In order to model the DSSC solar cell sing the hereojunction model you have to build the layer correspondence between the two types of cells. That is you can start with cathode material it is fto for example. Then it is followed by TiO2 compact layer after that comes the TiO2 scaffold layer on which the photosensitive die is deposited and then comes the electrolyte and metal. Both electrolyte and metal can be modeled by a hole transport layer and a metal layer.
You can refine such arrangement and collect the properties of each layer from the literature.