Photoinduced Ultrafast Electron Transfer and Charge Transport in a PbI₂/C₆₀ Heterojunction

Abstract

Charge transport and electron transfer in a PbI2/C60 heterojunction were investigated. The charge carrier mobilities and trap densities of PbI2 were extracted from current–voltage characteristics of hole- and electron-only devices. Femtosecond transient absorption spectroscopy was used to elucidate the photophysical processes occurring in the heterojunction. For a pristine PbI2 film, trap-limited bimolecular recombination was the dominant mechanism in the case of low pump fluence. We observed photoinduced ultrafast electron transfer from PbI2 to C60 with a rate constant of 0.45 ps–1. Semiclassical Marcus electron transfer theory was used to estimate the electronic coupling between the conduction band edge of PbI2 and the lowest unoccupied molecular orbital of C60. We also fabricated a solar cell using the PbI2/C60 heterojunction. Electron transfer and charge extract efficiencies in our cell were also deduced. The performance-limiting factors for solar cells based on PbI2 were discussed and a strategy to improve the device performance was developed. Our work is useful for ultraviolet-harvesting transparent solar cells and other photophysical and photochemical applications.

Collective effects in photoionization of sodium clusters: plasmon resonance spill, induced attractive force and correlation minimum

“…Even though the corresponding branching ratio is unknown, we note the following: (i) the direct ionization, that provides the smooth background contribution of the TDLDA results, is known to be a much faster process (in attoseconds) for clusters [35,36]. (ii) In contrast, the thermalization/evaporation processes, that include ionic vibration, take far longer times (in femtoseconds) [37,38]. Therefore, it is conceivable that the dominant contribution to the measured absorption data above the ionization threshold energy is from the ionization process-the process that can quickly utilize the energy absorbed.…”

Virtual Issue on Ultrafast Charge Separation in Energy Research

“…18 Low reorganization energy, high electronic coupling, and high electron transfer efficiency between the donor and acceptor was reported for a PbI 2 /fullerene heterojunction, which promises enhanced solar cell performance. 19 The role of resonance between the triplet exciton and interfacial CS state leading to dissociation of the triplet exciton was demonstrated for the pentacene/TiO 2 D/A interface. 20 However, poor harvesting of energy can occur if the CT assembly has the same band gap as the donor.…”

“…The way in which aggregation of the donor polymer influences excited state photoprocesses in D/A blends was explored in detail for fullerene and nonfullerene acceptors by Chung et al Ultrafast energy transfer in a series of poly­(phenylene ethynylene) (PPE) polymers end-capped with thiophene–benzothiadiazole (TBT) showed the presence of exciton migration along the polymer chain . Low reorganization energy, high electronic coupling, and high electron transfer efficiency between the donor and acceptor was reported for a PbI 2 /fullerene heterojunction, which promises enhanced solar cell performance . The role of resonance between the triplet exciton and interfacial CS state leading to dissociation of the triplet exciton was demonstrated for the pentacene/TiO 2 D/A interface .…”