Conventional Phototransistor vs Solaristor

A solaristor (from

SOLAR cell A solar cell, also known as a photovoltaic cell (PV cell), is an electronic device that converts the energy of light directly into electricity by means of the photovoltaic effect.

transISTOR A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch electrical signals and electric power, power. It is one of the basic building blocks of modern electronics. It is composed of semicondu ...

) is a compact two-terminal self-powered

phototransistor A photodiode is a semiconductor diode sensitive to photon radiation, such as visible light, infrared or ultraviolet radiation, X-rays and gamma rays. It produces an electrical current when it absorbs photons. This can be used for detection and me ...

. The two-in-one transistor plus solar cell achieves the high-low current modulation by a memresistive effect in the flow of photogenerated carriers. The term was coined by Dr Amador Perez-Tomas working in collaboration with other ICN2 researchers in 2018 when they demonstrated the concept in a

ferroelectric In physics and materials science, ferroelectricity is a characteristic of certain materials that have a spontaneous electric polarization that can be reversed by the application of an external electric field. All ferroelectrics are also piezoel ...

-oxide/ organic bulk heterojunction solar cell.

Principle of operation

In a basic solaristor embodiment, the self-powered transistor effect is achieved by the integration of a light absorber layer (a material that absorbs

photon energy Photon energy is the energy carried by a single photon. The amount of energy is directly proportional to the photon's electromagnetic frequency and thus, equivalently, is inversely proportional to the wavelength. The higher the photon's frequenc ...

) in series with a functional

semiconductor A semiconductor is a material with electrical conductivity between that of a conductor and an insulator. Its conductivity can be modified by adding impurities (" doping") to its crystal structure. When two regions with different doping level ...

transport layer, which internal conductivity or contact resistance can be modified externally.

Light absorber (solar cell element)

In general, the light absorber is a semiconductor p–n junction that: * Efficiently harvests photons at various visible wavelengths by the

photoelectric effect The photoelectric effect is the emission of electrons from a material caused by electromagnetic radiation such as ultraviolet light. Electrons emitted in this manner are called photoelectrons. The phenomenon is studied in condensed matter physi ...

. * Splits photo-generated

exciton An exciton is a bound state of an electron and an electron hole which are attracted to each other by the electrostatic Coulomb's law, Coulomb force resulting from their opposite charges. It is an electrically neutral quasiparticle regarded as ...

s into free electrons and holes. * Brings these free electrons and holes toward their respective outer electrodes by means of an internal field. Additionally, in

thin-film solar cell Thin-film solar cells are a type of solar cell made by depositing one or more thin layers (thin films or TFs) of photovoltaic material onto a substrate, such as glass, plastic or metal. Thin-film solar cells are typically a few nanometers (nan ...

s, buffer electron and hole semiconductor transport layers are introduced at the respective metal electrodes to avoid electron-hole recombination and to remove the metal/absorber

Schottky barrier A Schottky barrier, named after Walter H. Schottky, is a potential energy barrier for electrons formed at a metal–semiconductor junction. Schottky barriers have rectifier, rectifying characteristics, suitable for use as a diode. One of the p ...

Conductivity modulator (transistor element)

A solaristor effect is achieved by modifying the internal field properties or the overall conductivity of the solar cell. Ferroelectric solaristors. One possibility is the use of

semiconductors as transport layers. A ferroelectric layer can be seen as a semiconductor with switchable surface charge polarity. Because of this tuneable dipole effect, ferroelectrics bend their

electronic band structure In solid-state physics, the electronic band structure (or simply band structure) of a solid describes the range of energy levels that electrons may have within it, as well as the ranges of energy that they may not have (called ''band gaps'' or '' ...

and offsets with respect to adjacent metals and/or semiconductors when switching the ferroelectric polarization so that the overall conductivity can be tuned orders of magnitude.

Two-terminal phototransistors

Conventional

photodiode A photodiode is a semiconductor diode sensitive to photon radiation, such as visible light, infrared or ultraviolet radiation, X-rays and gamma rays. It produces an electrical current when it absorbs photons. This can be used for detection and me ...

s or

photodetector Photodetectors, also called photosensors, are devices that detect light or other forms of electromagnetic radiation and convert it into an electrical signal. They are essential in a wide range of applications, from digital imaging and optical ...

s do not switch as a

does when biased through its third terminal (gate). An additional advantage of a solaristor is, therefore, the potential reduction of the standard phototransistor's area and interconnection complexity. By using solaristors, it would be possible in theory to replace the in-plane three-electrode architecture by a vertical, two-electrode photodiode-like architecture in systems like photo-sensors, cameras, or displays.

References

{{Authority control Transistors Photovoltaics Electrical components Semiconductor devices

Principle of operation

Light absorber (solar cell element)

Conductivity modulator (transistor element)

Two-terminal phototransistors

See also

References