Hi, I am trying to find out series and shunt resistance of solar cell from I-V curve which starts from Isc and going to Voc. I read some papers and for single illumination mostly said Rs= -(dv/dI)V=Voc and Rsh= -(dv/dI)I=Isc. so I am finidng Rs from slope between points from Vmax to Voc, and Rsh from Isc to Vmax. Am I doing something wrong? My series resistance is coming very high around 11k ohm.