Unravelling the Underlying Hot Carrier Transfer and Relaxation Pathways in Type-1 CsPbBr3-PbS System

The scientific community around the globe has developed a great deal of interest in heterojunction devices based on the conjunction of perovskite and other semiconducting materials due to the extensive range of properties demonstrated by them. Among the various probable combinations, the CsPbBr3 and PbS heterostructure system by now has proved itself as a strong contender for usage in phototransistor applications. This heterosystem has already demonstrated its dominance over the individual constituting systems in terms of superior photoresponsivity and broader response width. However, it lacks an in-depth investigation of the fundamental dynamics that can elucidate the ground for such efficient behavior. For this purpose, here we have used femtosecond broadband transient absorption (TA) spectroscopy employing energetically distinct pump excitations (300, 480, and 620 nm) to elaborately understand the essential interplay between the native carrier relaxation and the carrier transfer mechanisms in this interesting CsPbBr3/PbS Type-1 architecture. Such a careful choice of different pump excitations has been made to obtain the photogenerated carriers in differently densed energy states of CsPbBr3 and PbS. Consequentially, it was observed that the hot carrier transfer process tends to be bidirectional (from CsPbBr3 to PbS and vice versa) when the photogeneration takes place in the hot states (300 nm). On the contrary, it was however found that for the instance of close to band edge excitation w.r.t. CsPbBr3 band edge (480 nm), the transfer of carriers occurs merely in one direction, that is, from CsPbBr3 to PbS states. This detailed investigation thus provides an opportunity to understand the competition between two processes whose interplay is strongly dependent on the initial energy of the carriers and the density of states in which the carriers are initially excited.

Automated summary

There is a significant interest in heterojunction devices based on perovskite and other semiconducting materials within the global scientific community, with the CsPbBr3 and PbS system showing potential for phototransistor applications. By using femtosecond broadband transient absorption spectroscopy, the investigation into carrier transfer mechanisms in the CsPbBr3/PbS architecture revealed bidirectional or unidirectional carrier transfer behaviors depending on the density energy states of the carriers.