The Voc from the data and from the plot have very much different values in my case. The solar cell I am talking About is DSSC. So what value I should use in calculating efficiency?
You mean that you determined directly Voc from the simulator and you determined it from the measured IV curve. The value measured from the IV cure is more trusted as a real value as you as it is extracted under the correct definition for the quantity. It was me not clear how you calculate Voc by simulation.
The second matter is that you have to determine the fill factor, which can be extracted also from the I curve. Third, the short circuit can be also extracted from the IV cure and so all the parameters of the efficiency calculations will be all extracted from the same curve. The results will be more consistent.
However you have to make further investigations to get out the cause of the discrepancy between the the two open circuit voltage values.
Voc from simulator data means where tha current changes its sign from negative to positve, as Voc is open ckt votlage when current vanishes to zero. It can be seen from the txt data from simulator directly. But when I plot this data I get huge diffrence in Voc value.
okay, well now the matter is more clear. Would you please display the IV curve? .and also the numerical value of Voc from the simulator to get an insight on the problem.