Influence of stoichiometry on phase composition and crystal structure of compounds of the AgxCu1−xGaSe2 (0.0≤ x ≤1.0) system used to obtain photocathodes

The AgxCu1−xGaSe2 semiconductor compound is considered as one of the promising materials for creating photocathodes, which are used to generate hydrogen by photoelectrochemical (PEC) water splitting under solar radiation. In this paper, the effect of the silver and copper ratio in the AgxCu1−xGaSe2 system ( 0.0 ≤ x ≤ 1.0 ) on their phase composition, crystal structure and loss kinetics of photogenerated current carries is investigated using electron microscopy, X-ray diffraction, Raman spectroscopy and time-resolved microwave photoconductivity method. It is shown that the synthesized compounds of the AgxCu1−xGaSe2 system generally do not have deviations from stoichiometry for gallium and selenium, as well as for copper and silver for the edge compounds. However, in compounds with x in the range from 0.2 to 0.5 , there is a deviation of the mole fractions of silver ( x ) and, accordingly, copper from the technological ones, mainly at x = 0.3 and 0.4 , while for other values of x , no significant deviations were found. It has been established that the CuGaSe2 and AgGaSe2 edge compounds crystallized in a tetragonal structure of the chalcopyrite type and are single-phase. Whereas the compounds of the AgxCu1−xGaSe2 system at x < 0.3 and x > 0.6 form a solid solution and have a lattice matrix of theCuGaSe2 and AgGaSe2 type, respectively. And at x in the range of 0.3 – 0.6 , partial mixing of these phases occurs with the formation of solid solutions and phase splitting. The analysis of loss kinetics of photo-generated current carriers by the method of microwave photoconductivity showed that the longest lifetimes are characteristic for x = 0 and x = 1 . This is due to the large number of defects inAgxCu1−xGaSe2 , which are deep traps for photogenerated current carriers, compared to CuGaSe2 and AgGaSe2