Deciphering the Role of Quantum Dots Size in the Ultrafast Charge Carrier Dynamics at the Perovskite-Quantum Dots Interface

Abstract

Understanding the behaviour of electrons and holes (e, h) diffusion and transfer at the interfaces of photoexcited hybrid materials at different densities of photoexcited charge carriers is paramount to the development of efficient optoelectronic devices. Nanocomposites formed by methylammonium lead iodide perovskite (MAPbI3) and semiconductor colloidal quantum dots (QDs)are among these hybrid materials under intensive studies. However, the reciprocal influence of the components in the composite material on the temporal evolution of the photoinduced charge carriers is still poorly explored. This study explores the ultrafast temporal behaviour of the photoexcited charge carriers in MAPbI3/PbS QDs films, letting a special attention to the role of the PbS QD size. Armed with fs-time-resolved UV-VIS transient absorption and terahertz techniques, we unravel the effect of different sizes of PbS QDs, embedded in perovskite (PS) host matrix, on the processes of e and h diffusion, transfer to the QDs phase and recombination. While the decays are dominated by e and h transition from PS to QDs, the increase in the size of QDs results in an acceleration of the charge carriers transition processes represented by the total transition rate constants of electrons (ke) and holes (kh). The total ke and kh values change form 0.1and 1 (109 s-1) to 4.5and 22 (109 s-1), respectively. We extract the rate constants of their diffusions (kediff = 2.2 × 1010s-1 and khdiff = 1.1 × 1010 s-1) and transfers to the interfaces (ket = 0.1 to 1.6 × 1010 s-1 and kht = 0.1 to 0.8 × 1010 s-1). Furthermore, the analysis of spectral behavior of PS and PS/QDs upon pumping with different fs-laser fluences indicate the presence and photoformation of excitonic states. The acceleration of such processes decreases the contribution of undesirable charge carriers trapping and non-radiative recombination within PS.