I am trying to understand the physics behind solar cells. As far as I know, they work simply on the principle of pn junction diode. The optically generated charge carried are transported to the respective side by the built-in potential set up across the junction. It means that the photogenerated carrier is drifted by the built-in electric field. Once they talk about the IV characteristics of solar cell, they use the term bias current, I am not sure from where does this term come from as we are not biasing it to any external source. Can someone please help me clear my concept for this ?
Dear Bibek S Dhami ,
welcome,
The definition of biasing stems from a two terminal device or circuit. When one terminal is at higher potential than the other, it is said that the device is positively biased. The opposite is true if the same terminal have less potential than the other, the device is said to be negatively biased.
The biasing can be due to an external applied voltage on the device.
This is an external biasing.
It could be due to self biasing form an internal source.
It is an internal biasing.
Incase of solar cell, it could be internally biased because of the electromotive force generated by the photovoltaic effect. That when the solar cell is illuminated and operated in the fourth quadrant.
It could be also externally biased in any quadrant of the I-V curve.
In the fourth quadrant, the applied positive voltage source will act as a load.
Biasing is a potential relation of two nodes relative to each other.
Best wishes
@Bibek S Dhami, You are right that photovoltaic cells or devices also called solar cells are operated at positive voltage ranges. Sometimes such structure of devices could consider to use as a photodiode which is operated at a negative bias range. To test a bias of a solar cell, it could also help understand the charge traps inside the devices. You are right that most of people don't do it.
Dear Bibek S Dhami ,
welcome,
The definition of biasing stems from a two terminal device or circuit. When one terminal is at higher potential than the other, it is said that the device is positively biased. The opposite is true if the same terminal have less potential than the other, the device is said to be negatively biased.
The biasing can be due to an external applied voltage on the device.
This is an external biasing.
It could be due to self biasing form an internal source.
It is an internal biasing.
Incase of solar cell, it could be internally biased because of the electromotive force generated by the photovoltaic effect. That when the solar cell is illuminated and operated in the fourth quadrant.
It could be also externally biased in any quadrant of the I-V curve.
In the fourth quadrant, the applied positive voltage source will act as a load.
Biasing is a potential relation of two nodes relative to each other.
Best wishes
Dear Abdelhalim abdelnaby Zekry
How can the short circuit current increase if the bandgap is reduced whereas the open-circuit voltage increases with the increase in bandgap? Also, how can we increase the fill factor?
The short circuit current density increases if the band gap is reduced due to increased absorption in the long-wavelength portion of the spectrum, the open circuit is related to the band gap by Voc = Eg / 2, concerning the FF there are several methods to increase it.
I'm rather new to research in this area but it was quite confusing for me in the beginning and yet still I might not have true understanding but anyway...
How I like to think of the differences between the voltages produced by the cell and biasing is remembering that J-V characteristics are obtained by us scanning through the voltages of the solar cell, which is achieved by biasing the device (applying an external voltage). In practical applications where the cell is producing power to a load circuit the solar cell will be potentially operating at one point on this curve (with a given output voltage and current). In-fact, the point of operation will depend on the lighting conditions as well as the load of the circuit. The purpose of maximum power point circuits in practical applications for example is to actively (or passively, i.e. the fractional open circuit voltage method) bias the device to make sure the device is operating point at (or near) the maximum power point. Experimentally it is used to probe different electrical characteristics as it allows the solar cell to operate at open circuit or short circuit conditions and much more. In summary, biasing using an external voltage allows us to operate the solar cell at any point of their J-V characteristics that we desire.
Hopefully that is helpful and if it is incorrect hopefully our colleagues can help me understand better too.
Best wishes
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