Your question is ambiguous. Your question is about what is the model that Mathworks used in building its block? or about if a model is found in Matlab?
If the second, yes there is a model for PV or solar cell, and if the first the model is 2 diode model. you can read more in Mathworks site help: http://www.mathworks.com/help/physmod/elec/ref/solarcell.html