**3.2. Working principle of QDSSC**

Basically, QDSSCs working mechanism is identical with DSSCs. TiO2 is used in the photoanode. Upon light incident, the QD sensitizers absorb photons to excite electrons into its CB (photoexcitation). Electrons in the CB of QDs will be injected to the CB of TiO2 and oxidized

QDs will be regenerated by receiving electron from 2 <sup>−</sup> ions in the electrolyte [69]. From CB of TiO2, electrons will leave the photoanode, enter the external circuit and reach the counter electrode where they will be received by <sup>2</sup> <sup>−</sup> ions in the electrolyte ( 2 − transforms into 2 <sup>−</sup>).

As the above process continues, electrons will keep moving through the cell and current is produced. **Figure 11** shows the working mechanism of QDSSCs where only electron movement is shown. Red arrows in **Figure 11** indicate the electron movement.

**Figure 11.** This figure demonstrates the movement of electron starting from QDs excited due to photon absorption.
