In order to get a deeper understanding of the conduction mechanisms limiting the electrical characteristics of ITO/PEDOT:PSS/P3HT:PCBM/Al solar cells, dark current-voltage measurements at different temperatures were analyzed using a compact electrical equivalent circuit previously used in p/n junctions. Between 0.2 V and 0.6 V, the current-voltage characteristic is modeled by an exponential term which can be described by Multi-Tunneling Capture Emission process. For larger voltage, the model takes into account Space-Charge Limited process and series resistance. In addition, the model is useful to calculate the built in potential of the solar cell using only dark current-voltage-temperature measurements.