Matlab solar cell simulation

Using a default value of 0.2 for maximum step size. The simulation step size will be equal to or less than this value. You can disable this diagnostic by setting 'Automatic solver parameter selection' diagnostic to 'none' in the Diagnostics page of the configuration parameters dialog

how to solve this error

[Sargondjani]

This does not seem to be an error, but a warning, which you can ignore.