To measure four quadrants characteristics, voltage and current sources are required in addition to voltage and current meters. Furthermore, since the harvested energy from IPV cells is small, a very accurate and sensitive measuring method is necessary. Therefore, the Agilent (Keysight) B2902A as a two channel precision Source/Measure Unit (SMU) with resolution of 100 fA and 100 nV is used. It connects to the IPV with a 4-wire connection setup as shown in Fig. 4 to eliminate the voltage error caused by the test leads residual resistance.