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Abstract
Charge transport in three-dimensional metal-halide perovskite semiconductors is due to a complex combination of ionic and electronic contributions, and its study is particularly relevant in light of their successful applications in photovoltaics as well as other opto- and microelectronic applications. Interestingly, the observation of field effect at room temperature in transistors based on solution-processed, polycrystalline, three-dimensional perovskite thin films has been elusive. In this work, we study the time-dependent electrical characteristics of field-effect transistors based on the model methylammonium lead iodide semiconductor and observe the drastic variations in output current, and therefore of apparent charge carrier mobility, as a function of the applied gate pulse duration. We infer this behavior to the accumulation of ions at the grain boundaries, which hamper the transport of carriers across the FET channel. This study reveals the dynamic nature of the field effect in solution-processed metal-halide perovskites and offers an investigation methodology useful to characterize charge carrier transport in such emerging semiconductors.
Highlights
Three-dimensional metal-halide perovskite semiconductors have shown tremendous performance in optoelectronic devices, with solar cells achieving laboratory power conversion efficiencies above 25%.1,2 Owing to their outstanding properties, such as high charge carrier mobility,[3] long diffusion lengths,[4] ambipolar nature,[5,6] and solution processability, 3D perovskite semiconductors have raised renewed interest for adoption in field-effect transistors (FETs) after the pioneering work by Kagan et al.[7] in 1999 on two-dimensional perovskite FETs
While 3D perovskite FETs could be investigated as a possible new powerful candidate for lowcost, large-area, and flexible electronics, it is certainly a powerful platform to deepen the understanding of charge transport in semiconducting thin films.[8,9]
We have revealed the dynamic nature of the field effect in solution-processed 3D perovskite FETs, and we have proposed the adoption of transient measurements to study such an otherwise elusive phenomenon
Summary
Three-dimensional metal-halide perovskite semiconductors have shown tremendous performance in optoelectronic devices, with solar cells achieving laboratory power conversion efficiencies above 25%.1,2 Owing to their outstanding properties, such as high charge carrier mobility,[3] long diffusion lengths,[4] ambipolar nature,[5,6] and solution processability, 3D perovskite semiconductors have raised renewed interest for adoption in field-effect transistors (FETs) after the pioneering work by Kagan et al.[7] in 1999 on two-dimensional perovskite FETs. Halides and methylammonium defects are the most probable migrating ions as their activation energy is calculated to be as low as ∼0.1 eV for the iodide vacancies, 0.5 eV for MA+ vacancies, and 0.8 eV for Pb2+ vacancies.[29,34,35] Such species can either accumulate in response to the applied field, screening the gating, or form energetic barriers for intergrain transport of electronic charges when accumulating at grain boundaries.[21,36,37] When a short enough pulse is applied, the modulation of the electrical conductivity of the perovskite film is measurable since the time scale of the electronic channel accumulation is much faster than the ion migration one. On the basis of the data reported here, other effects interfering with the electronic field effect cannot be excluded, we note that the observation of FET operation for single-crystal perovskites at room temperature[23] is consistent with the proposed picture
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