Stoichiometric Engineering of Cs₂AgBiBr₆ for Photomultiplication-Type Photodetectors

Photomultiplication (PM)-type photodetectors with a high external quantum efficiency (EQE) can be realized through adequately engineered trap states and trap-assisted charge injection. By strategically introducing slightly rich Bi and highly rich Br stoichiometric conditions, efficient trap states are realized for holes in lead-free Cs1.98AgBi1.15Br7.9 double perovskite (DP). With the diode structure of ITO/SnO2/Cs1.98AgBi1.15Br7.9/poly(3-hexylthiophene) (P3HT)/MoOx/Ag, where SnO2 and P3HT layers are used as the hole- and electron-blocking layers, respectively, successful realization of the selective hole trap and the resulting band bending/electron injection at the anode interface is demonstrated. As a result, a high EQE of ∼16,000%, responsivity of ∼50 A W–1, and specific detectivity of over 1012 Jones at −3 V are demonstrated. The origin of the suggested PM mechanism is discussed using photophysical and optoelectronic measurements and theoretical studies. This work ensures the successful demonstration of PM-type photodetectors using lead-free Cs2AgBiBr6 DP through strategic trap engineering.