How to Calculate the transfer function and plot it after making fourier transform in frequency domain in terms of magnitude and phase?

Hello everyone. I have a trouble of plotting the transfer function in terms of magnitude and phase after making the fourier transfer of two signals. First, I have used excel xlxs to read the column to plot in time domain and frequecny domain then I calculate the transfer function and this goes fine. But for magnitude and phase, I have trouble for plotting them. I tired to plot them, but this is totally incorrect. would someone help me with this? here is the code and excel file also

clear

solarcell1 = xlsread('solarcell.xlsx','A2:C100005');

t=solarcell1(:,1);

N=length(t);

Channel1V = solarcell1(:,2);

Channel2V = solarcell1(:,3);

sig1=Channel1V;

sig2=Channel2V;

fs=1/((solarcell1(3)-solarcell1(2))*1e-3);

FA1=fs/length(sig1);

FA2=fs/length(sig2);

frange1=-fs/2:FA1:fs/2-FA1;

frange2=-fs/2:FA2:fs/2-FA2;

subplot(3,2,1);

plot(t,sig1);

hold on

plot(t,sig2);

title('Input and Output of Solar cell');

xlabel('Time');ylabel('Amplitude');

subplot(3,2,2);

plot(t,sig2);

title('Output');

xlabel('Time');ylabel('Amplitude');

z1=fftshift(fft(sig1))/length(t);

subplot(3,2,3);

plot(frange1,abs(z1));

title('Input');

xlabel('Freq.');ylabel('Amplitude');

z2=fftshift(fft(sig2))/length(t);

subplot(3,2,4);

plot(frange2,abs(z2));

title('Output');

xlabel('Freq.');ylabel('Amplitude');

TFC=z2./z1;

magnitude=20*log(abs(TFC));

phase=atan2(imag(TFC),real(TFC));

subplot(3,2,5);

semilogx(frange1(1002:N),magnitude(1002:N));

title('Magnitude');

xlabel('Freq.');ylabel('Magnitude');

subplot(3,2,6);

semilogx(frange1(1002:N),phase(1002:N));

title('Phase');

xlabel('Freq.');ylabel('Phase');