3D/2D Hybrid Perovskite Heterostructures for Thin-Film Field-Effect Transistors

Organic-inorganic perovskites are hybrid materials with a three-dimensional (3D) structure which have recently been found to possess excellent optical and electronic properties, making them highly suitable for applications such as solar cells, light-emitting diodes, and thin film field-effect transistors (FETs)(1, 2). However, their poor stability under ambient conditions in the long term remains a challenge. Two-dimensional (2D) perovskites have emerged recently as excellent candidates to tackle this issue as they possess an organic spacer in their structure, which is hydrophobic in nature. In particular, the Ruddlesden-Popper (RP) phases of 2D perovskites have been reported to have good air-stability and higher resistance to degradation compared to 3D perovskites(3). In this work, we study 2D RP perovskites based on the spacer - isobutylammonium (iBA) and explore methods for integrating them into 3D perovskite thin film field-effect transistors fabricated using the state-of-the art triple-cation-composition(4). This spacer has only been sparingly studied in the literature so far in prototype optoelectronic devices.<br/>First, we investigate the optoelectronic and structural properties of 2D perovskite thin films of different <i>n</i> values, through characterization techniques such as photoluminescence imaging, x-ray diffraction measurements and scanning electron microscopy. We also examine their charge transport behavior and identify that they are insulating despite excellent film quality being achieved. Finally, we look into the incorporation of 2D perovskites into 3D perovskite thin films by forming 3D/2D perovskite heterostructures on the surface. We fabricated 3D/2D heterostructure perovskite FETs using solution processing via the anti-solvent method(5) and obtained the transfer characteristics. The control FET device which serves as the reference system in this study was thoroughly optimized in previous work(4) and it consists of a pure 3D perovskite of the state-of-the-art triple-cation-composition.<br/>Both the control and test devices exhibit transfer characteristics with distinctly n-type behavior and on/off ratios of ~10⁴ at room temperature. Surface passivation with iBA-based 2D perovskite resulted in a shift of the transfer curves with just a slightly lower current accompanied by a smaller turn-on voltage and sharper onset of the on-state. Remarkably, in the 3D/2D heterostructure FET, there is a reduction in the unwanted hysteresis which has been a persistent issue in these devices in the past. Our work presents an effective strategy to integrate 2D perovskites into 3D perovskite FETs, exploit the salient features of both components, and obtain improved device performance. Our research on 3D/2D heterostructure perovskite devices takes a step towards the realization of the predicted charge transport behavior of perovskite materials for various optoelectronic applications.<br/>References<br/>1. M. A. Green, A. Ho-Baillie, H. J. Snaith, The emergence of perovskite solar cells. Nature Photonics 2014, 8, 506-514.<br/>2. J. Wang et al., Investigation of electrode electrochemical reactions in CH₃NH₃PbBr₃perovskite single-crystal field-effect transistors. Advanced Materials 2019, 31, 1902618.<br/>3. Y. Chen et al., 2D Ruddlesden-Popper perovskites for optoelectronics. Advanced Materials 2018, 30, 1703487.<br/>4. S. P. Senanayak et al., A general approach for hysteresis-free, operationally stable metal halide perovskite field-effect transistors. Science Advances 2020, 6, eaaz4948.<br/>5. M. Saliba et al., Cesium-containing triple cation perovskite solar cells: Improved stability, reproducibility and high efficiency. Energy & Environmental Science 2016, 9, 1989-1997.