Comparative Study of Photocarrier Dynamics in CVD-deposited CuWO₄, CuO, and WO₃ Thin Films for Photoelectrocatalysis

Abstract

The temporal evolution of photogenerated carriers in CuWO4, CuO and WO3 thin films deposited via a direct chemical vapor deposition approach was studied using time-resolved microwave conductivity and terahertz spectroscopy to obtain the photocarrier lifetime, mobility and diffusion length. The carrier transport properties of the films prepared by varying the copper-to-tungsten stoichiometry were compared and the results related to the performance of the compositions built into respective photoelectrochemical cells. Superior carrier mobility was observed for CuWO4 under frontside illumination.

Characterization of Cu2O/CuO heterostructure photocathode by tailoring CuO thickness for photoelectrochemical water splitting

“…To hand, the annealing time of 20 min produces the optimal CuO thickness enough to fully spread the space charge region out, showing the enhanced band bending. In addition, the CuO thickness (90 nm) in this case coincides with the minority carrier diffusion length of CuO ($100 nm), [21][22][23] resulting in the efficient charge transport. However, in the long annealing time over 20 min, the CuO thickness is much thicker than the minority carrier diffusion length of CuO.…”

“…In addition, it hinders the efficient charge transport in the CuO layer because it has a short carrier diffusion length (10-200 nm). [21][22][23]…”

“…In addition, it hinders the efficient charge transport in the CuO layer because it has a short carrier diffusion length (10–200 nm). 21–23 Therefore, it is significant to control the CuO thickness in the Cu 2 O/CuO heterostructure for the optimal PEC performance of Cu 2 O/CuO heterostructure (Cu 2 O/CuO) photocathode.…”

Femtosecond Charge Density Modulations in Photoexcited CuWO4

“… 10 − 14 However, the origin of charge carriers and their behavior in CuWO 4 are not well understood due to the scarcity of the experimental studies that probe the relaxation dynamics of the optically excited Cu electronic states, particularly in the fs/ps time domain. 15 , 16 Therefore, we believe that understanding the ultrafast electronic transitions in CuWO 4 in this time domain could provide a clearer insight on the nature of the electronic structure of CuWO 4 , which is highly debatable in literature 8 , 10 , 11 , 14 , 17 …”

“…It is known as an n-type semiconductor and its valence band is believed to be composed mainly of oxygen 2p states that are hybridized with tungsten and copper s, p, and d states. , The conduction band contains mainly W 5d states hybridized with the oxygen 2p states. In addition, it has been claimed that the single Cu 3d hole contributes to the bottom of the conduction band, which shifts the conduction band minimum in CuWO 4 downward compared to WO 3 . − However, the origin of charge carriers and their behavior in CuWO 4 are not well understood due to the scarcity of the experimental studies that probe the relaxation dynamics of the optically excited Cu electronic states, particularly in the fs/ps time domain. , Therefore, we believe that understanding the ultrafast electronic transitions in CuWO 4 in this time domain could provide a clearer insight on the nature of the electronic structure of CuWO 4 , which is highly debatable in literature ,,,, …”