Summary
Photovoltaic effect is the process in which two dissimilar materials in close contact produce an electrical voltage when struck by light.
Photoelectric effect is the emission of electrons from the surface of a substance in response to incident light.
In photovoltaic effect, electrons are retained in the material; in photoelectric effect, electrons are ejected out of the material.
Photovoltaic effect can occur with any frequency of incident light; photoelectric effect requires a minimum threshold frequency of incident light.
Photovoltaic effect produces both electric current and voltage; photoelectric effect produces only electric current.
In this blog post, we will compare and contrast two important phenomena related to light and matter: the photovoltaic effect and the photoelectric effect. Both effects involve the interaction of photons (light particles) with electrons (negative charge carriers) in a material, but they have different outcomes and applications.
What is the Photovoltaic Effect?
The photovoltaic effect is the process in which two dissimilar materials in close contact produce an electrical voltage when struck by light. This results in the creation of a voltage and an electric current in the material. The produced current is known as photo-current. Here, an ejection of electrons is not going to happen. The electrons absorb energy, but are retained in the substance.
The most common example of the photovoltaic effect is the solar cell, which consists of a layer of p-type semiconductor (with excess holes) and a layer of n-type semiconductor (with excess electrons) sandwiched together. When light shines on the solar cell, photons with enough energy can excite electrons from the valence band to the conduction band, creating electron-hole pairs. The electric field at the p-n junction separates these charge carriers, causing electrons to flow to the n-side and holes to flow to the p-side. This creates a potential difference across the solar cell, which can be used to power an external circuit.
The photovoltaic effect can also occur when two photons are absorbed simultaneously in a process called two-photon photovoltaic effect.
What is the Photoelectric Effect?
The photoelectric effect is the emission of electrons from the surface of a substance in response to incident light. Incident light is the ray of light that strikes a surface. This occurs on metal surfaces. The energy of light is absorbed by the electrons in the metal and these electrons are emitted. But, the energy of light should be exactly equal to or higher than the energy required for these electrons to be emitted this way.
The emitted electrons are known as photo-electrons. The energy of emitted electrons is independent of the intensity of incident light, but depends on the frequency of incident light. Incident light carries energy in the form of photons. The energy of photons is directly proportional to the frequency of light. If this energy is enough for an electron in the surface to overcome the electron binding energy (also called work function), it is ejected. If the energy is lower than the electron binding energy, then the electron is unable to escape.
The photoelectric effect was first observed by Heinrich Hertz in 1887 and explained by Albert Einstein in 1905 using his theory of light quanta (photons). The photoelectric effect has many applications, such as photomultiplier tubes, photo-detectors, and night vision devices.
How are they Different?
The main difference between photoelectric effect and photovoltaic effect is that in photoelectric effect, the electrons are emitted to open space whereas in photovoltaic effect, the electrons enter a different material.
Another difference is that photoelectric effect requires a minimum threshold frequency of incident light to occur, whereas photovoltaic effect can occur with any frequency of incident light as long as it can create electron-hole pairs.
A third difference is that photoelectric effect produces only electric current, whereas photovoltaic effect produces both electric current and voltage.
