Identifying Reactive Sites and Surface Traps in Chalcopyrite Photocathodes

Abstract

Gathering information on the atomic nature of reactive sites and trap states is key to fine tuning catalysis and suppressing deleterious surface voltage losses in photoelectrochemical technologies. Here, spectroelectrochemical and computational methods were combined to investigate a model photocathode from the promising chalcopyrite family: CuIn0.3Ga0.7S2. We found that voltage losses are linked to traps induced by surface Ga and In vacancies, whereas operando Raman spectroscopy revealed that catalysis occurred at Ga, In, and S sites. This study allows establishing a bridge between the chalcopyrite's performance and its surface's chemistry, where avoiding formation of Ga and In vacancies is crucial for achieving high activity.

Photoelectrochemical CO2 Reduction at a Direct CuInGaS2/Electrolyte Junction

“…19 It is likely that these energy traps, induced by surface vacancies of In and Ga, are responsible for the FLP observed during the PEC CO 2 reduction. Finally, we can use the IMPS data to compare the relative magnitudes of the rate constants for the HER (in aqueous electrolyte 19 ) and the CO 2 -to-CO conversion. We note that although the rate constants obtained by IMPS are phenomenological, a qualitative comparison could be drawn given that the electrodes and experimental parameters are maintained and only the solvent and the reaction are altered.…”

Effect of charge selective contacts on the quasi Fermi level splitting of CuGa3Se5 thin film photocathodes for hydrogen evolution and methylviologen reduction

“…In both MV and NaPi electrolytes, E F,p becomes more oxidizing with increasing light intensity, as expected for a photocathode. On the other hand, E F,n stays constant and remains close to the energy of the surface states (likely gallium vacancies 16 ), approximately 0.5 eV above the valence band edge. This phenomenon is known as Fermi level pinning and has been documented for many semiconductor electrodes, 16,43,[52][53][54][55] incl.…”

“…On the other hand, E F,n stays constant and remains close to the energy of the surface states (likely gallium vacancies 16 ), approximately 0.5 eV above the valence band edge. This phenomenon is known as Fermi level pinning and has been documented for many semiconductor electrodes, 16,43,52–55 incl. chalcopyrites.…”

“…14 However, the photovoltage of CuGa 3 Se 5 photocathodes (0.2 V, which corresponds to only 11% of the band gap) continues to be very low 13,14 The Sivula group reported that photovoltage losses in the related CuIn 0.3 Ga 0.7 S 2 photocathode are caused by surface Ga and In vacancies. 16 Similar surface defects may limit the operation of the CuGa 3 Se 5 (CGSe) photocathode. Indeed, it has been shown that surface treatment with CdS boosts proton reduction with copper and silver chalcopyrites.…”

Operational Spectroelectrochemical Investigation on the Interfacial Charge Dynamics of Copper Bismuth Oxide Based Photocathode

“…Alternatively, as another powerful frequency dominant technology, IMPS is used to decouple the process of charge transfer and recombination at the electrode–electrolyte interface under modulated illumination . To date, it is rare to see the discussion about the surface states in semiconductors of IMPS research, although this is a bottleneck problem that restricts the PEC performance, and existing reports are limited to typical photoanode materials such as TiO 2 and BiVO 4 . , Considering that the existence of surface states in CBO photocathodes has been previously proven, a dynamic model including the surface-state capacitance is used to quantitatively describe the interface charge behavior. Figure panels a–c show the above-mentioned dynamic mechanism.…”