Reverse breakdown voltage setting for the diodes in a solar cell model in SPICE

Question

I want to simulate the reverse breakdown behavior of a two diode model solar cell in SPICE.
The diodes configurations without considering the breakdown voltage are as below:

.model diode d( Is=1.5e-10,  xti=3)
.model diode2 d(Is=1.77e-6, n=2, xti=3)

With the given diodes configurations, I can simulate all characteristics before the breakdown voltage point.
By adding the breakdown voltage point to the diode model, I cannot see the curve in forward bias anymore and it does not work properly.

.model diode d( Is=1.5e-10,  xti=3, vrev=15, BV=15)
.model diode2 d(Is=1.77e-6, n=2, xti=3, vrev=15, BV=15)

In short, when I add the code for reverse breakdown voltage point, my diode does not work properly in forward bias! Please help me with this problem.

Answer 1

From LTWiki:

There are two types of diodes available. One is a conduction region-wise linear model that yields a computationally light weight representation of an idealized diode.

...

This idealized model is used if any of Ron, Roff, Vfwd, Vrev or Rrev is specified in the model.

So when you included the VREV parameter, you changed your model to use the piecewise linear diode model instead of the usual nonlinear model. Your other parameters (IS, XTI, and BV) are ignored and the piecewise linear model parameters that you didn't specify take their default values.. This could make a substantial change to the operating behavior of the diodes in your model.