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Can this solar cell material be used for FETs?

Posted: 11 May 2015     Print Version  Bookmark and Share

Keywords:perovskite  photovoltaic  solar cell  Jurchescu 

With the relative ease in manufacturing the room temperature solution-based material, perovskite has become the new darling of the photovoltaic (PV) solar cell industry. In addition, its efficiency has grown from just 3.8 per cent in 2009 to over 20 per cent in 2014.

Perovskite-based solar cells are expected to be commercially available by 2016.

Perovskite also has many other tunable semiconducting properties, such as high-temperature superconductivity, colossal magnetoresistance, ferroelectricity as well as diverse magnetic and optoelectronic properties. That got researchers thinking—if silicon solar cells can also be made into diverse semiconducting chips, why not perovskite-based materials too?

The early attempts to make field-effect transistors (FETs) from the material, however, had "limited success," according to professor Oana Jurchescu at Wake Forest University (Winston-Salem, North Carolina), who also claims to head "the first research group to successfully make complementary FETs from halide-perovskite," possibly opening a new era in flexible, low-cost, low-power optoelectronic semiconductors akin to complementary metal-oxide semiconductors (CMOS) but handling optical signals too on flexible substrates.

Crystal structure

The crystal structure of CH3NH3PbI3?x Clx hybrid halide perovskite. The lead (yellow spheres) and halide (I/Cl, magenta spheres) sit at the centres and corners of the octahedron, respectively, and the organic cation sits in the interstices. (Source: Wake Forest University)

"Hybrid halide perovskite field-effect transistors (HHP-FETs) could promote the development of complementary optoelectronics,"Jurchescu told EE Times, hastening to add that the work was performed in collaboration with the University of Utah.

The optical angle comes in, because "light-emitting diodes (LEDs) based on these compounds rival the best on the market," according to Jurchescu. In addition, hybrid organic-inorganic halide perovskite semiconductors can also exhibit wavelength-tunable photoluminescence emission including making electrically pumped lasers and has charge-carrier diffusion-lengths of hundreds of micrometres. To boot, the material exhibits spin-related properties albeit with relatively short spin lifetimes due to strong spin-orbit coupling.

HHP-FETs

The good news is that Jurchescu was able to demonstrate complementary n-type and p-type devices with equal carrier mobility to enable CMOS-like perovskite-based semiconductors in the future. The bad news is that his current prototype exhibits a dismal 1cm2/Vs electron mobility compared to 1,400cm2/Vs electron mobility for silicon.

Schematic structure of the FETs

Schematic structure of the FETs based on hybrid halide semiconductor layer, having Au source and drain contacts, Cytop dielectric and Al gate electrode. (Source: Wake Forest University)

However, the theoretical maximum electron mobility for HHP-FETs is 2,000cm2/Vs—even higher than silicon—but with 300cm2/Vs hole mobility (compared to 450cm2/Vs for silicon). The researchers also found that the yield, operational and environmental stability for its HHP-FETs was inferior to silicon, which is perhaps to be expected from any new semiconducting material.


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