The photovoltaic effect and the operation of photodiodes both rely on the presence of a p–n junction in a semiconductor. When such a junction is in the dark, an electric field is present internally in the junction region because there is a change in the level of the conduction and valence bands. This change leads to the familiar electrical rectification effect produced by such junctions.

When light falls on the junction, it is absorbed and, if the photon energy is large enough, it produces free hole-electron pairs. The electric field at the junction separates the pair and moves the electron into the n-type region and the hole into the p-type region. This leads to a change in voltage, which may be measured externally. This process is the origin of the so-called photovoltaic effect. We note that the voltage generated may be detected directly, and that no bias voltage nor ballast resistor is required.

It is also possible to use a p–n junction to detect light if one does apply a bias voltage in the reverse direction. By reverse direction, we mean the direction of low current flow, that is, with the positive voltage applied to the n-type material. A p–n junction operated with bias voltage is termed a photodiode

You may refer more here:

https://www.sciencedirect.com/topics/physics-and-astronomy/photodiodes

Mena Maurice Farag

Thank you for your response, you have explained briefly the phenomena which is appreciable, but my my question was related to materials/semiconductors like some specific materials show the photovoltaic effect and what is that intrinsic property ?

Drear Subhasri Subudhi ,

Adding to the colleague Mena Maurice Farag , the solar cell is a p-n junction diode with at least one side is partially metallized to allow the passage of light to the semicondcutor layers building the diode.

The photo voltaic effect is based on two effects:

- Photo generation of electrons hole pairs which is the photoelectric effect.

- The presence of the built in eclectic field which is formed by the p-n junction.

It is so that the built in electric field will separate the electrons and holes and and transport them to the anode and cathode of the diode where the electrons will be accumulated at the cathode and the holes at the anode. This accumulation leads to the formation of an electro motive force. This is the photovoltaic effect.

I would like to pay your attention to the book chapter:Chapter Solar cells and arrays: Principles, analysis and design

When you read it you will get thorough understanding to the operating principles of solar cells and their applications in PG generators.

Best wishes.

Dear Subhasri Subudhi

crystalline silicon is a semiconductor material widely used in photovoltaics. It becomes conductive when the energy of the photons absorbed by the crystal surface is sufficient to raise the electron state from the valence band to the conduction band. This required amount of energy to excite an electron is defined as band gap. The band gap is an intrinsic property of semiconductors and eventually has a direct influence on the photovoltaic cell voltage.

Mena Maurice Farag , Abdelhalim abdelnaby Zekry

Band gap concept I understand...Band gap plays the major role to absorb the corresponding range of light to that particular wavelength. But out of that what are the other factors responsible for photovoltaic effect. Suppose we have materials of same band gap values with same absorption coefficient and electron density then does they give same photovoltaic output ?

Dear Subhasri Subudhi ,

The energy gap of the semiconductor plays the major role in the photo conversion

efficiency PCE. It has been found that the highest theoretical PCE is achieved when Eg=1.35 eV.

From the practical consideration the performance of the solar cells is measures by the following performance parameters:

The photo current = Isc, the open circuit voltage Voc, the fill factor, Rs and Rp.

The open circuit voltage Voc= nVt ln Isc/ Is,

where n is the ideality factor , Is is the reverse saturation current and Vt is the thermal voltage.

The major loss effect is the recombination of photo generated electron hole pairs and the dark current also as a recombination losses.

I would pay your attention to read the literature which I brought previously.

Best wsihes

Abdelhalim abdelnaby Zekry

Thank you so much for your valuable answers.

In some materials thin films only show photovoltaic effect than thick film and bulk , thick film and bulk show only diode characteristics. can you please answer and suggest any article for this ?

And also as you have mention about the dark current, i have a doubt about that some materials show some Voc without light, generally in bulks...so how we can differentiate it ? if possible suggest some theories based on this.

please Subhasri Subudhi

give me examples!

All semiconductor diodes react to the incident solar radiation and produce photovoltaic effect. This means that they act as a solar cell irrespective of its its performance parameters. Solar cells are rectifying diodes that are optimized for maximum conversion efficiency.

I am astonishing that you decide before reading the book chapter.

Please read elaborately the chapter and then come to discuss the the issues with you.

Best wishes

Abdelhalim abdelnaby Zekry

Thank you for your reply

Actually I am working on ferroelectric photovoltaics which is a different phenomena to semiconductor p-n junction photovoltaics. That's why i confuse

.