Interfacial Engineering Determines Band Alignment and Steers Charge Separation and Recombination at an Inorganic Perovskite Quantum Dot/WS Junction: A Time Domain Ab Initio Study.

Using time-domain density functional theory and nonadiabatic (NA) molecular dynamics, we demonstrate that interfacial interaction between WS and CsPbBr quantum dots (QDs) determines the band alignment, leading to a type-II and type-I heterojunction for the WS contacting with Cs/Br- and PbBr-terminated facet QD, respectively. In the type-II heterojunction, electron transfer is faster than hole transfer arising due to the stronger NA coupling, higher density of electron acceptor states, and more and higher phonon modes involved. Both the electron and hole transfer times are subpicosecond, in agreement with experiments. The energy lost by the electron and hole is slower than charge transfer by several times, facilitating keeping charge carriers sufficiently "hot". Particularly, the electron-hole recombination occurs over 1 ns, favoring a long-lived charge-separated state. Detailed atomistic insights into the photoinduced charge and energy dynamics at the WS/QD interface provide valuable guidelines for improving performance of perovskite/transition-metal dichalcogenide solar cells.