Figure 7
From: Photocapacitive CdS/WOx nanostructures for solar energy storage
Proposed band structure of the CdS/WOx composite, constructed using energy estimates from XPS, UPS and UV-Vis diffuse reflectance measurements. A potential offset of 0.5 eV has been assumed between the Fermi levels of CdS and WOx, denoted EF(CdS) and EF(WOx), respectively, in accordance with the XPS measurements in Figs 4, 5; it should be recognised that these values are not representative of the material in other electronic environments, but are nevertheless instructive for qualitative determination of the relative energy band edge positions. Based on the plotted estimates, an energy difference of approximately 1.4 eV is predicted to have existed between the conduction band minima of CdS, ECB(CdS), and WOx, ECB(WOx), which indicates that the inter-component transfer and subsequent trapping of photoexcited electrons was thermodynamically viable. The trapping of photoexcited electrons and their contribution to photocurrent was likely facilitated by the quenching of photoinduced holes by electrons from the valence band of WOx, as shown.
