Improving Optoelectronic Properties of Ternary Silver Chlorides via Defect Engineering

Ternary silver chlorides are highly intriguing due to their distinctive broad emission and large Stokes shift, endowing them as promising candidates for optoelectronic applications. However, practical applications of these materials are seriously hindered by their inferior luminescence efficiency. In this work, to illustrate the underlying microscopic mechanism for these disadvantages in ternary silver chlorides, taking the layer CsAgCl2 and chain Cs2AgCl3 as typical examples, we investigated the defect and excitonic properties with first-principles calculations combined with experiments. Our results suggest that chlorine vacancies are dominant defects that exhibit low formation energies and create deep energy levels in the band gaps. Moreover, the calculated emission energies (1.85 and 2.35 eV for CsAgCl2 and Cs2AgCl3) of the excitons trapped by the chlorine vacancies (VCl) are in line with the main PL peaks observed in the experiment. Due to the deep energy levels, the chlorine vacancy could serve as a trap center for photocarriers, resulting in poor optoelectronic properties. It is predicted that synthesizing p-type compounds in chlorine-rich conditions can reduce the chlorine vacancy concentration on the layer surface for CsAgCl2 and the chain surface for Cs2AgCl3 and thus significantly improve their optoelectronic properties.