Equivalent circuit parameters

This page provides a complete reference of the parameters used in the SunSolve Power equivalent circuit model. Each parameter is listed with its symbol, units, valid range, and default value as configured in SunSolve.

All current densities are entered per unit cell area (A/cm²) and all specific resistances are entered in Ω·cm². SunSolve scales these internally by the cell area during simulation. See the current density vs. current notation section for details.

Light-generated current

ParameterSymbolUnitsMinMaxDefaultDescriptionLight-generated current density, $J_L$, A/cm², 0.00001, 0.1, 0.038, Photocurrent density generated by light absorption in the cell

First diode

The first diode is the primary component of the equivalent circuit and is required in all configurations.

ParameterSymbolUnitsMinMaxDefaultDescriptionSaturation current density 1, $J_{01}$, A/cm², 1×10⁻³⁰, 0.1, 1×10⁻¹², Saturation current density of the primary diodeIdeality factor 1, $m_1$, —, 0.1, 100, 1, Diode ideality factor for the primary diode

Second diode

The second diode is optional and is typically used to represent space-charge region recombination.

ParameterSymbolUnitsMinMaxDefaultDescriptionSaturation current density 2, $J_{02}$, A/cm², 1×10⁻³⁰, 0.1, 1×10⁻⁹, Saturation current density of the second diodeIdeality factor 2, $m_2$, —, 0.1, 100, 2, Diode ideality factor for the second diode

Resistive-limited enhanced recombination component

This optional component includes its own diode and series resistance. It can improve fitting accuracy for complex IV curve behaviour.

ParameterSymbolUnitsMinMaxDefaultDescriptionSaturation current density H, $J_{0H}$, A/cm², 1×10⁻³⁰, 0.1, 1×10⁻¹⁰, Saturation current density of the enhanced recombination diodeIdeality factor H, $m_H$, —, 0.1, 100, 1, Diode ideality factor for the enhanced recombination diodeSeries resistance H, $R_H$, Ω·cm², 0, 10¹², 1000, Series resistance in the enhanced recombination branch

Series and shunt resistance

ParameterSymbolUnitsMinMaxDefaultDescriptionSeries resistance, $R_s$, Ω·cm², 0, 10¹², 1.2, Total series resistance including bulk semiconductor resistance and contact resistance. See Series resistance calculation for how this can be computed from electrode geometry.Shunt resistance, $R_{sh}$, Ω·cm², 0, 10¹², 10000, Leakage resistance representing current paths that bypass the p-n junction

Additional component for thin-film cells

These parameters are used by the optional loss component which is primarily used for thin-film technologies such as a-Si:H and CdTe.

ParameterSymbolUnitsMinMaxDefaultDescriptionMobility-lifetime parameter, $d_i^2 / (\mu \tau_{\text{eff}})$, V, 0.000001, 2.0, 0.005, Combined material parameter representing the i-layer thickness squared divided by the effective minority carrier mobility-lifetime productBuilt-in voltage, $V_{bi}$, V, 0.1, 2.0, 0.9, Built-in voltage of the p-n junction used in the recombination loss calculation

Reverse bias breakdown

Each diode in the equivalent circuit can optionally include reverse bias breakdown behaviour. When enabled on a given diode, that diode exhibits a sharp increase in reverse current when the cell voltage drops below its breakdown voltage. Breakdown is disabled by default on all diodes.

This component is particularly relevant for module-level simulations involving partial shading, where individual cells may be driven into reverse bias by the current produced by the remaining unshaded cells.

Since the diodes are connected in parallel, the overall cell breakdown is governed by whichever enabled diode has the lowest breakdown voltage. For tandem devices with series-connected cells, the total breakdown voltage is the sum of the individual cell breakdown voltages.

First diode breakdown

ParameterSymbolUnitsMinMaxDefaultDescriptionBreakdown voltage, $V_{B1}$, V, 0, 1000, 15, Reverse voltage at which avalanche breakdown occurs in the first diode. This is an area-independent quantity.Breakdown current density, $J_{B1}$, A/cm², 1×10⁻³⁰, 1, 1×10⁻⁵, Current density at the breakdown voltage. Used during initialisation to calibrate $V_{B1}$ so that the reverse current matches $I_{B1} = J_{B1} \times A_{\text{cell}}$ at the onset of breakdown.

Second diode breakdown

ParameterSymbolUnitsMinMaxDefaultDescriptionBreakdown voltage, $V_{B2}$, V, 0, 1000, 15, Reverse voltage at which avalanche breakdown occurs in the second diode. This is an area-independent quantity.Breakdown current density, $J_{B2}$, A/cm², 1×10⁻³⁰, 1, 1×10⁻⁵, Current density at the breakdown voltage for the second diode.

Enhanced recombination diode breakdown

ParameterSymbolUnitsMinMaxDefaultDescriptionBreakdown voltage, $V_{BH}$, V, 0, 1000, 15, Reverse voltage at which avalanche breakdown occurs in the enhanced recombination diode. This is an area-independent quantity.Breakdown current density, $J_{BH}$, A/cm², 1×10⁻³⁰, 1, 1×10⁻⁵, Current density at the breakdown voltage for the enhanced recombination diode.