The electron lifetime measurement of solar cells by using open circuit voltage decay (OCVD) is an interesting study to analyze recombination behavior at q-dot electrolyte interface. The OCVD spectra of 1PbS/1CdS, 1PbS/2CdS and 1PbS/3CdS are shown in Fig. 3a while OCVD spectra of 1PbS/3CdS, 2PbS/3CdS and 3PbS/3CdS shown in Fig. 3b. From the OCVD measurements, the lifetimes of electrons were calculated by using the Eq. (1)[20].