Shunt Resistance

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The Impact of Shunt Resistance on Solar Cell Performance

Shunt resistance (R_SH) plays a significant role in the efficiency of solar cells. It is often caused by manufacturing defects and can lead to power losses in solar cells. Low shunt resistance provides an alternative current path for the light-generated current, reducing the current flow through the solar cell junction and lowering the voltage output. This effect is more pronounced at lower light levels, where the loss of current to the shunt has a greater impact.

Equation for Solar Cell with Shunt Resistance

The behavior of a solar cell with shunt resistance can be described by the equation:

I = I_L – I₀ exp(qV/nkT) – VR_SH

Where I is the cell output current, I_L is the light-generated current, V is the voltage across the cell terminals, T is the temperature, q and k are constants, n is the ideality factor, and R_SH is the shunt resistance.

Impact on Fill Factor

The shunt resistance also affects the fill factor of the solar cell. The maximum power output can be approximated as the power without shunt resistance, minus the power lost in the shunt resistance. This leads to the equation:

P_MP‘ = P_MP(1 – R_SH/R_S)

Where P_MP is the maximum power output, R_S is the series resistance, and R_SH is the shunt resistance.

Normalized Shunt Resistance

A normalized shunt resistance (r_SH) can be defined as R_SH/R_S. Assuming that the open-circuit voltage and short-circuit current are not affected by the shunt resistance, the impact of shunt resistance on the fill factor can be determined as:

FF’ = FF(1 – 1/r_SH)

Where FF is the fill factor unaffected by shunt resistance, and FF’ is the fill factor affected by shunt resistance.

Empirical Equation for Fill Factor

An empirical equation that relates the fill factor unaffected by shunt resistance (FF₀) to the fill factor affected by shunt resistance (FF_SH) is:

FF_SH = FF₀(1 – 1/r_SH)

This equation is valid for r_SH > 0.4.

Source: Siliconvlsi

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