*3.1.3. Counter electrode*

The counter electrode is another important component in QDSSCs. Electrons from the photoanode are returned to the QD when the electrons react with the redox ions in the electrolyte. In DSSCs, platinum (Pt) is the best material to be used as the CE due to its high stability and high catalytic activity for the triiodide ion to be reduced into the iodide ion. However, Pt CE does not work for QDSSCs. This is because Pt [67]:


Hence, researchers look for alternative materials to be used as the CE such as noble metals, carbon based materials and metal chalcogenides [68]. The highest efficiency are presently exhibited by QDSSCs utilizing copper sulphide (Cu2S) as the CE (*η* = 9%) [39].
