Understanding processes that contribute to efficiency losses during long-term operation of perovskite solar cells is crucial for achieving operational stability. Although maximum power point tracking...

Controlling charge transfer at the semiconductor-acceptor molecule interface is important for improving the performance of semiconductor assisted photocatalytic processes. The difference between the band energies of the semiconductor and the redox potential of the acceptor is known to control the kinetics of charge transfer. By employing p-phenylenediamine (PPD) and m-phenylenediamine (MPD) as probe molecules, we have systematically probed the hole transfer from excited perovskite nanocrystals of different bandgaps. The valence band energy of the donor mixed halide perovskite nanocrystal, which varied from 1.74 to 0.94 V vs NHE through halide composition, viz., varying Cl:Br and Br:I ratio, allowed us to change the driving force (−ΔG) of hole transfer. The rate constant of hole transfer as determined from the transient absorption and photoluminescence decay measurements showed a nonlinear dependence on −ΔG. Analysis of this dependence followed Marcus-electron transfer theory with a reorganization energy of ∼1 eV. Relatively higher reorganization energy as compared to pure solvent showed the ligand shell (oleylamine) and charged nanocrystal lattice playing a major role in the interfacial charge transfer processes. The energy dependence of the charge transfer rate constant provides new insights into the photocatalytic properties of perovskite nanocrystals and ways to maximize the charge transfer yield through bandgap engineering of the semiconductor.

Understanding charge carrier dynamics in two-dimensional (2D) semiconductors and their heterostructures is crucial for advancing their application in optoelectronic devices. In this work, two differen...

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ConspectusPhotoinduced energy and electron transfer processes offer a convenient way to convert light energy into electrical or chemical energy. These processes remain the basis of operation of thin f...

Control of forward and back electron transfer processes in semiconductor nanocrystals is important to maximize charge separation for photocatalytic reduction/oxidation processes. By employing methyl viologen as the electron acceptor, we have succeeded in mapping the electron transfer from excited CsPbI3 nanocrystals to viologen as well as the hole trapping process. The electron transfer to viologen is an ultrafast process (ket = 2 × 1010 s–1) and results in the formation of extended charge separation as electrons are trapped at surface-bound viologen sites and holes at iodide sites. The I2─• formation, which is confirmed through the transient absorption at 750 nm, provides a convenient way to probe trapped holes and its participation in the back electron transfer process. By employing a series of mixed halide compositions, we were able to tune the bandgap and valence band energy of the perovskite donor. The back electron transfer rate constant (kbet = 1.3–2.6 × 107 s–1) is nearly three orders of magnitude smaller than that of forward electron transfer, thus extending the lifetime of the charge-separated state. The weak dependence of the back electron transfer rate constant on the valence band energy suggests that trapping of holes at halide (I or Br) sites is involved in the back electron transfer process. The ability to extend the lifetime of the charge-separated pair can offer new strategies to improve the redox properties of semiconductor-based photocatalytic systems.