Simulation options

The Options tab contains the top-level simulation settings that determine the scope and detail of the calculation. These settings affect which inputs are available on other tabs and which outputs are produced.

Device configuration

The device configuration determines the scope of the simulation. Four options are available:

Solar cell: There is no spacing between cells, irrespective of the wafer shape. The structure can have multiple layers (e.g., glass, EVA, silicon). The electrical model solves for a single solar cell.
Unit-cell module: The ray tracing solves a single unit cell. Spacing between cells can be included but frames cannot. If the edge condition (see below) is set to “100% reflectance” then solving a unit-cell module is equivalent to solving an infinitely large module for which the optical behaviour of all cells is identical. Modifying the number of cells in the module affects the electrical behaviour but not the optical behaviour.
Module: A full module is simulated. Spacing between cells and frames can be included. Modifying the number of cells in the module affects both the optical and electrical behaviour. The ray tracing determines the generation current in each cell, and a SPICE circuit simulation determines the resulting electrical behaviour. This electrical solver takes into account the non-uniform generation current and hence the “electrical mismatch”.
System: A system comprised of one or more modules is simulated. See system configuration for more information.

Use “unit-cell module” if you want to simulate a module without frames and you are not interested in electrical mismatch. You can then use fewer rays to determine the electrical behaviour of the module. (Electrical mismatch will be negligible for most module designs under standard illumination conditions.)

Use “module” if you want to simulate a module with frames and/or you want to account for electrical mismatch. Be sure to simulate with a sufficient number of rays to minimise electrical mismatch due to the stochastic nature of ray tracing — increase the number of rays until the mismatch loss (provided on the JV output tab) converges to a desired resolution.

Additional calculations

These optional solvers generate additional outputs when enabled. Enabling them increases simulation time.

Enable electrical solver: Activates the SPICE circuit solver to compute IV curves, power output, and mismatch losses. Required for any electrical output.
Enable electrical modifiers: Allows modifiers to be applied to individual cells or groups of cells, enabling modelling of partial shading, degradation, or manufacturing variations. Only available when the electrical solver is enabled and the device configuration is set to a module-based option.
Enable colour solver: Computes the average colour of the illuminated area.
Generation profiles: Computes the depth-resolved generation profile in the cell (and films if desired). Additional inputs for the generation profile appear below the checkbox when enabled.
Include detector: Enables an optical detector that registers rays within user-defined acceptance angles.
Solve for Quokka3: Creates an input file compatible with Quokka3.

Advanced options

Absorption in each film: Computes the absorption in each individual film within a stack of films. This is always enabled.
Include FCA: Enables the option to include free-carrier absorption (FCA) in any layer.
Variable film thickness: Enables the option to define a spatially varying thickness for any film.

Ray tracer settings

These settings control the ray tracing engine. Default values are suitable for most simulations.

Rays per run: The total number of rays to trace. More rays reduce the statistical noise in results but increase simulation time.
Trace polarisation: Selects how ray polarisation is handled during tracing.

Additional settings are available under Show advanced options:

Rays per packet: The number of rays traced per computational packet.
Max bounces per ray: The maximum number of reflections a ray can undergo before being terminated.
Intensity threshold: Rays with intensity below this threshold are terminated.

Spectral range

Defines the wavelength range and resolution for the ray tracing simulation:

Minimum wavelength: The shortest wavelength to trace.
Maximum wavelength: The longest wavelength to trace.
Wavelength interval: The spacing between wavelength bins.

Simulation boundary

The edge interface setting determines what happens when rays reach the vertical edges of the simulation structure. Two options are available:

Ideal absorber (100% absorptance): Any rays that intersect the edge of the simulation are absorbed and do not return. This setting is used to simulate a module with a finite number of cells, where light that reaches the module edge is lost.
Ideal reflector (100% reflectance): Any rays that intersect the edge of the simulation are specularly reflected without any change to their intensity. This setting is used to simulate a module with infinitely many solar cells — a unit-cell module with this option is optically equivalent to an infinite array of identical cells.

Quokka3 settings

When Solve for Quokka3 is enabled, additional settings appear for configuring the Quokka3 output. The recommended way to use SunSolve results in Quokka3 is with a *.sun file. Once SunSolve has run, the *.sun file can be downloaded using Export outputs → SunSolve for Quokka3.

The Solve type dropdown provides four options. For bifacial options, a sweep is used which doubles the number of rays consumed by the simulation.

Text-Z (monofacial): Applies a single, normally incident light source and solves the front-side optics only. Generation mode in Quokka uses the “Text-Z” model.
Text-Z (bifacial): Applies a normally incident light source and solves once for the front-side and once for the rear-side. Generation mode in Quokka uses the “Text-Z” model.
Generation profile (arbitrary irradiance): Any type and number of light sources may be defined. Generation mode in Quokka uses the “defined-generation” model.
Generation profile (bifacial analysis): Applies a normally incident light source and solves once for the front-side and once for the rear-side. Generation mode in Quokka uses the “defined-generation” model.

Options (1) and (2) solve the spectrally resolved cell optics in SunSolve with illumination defined in Quokka3, which limits the available light source settings within SunSolve. Options (3) and (4) require the light source within Quokka3 to match exactly the light source defined in SunSolve, allowing arbitrary light source configurations. Options (3) and (4) are available to advanced users only.

Users can also use the Quokka3 solve option to export the optical pathlength enhancement (z) versus wavelength. Use solve type (1) or (2), then select the “Optical pathlength enhancement (z)” option in the export outputs window.