Electrostatics and Transport of dilute species

Hi all,

I am modelling a pn junction using the coupled electrostatic and transport of dilute species physics module for weeks now without any success. I followed the model in tutorial provided on comsol model gallery but encountered the following problems:
(1) I got an I-V plot for the model but when I plot current density as function of applied voltage, it gives 0 A/m^2 at any applied voltage which is strange.
(2) I do not fully understand the expression for cathode current (Ic) used in the tutorial. what does the Lagrange multipliers cn_lm and cp_lm do in Ic expression.
(3) After perturbing the system by including the generation term, I did not see any change in the I-V plot.
(4) Even when I set the recombination and generation term to zero, I still get I -V plot...I am confused about this.

Please, can someone help me out? I attached my file below.

Thanks