**Definition of Open Circuit Voltage**

Open circuit voltage is a common term in solar cell applications. **V _{OC} ** is the open circuit voltage, which is the maximum voltage that is available for drawing out from a

**solar cell**, and occurs at

**zero current**. The open circuit voltage resembles the

**forward bias amount**on the solar cell as a result of the

**bias of the solar cell junction**with light generated current

*.*A

**V**equation can be defined by making the net current to equal zero in solar cell equation to be:

_{oc}

**Effects of different factors on Open Voltage current**

From the above equation it might seem that **V _{OC}** increases linearly with temperature. Yet, this is not true as

**I**quickly increases with temperature mainly as a result of changes in the

_{0}**n**which is intrinsic carrier concentration. The temperature effect is complex and changes with different cell technology.

_{i}**V**decreases with decrease of temperature. When temperature changes,

_{OC}**I**changes as well.

_{0}While **I _{sc}** normally has small variation, the main effect is

**saturation current**, as it may vary with orders of magnitude. The saturation current,

**I**relies on recombination of the solar cell.

_{0}**Open circuit voltage**then measures the recombination amount in the device. Open circuit voltages of silicon solar cells of high quality single crystal material is up to nearly

**764 mV**under one sun and

**AM1.5**conditions, while commercial devices usually have open circuit voltages of around

**600 mV**.

The** V _{OC}** can be also determined from carrier concentration and the equation is shown below:

Where:

**kT/q: the thermal voltage**

** N _{A}: the doping concentration**

** Δn: the excess carrier concentration**

**n _{i:} the intrinsic carrier concentration.**

**The V _{OC} determines the carrier concentration**

**Voc as a Function of Bandgap, E**_{G}

_{G}

The short circuit current I_{SC} decreases when the bandgap increases, the open circuit voltage increases when the bandgap increases. In a perfect device radiative recombination limits** V _{OC}** and the analysis uses the detailed balance principle to determine the minimum possible

**J**value.

_{0 }The minimum value for the diode saturation current is :

Where the terms

**q: defines the electronic charge**

**σ: defines the Stefan Boltzmann constant**

**k: is the Boltzmann constant**

**T: is the temperature**

And **u= E _{G }/ kT**

The evaluation of the above integral in the equation is fairly complex. The calculated **J _{0}** from above can be plugged directly into the standard solar cell equation previously provided to be used to determine the

**V**as long as the voltage remains equal to less than the band gap, as is the normal case and conditions known under one sun illumination.

_{OC}

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