3.5 Specifying voltage and generation rates in transient simulations
\(\mathtt{\require{color}{\color[rgb]{0.000000000000000,0.500000000000000,0.500000000000000} ZimT}}\) requires a file (\(\mathtt{\require{color}{\color[rgb]{0.000000000000000,0.500000000000000,0.500000000000000} tVGFile}}\)) to specify which times, external voltages 1 and relative generation rates \(\mathtt{\require{color}{\color[rgb]{0.000000000000000,0.500000000000000,0.500000000000000} G\_ frac}}\)) should be simulated. In addtion, there must a column called \(\mathtt{\require{color}{\color[rgb]{0.000000000000000,0.500000000000000,0.500000000000000} Track}}\), see section 3.6.
This file must contain the correct header and may contain comments. For example:
*You could put a brief explanation about what this file does. *Fully optional though. t Vext G_frac Track comments 0 0 1 0 no comments! 1e-3 0.1 1 0 more voltage! 2e-3 0.1 1 0 3e-3 0.1 1.1 0 a bit more light 4e-3 oc 2 0 now try to find Voc.
The comments are optional and \(\mathtt{\require{color}{\color[rgb]{0.000000000000000,0.500000000000000,0.500000000000000} ZimT}}\) ignores them but the \(\mathtt{\require{color}{\color[rgb]{0.000000000000000,0.500000000000000,0.500000000000000} t}}\) \(\mathtt{\require{color}{\color[rgb]{0.000000000000000,0.500000000000000,0.500000000000000} Vext}}\) \(\mathtt{\require{color}{\color[rgb]{0.000000000000000,0.500000000000000,0.500000000000000} G\_ frac}}\) \(\mathtt{\require{color}{\color[rgb]{0.000000000000000,0.500000000000000,0.500000000000000} Track}}\) part is mandatory and this should not be preceded by any other characters on that line. If \(\mathtt{\require{color}{\color[rgb]{0.000000000000000,0.500000000000000,0.500000000000000} ZimT}}\) cannot find these characters (white space is ignored, not case-sensitive) it stops. The first time should be 0 as this corresponds to a steady-state condition at the start of the simulation. Time and voltage are in SI units, so seconds and volts. \(\mathtt{\require{color}{\color[rgb]{0.000000000000000,0.500000000000000,0.500000000000000} G\_ frac}}\) is the fractional generation rate. The total rate of electron hole pairs is the product of the calculated profile—if using the transfer matrix algorithm—or the \(\mathtt{\require{color}{\color[rgb]{0.000000000000000,0.500000000000000,0.500000000000000} G\_ ehp}}\) of the respective layers. \(\mathtt{\require{color}{\color[rgb]{0.000000000000000,0.500000000000000,0.500000000000000} Track}}\) can only be 0 (which is typical), or 1.
In order to simulate a transient photovoltage experiment, or just an open-circuit, the voltage may be specified as \(\mathtt{\require{color}{\color[rgb]{0.000000000000000,0.500000000000000,0.500000000000000} oc}}\)—for open-circuit. \(\mathtt{\require{color}{\color[rgb]{0.000000000000000,0.500000000000000,0.500000000000000} ZimT}}\) will then solve for the correct applied voltage such that the current density is close to zero.
\(\mathtt{\require{color}{\color[rgb]{0.000000000000000,0.500000000000000,0.500000000000000} ZimT}}\) reads this file, calculates a time step, reads another line, etc. \(\mathtt{\require{color}{\color[rgb]{0.000000000000000,0.500000000000000,0.500000000000000} ZimT}}\) can also be used to do a steady-state voltage sweep, just like \(\mathtt{\require{color}{\color[rgb]{0.000000000000000,0.500000000000000,0.500000000000000} SimSS}}\) by simply putting all times to 0. 2 While it is not possible to go back in time, it is possible to go back to the steady-state condition (\(t\)=0).