Strong electron-ion coupling in gradient halide perovskite heterojunction
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RACT The electron-ion coupling in iontronics has great significance and potential for energy conversion and storage devices. However, it is a substantial challenge to integrate iontronics into all-solid-state semiconductor circuits and explore the electron-ion coupling in semiconductor devices. Here, by utilizing the organic-inorganic halide perovskite, we fabricate a planar heterojunction with a gradient distribution of halide anions. The diode-like halide migration was investigated by bias voltage induced asymmetric blue shift in photoluminescence spectrum. This pseudo-ionic diode behaviour was found to result from asymmetric charge injection characterized by I–V curves and gradient-halides-induced vacancy hopping indicated by energy dispersive spectroscopy (EDS). The planar gradient perovskite heterojunction provides a viable route for extending iontronic devices into the regime of all-solid-state semiconductors.
KEYWORDS halide perovskite films, gradient heterojunctions, electron-ion couplings, photoluminescence
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Introduction
Ionic migration, a fundamental and significant process in both biological and artificial systems, has intensive application such as sensors, energy conversion and flexible wearable devices [1–4]. It can be combined with the electronic signals for iontronics to enhance the functionality and performance of circuits and systems [5–11]. Considering the electrons manipulation of nowadays solid semiconductors, iontronic semiconductors in all solid state are in great demand for present integrated semiconductor circuits [12, 13]. They can combine the band gaps with ionic migration and increase carrier species in semiconductors from single electrons to the coupling of electrons and ions [14]. However, the majority of iontronic materials are organic polymers, electrolytes or hydrogels [15–19], because of their advantage of ionic exchange. It’s extremely difficult to realize all-solid-state iontronics due to the higher barrier of movable ions than electrons in the solid semiconductor. Recently, organic–inorganic halide perovskite appears as an advantageous semiconductor in both the optoelectronic research and industry [20–28]. One of the most attractive features of this perovskite is that the ions can migrate through unavoidable defects such as vacancies and grain boundaries; thus, this material is also known as an electron-ion semiconductor [29, 30]. Although the ionic migration causes hysteresis in solar cells [31–33] and phase segregation in luminescent devices [34–38], it opens a way to achieve controllable iontronics in semiconductor [39–41] and has some novel applications such as resistive switching of solid-state memory and light-induced energy storage devices [42, 43]. Furthermore, organic–inorganic halide perovskite Address correspondence to [email protected]
is somewhat compatible with both organic and inorganic devices for the junction [26], which benefits its integration within circuits. Here, the electron-ion coupling behaviour has been observed in a gradient halide perovskite hetero
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