Cuprous/Cupric Heterojunction Photocathodes with Optimal Phase Transition Interface via Preferred Orientation and Precise Oxidation

Abstract

To effectively transport photogenerated charges within a cuprous oxide (Cu2O) photocathode and to transfer them to the electrolyte, cupric oxide (CuO) as a heterojunction material enable to provide the additional built-in electric field is perfectly suitable band position and can be produced from the original Cu2O films by simple oxidation process. However, their different crystal structures and lattice constants inevitably induce crystal distortions and the formation of a defective interface, resulting in the reduction of the photocurrent and photovoltage. To alleviate these intrinsic problems and improve its photoelectrochemical (PEC) performance, we fabricated a Cu2O/CuO interface with high crystallinity and a well-aligned atomic arrangement by preparing a Cu2O absorber underlying layer preferentially oriented with [111] direction and forming a thin CuO overlayer (20–30 nm) via oxidation process at precisely controlled reduced oxygen partial pressure. At 5 Torr, the resultant Cu2O double-layer structure exhibited smooth crystallographic phase transition boundary from cubic Cu2O to monoclinic CuO and well-aligned lattice fringes. This exhibited considerable improvement in photocurrent density (2.8 mA/cm2 at 0 V vs RHE) and onset potential (0.83 V), compared with those of pristine Cu2O. Importantly, these enhancements were achieved without coating of photocatalytic materials on the photoelectrodes.

Modification of large area Cu2O/CuO photocathode with CuS non-noble catalyst for improved photocurrent and stability

“…7 c). The typical semicircular feature of the Nyquist plot was found for all the three photoelectrodes, showing a progressive reduction in the semicircle diameter, associated with the charge transfer resistance (R ct ), passing from Cu 2 O to Cu 2 O/CuO and Cu 2 O/CuO/CuS heterostructures, confirming the staggered band alignment between Cu 2 O and CuO 17 , 18 , 24 and the catalytic activity of CuS 21 , 26 , 33 . The results are in agreement with the photoelectrochemical polarization tests where higher photocurrents were recorded for the CuS-modified surface.…”

“…Although the cuprous oxide film showed a relatively high immersion potential under the illumination + 0.62 V versus RHE, significant photocurrent density values (− 0.1 mA cm −2 ) are only recorded for potential lower than + 0.31 V versus RHE, while achieving a value of − 0.53 mA cm −2 at 0 V versus RHE. On the other hand, the Cu 2 O/CuO heterostructure showed a clear increase in the immersion potential under illumination (~ 90 mV) along with a more positive onset potential (+ 0.55 V vs RHE at − 0.1 mA cm −2 ) due to the formation of a staggered band structure 24 , improving the charge separation (Fig. 6 ).…”

Cu2O/CuO heterojunction catalysts through atmospheric pressure plasma induced defect passivation

“…These defects act as trapping sites for charge carriers, leading to degraded photocurrent and photovoltage values. [39] Till date Cu2O/CuO heterojunction has been synthesized using several methods such as sputtering [40], chemical vapor deposition [41], annealing [18], electrodeposition [21,39] and sol-gel approaches. [35] But all these techniques either need sophisticated vacuum equipment's or complex chemistry.…”

Optimal n-Type Al-Doped ZnO Overlayers for Charge Transport Enhancement in p-Type Cu2O Photocathodes

“…The use of the AA@AZO overlayer induces a relatively abrupt band bending at the Cu 2 O/AZO interface, which is expected to enhance charge transport because of the stronger built-in potential. The band structure of Cu 2 O has been described in a previous study [ 37 ].…”