H. et. al and published in the Journal of Information Display on July 29th 2021. The electrical characteristics and stability properties were of particular interest as these have evolved within 2D and 3D tin-based perovskite FETs and those that are lead-based. In essence, based on previous studies, the researchers concluded that improved hole transport in 2D tin-based metal halide perovskite FETs is seemingly due to valance band hybrid-states. In comparison to lead-based, they have lower formation energy for tin vacancies.
Bulky Organic Components
Groups have made attempts to expose the genuine charge carrier transport properties by minimizing ionic defects migration. Trade-offs between the carrier mobility and the stabilization of the perovskite structure to protect inorganic compositions from oxidation have been one focus.
Bulky organic parts insulate and possibly reduce mobility in carriers, which is unfortunate as in low-cost light-emitting diodes (LED), high photoluminescence quantum yields (PLQYs) are possible when long-chain ammonium halides are incorporated into two-dimensional (2D) lead halide perovskites. Instead, their presence has been found to be deleterious to charge transport properties along nanoplatelets and nanocrystals, hampering LED performance.
Development work into replacing long organic molecules with alkaline ions such as sodium (Na+) has proven successful, generating enhanced photoluminescence lifetimes from the sodium-incorporated film. Experiments have also explored two-dimensional–three-dimensional (2D–3D) perovskites, finding that quantum efficiency of 15.9% can be achieved with various inorganic ions as spacers and incorporating low concentrations of an organic additive to achieve compact and uniform films.
Charge-Transport Physics
Other initiatives have focused on illuminating the charge-transport physics of perovskite materials. This work has seen an evolution from a low-temperature operation to suppress ionic migration in 3D perovskite FETs, to room temperature operation. Material refinement has led to lower ionic defect concentration emerging and migrating, causing less obstruction and enabling decent current or FET gate modulation detection.
Future Directions
The environmental stability of devices built from metal halide perovskite semiconductors is likely to occupy researchers for some time. Alongside this, attention will be drawn to finding complementary electronic and metal oxide devices once the potential of 3D tin-based perovskites has been realized.
Higher carrier mobilities will be seen in the next generation of FETs with these perovskites, opening up the possibilities for their use in several computing technologies. For example, controlling the image produced by a liquid crystal display (LCD) is possible with active-matrix technology where a matrix of active capacitors and thin-film transistors (TFTs) are incorporated. In mini-computing, printed circuit boards have been replaced by wire-wrapped backplanes acting as a backbone within the infrastructure to host plug-in cards for storage and processing.
Additional exciting transistor architectures should be anticipated as more effort is expended into understanding perovskite semiconductor structures.
References and Further Reading
Zhu, H., Liu, A. and Noh, Y., (2021) Recent progress on metal halide perovskite field-effect transistors. Journal of Information Display, pp.1-12. Available at: https://doi.org/10.1080/15980316.2021.1957725
Wu, C., et al. (2019) Alternative Type Two-Dimensional–Three-Dimensional Lead Halide Perovskite with Inorganic Sodium Ions as a Spacer for High-Performance Light-Emitting Diodes. ACS Nano,. Available at: https://doi.org/10.1021/acsnano.8b07632
Heo, J., et al. (2013) Efficient inorganic–organic hybrid heterojunction solar cells containing perovskite compound and polymeric hole conductors. Nature Photonics, 7(6), pp.486-491. Available at: https://doi.org/10.1038/nphoton.2013.80
Chin, X., Cortecchia, D., Yin, J., Bruno, A. and Soci, C., (2015) Lead iodide perovskite light-emitting field-effect transistor. Nature Communications, 6(1). Available at: https://doi.org/10.1038/ncomms8383
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