Fig. 2: Cross-sectional morphology of ETL coated FTO.

a SEM cross-sectional image of c-SnO2-coated FTO (left) and SnO2 QDs-coated FTO (right). HAADF-STEM cross-sectional image (left) and zoom-in image of the selected area (right) of b c-SnO2-coated FTO and c SnO2 QDs-coated FTO. HAADE-STEM-EELS cross-sectional element mapping of d c-SnO2-coated FTO and e SnO2 QDs-coated FTO