**Effect of Parasitic Resistances on Solar Cells**

**Resistive effects of solar cells** can reduce the solar cell efficiency by dissipation of power in the resistances. **Series resistance** and **shunt resistance** are the two most known** parasitic resistances**.

The key impact of parasitic resistance is reducing the fill factor in the majority of cases and for usual values of series and **shunt resistance**. Both the impact and the magnitude of series and shunt resistance is dependent on the **geometry and shape of the solar cell**, at the point of operation of the solar cell. As the value of resistance will be **proportional to the area of the solar cell**, when series resistance of solar cells that might have different areas is compared, a typical unit for resistance is in **Ωcm ^{2}**. This resistance normalized to area results from replacement of the current with current density in

**Ohm’s law**as given in the equation below:

**R’ (Ωcm ^{2 }) = V/J**

Resistive effects of solar cells reduce the efficiency of the solar cell by dissipation of power in the resistances. Series resistance in a solar cell is due to the following:

**The movement of the current through the pn materials of the solar cell****The contact resistance between the silicon and the metal contact****The top metal contacts and rear metal contacts resistance.**

Despite the series resistance effect of reducing the fill factor, it has no impact on neither the open circuit voltage nor on the short-circuit current

**Parasitic Resistance**

Similar to the way an electrical source can be represented with the internal resistance losses, solar cells commonly suffer from two **distinct parasitic current losses** (**ISR and IPR**) caused respectively by the series and the parallel resistance. The series resistance **(RS)**, is basically a result of the **bulk resistances of the semiconductor** and all its metallic contacts in addition to the contact resistance between these **two materials**. The parallel resistance** ( RP)**, usually can be due to leakage at the edge of the cell or any extended defects in the depletion zone.

These **extended defects** which are associated with **low cost solar cells** can include **dislocations**, **grain boundaries** and **large precipitates**. These aforementioned sites become areas which are likely to suffer **doping diffusion** or fine metallic bridges caused by contact metallisation.

If a **resistance is connected to a solar cell**, like when applying a resistance** RA**, two different parasitic effects can be found:

**Current declines the higher the series resistance RS, while voltage declines the lower the parallel resistance RP**. The two of the damaging cases reduce the **FF** as both **IM** and **VM** respectively are shifted towards the origin on an **I-V graph**.

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