How to use fitoptions

%define thermal voltage at room temperature

global kT Sun filename x

x=x(:,1) y=y(:,1)

kT=25.85e-3

fo=fitoptions('Method', 'NonlinearLeastSquares','Lower',[0 0 1 0 0],'Upper',[2 2 2 3000 30]);

ft2 = fittype('lambertsolar2(x, R_s, R_p, N, I_0, I_p)','options',fo)

'Startpoint',[20,2000,1.6,1e-6,1e-3]

solarfit= fit(x,y,ft2)

I was trying to fit a data called x and y onto a function called lambertsolar2. However, It would give me an error like

??? No appropriate method, property, or field startpoint for class curvefit.llsqoptions.

Error in ==> fit at 319 start = options.startpoint;

Error in ==> run2 at 23 solarfit= fit(x,y,ft2)

Any suggestions on how to fix this?

Thank you!