Investigation of Electrode Electrochemical Reactions in CH3 NH3 PbBr3 Perovskite Single-Crystal Field-Effect Transistors.

Optoelectronic devices based on metal halide perovskites, including solar cells and light-emitting diodes, have attracted tremendous research attention globally in the last decade. Due to their potential to achieve high carrier mobilities, organic-inorganic hybrid perovskite materials can enable high-performance, solution-processed field-effect transistors (FETs) for next-generation, low-cost, flexible electronic circuits and displays. However, the performance of perovskite FETs is hampered predominantly by device instabilities, whose origin remains poorly understood. Here, perovskite single-crystal FETs based on methylammonium lead bromide are studied and device instabilities due to electrochemical reactions at the interface between the perovskite and gold source-drain top contacts are investigated. Despite forming the contacts by a gentle, soft lamination method, evidence is found that even at such "ideal" interfaces, a defective, intermixed layer is formed at the interface upon biasing of the device. Using a bottom-contact, bottom-gate architecture, it is shown that it is possible to minimize such a reaction through a chemical modification of the electrodes, and this enables fabrication of perovskite single-crystal FETs with high mobility of up to ≈15 cm2 V-1 s-1 at 80 K. This work addresses one of the key challenges toward the realization of high-performance solution-processed perovskite FETs

A general approach for hysteresis-free, operationally stable metal halide perovskite field-effect transistors.

Despite sustained research, application of lead halide perovskites in field-effect transistors (FETs) has substantial concerns in terms of operational instabilities and hysteresis effects which are linked to its ionic nature. Here, we investigate the mechanism behind these instabilities and demonstrate an effective route to suppress them to realize high-performance perovskite FETs with low hysteresis, high threshold voltage stability (ΔVt 1 cm2/V·s at room temperature. We show that multiple cation incorporation using strain-relieving cations like Cs and cations such as Rb, which act as passivation/crystallization modifying agents, is an effective strategy for reducing vacancy concentration and ion migration in perovskite FETs. Furthermore, we demonstrate that treatment of perovskite films with positive azeotrope solvents that act as Lewis bases (acids) enables a further reduction in defect density and substantial improvement in performance and stability of n-type (p-type) perovskite devices

Device Physics of Organic-Inorganic Hybrid Perovskite Semiconductors

This dissertation explores various aspects of metal halide perovskite semiconductors for photovoltaic and optoelectronic applications. The research focuses on addressing key challenges and advancing the understanding of perovskite field-effect transistors (FETs) for improved device performance. The study begins by investigating electrochemical reactions occurring at the interface between the perovskite and gold metal electrode in perovskite single crystal FETs. By delaminating the electrodes and employing surface analytical techniques, it is revealed that an electrochemical reaction occurs during device operation. This issue is mitigated by modifying the electrode with organic interlayers, leading to the demonstration of single crystal perovskite transistors with the highest reported mobilities of up to 15cm²/Vs at low temperatures. Subsequently, the research tackles challenges related to low mobility, high trap density, and hysteresis in low-dimensional perovskite FETs. Comparative studies involving different dielectric layers and a low-temperature bromide chemistry route are conducted to reduce charged impurities and trap densities, resulting in improved device performance. High mobilities of up to 10cm²/V s at room temperature are achieved in PEASnI₄ transistors through interface engineering. Finally, the dissertation explores the doping of metal halide perovskites as a means to control charge carrier concentration. An additive-assisted strategy is developed for n-type molecular doping of organic-inorganic hybrid perovskite (OIHP) MAPbI₃, with a specific focus on the effects of electron donor CsF. Doping at the top of the perovskite film leads to enhanced FET performance, with reliable electron mobility significantly improved up to 5cm²/V s. This approach offers a promising method for effectively doping perovskite MAPbI₃ and holds implications for other optoelectronic applications, including solar cells and LEDs. In summary, this dissertation contributes to the advancement of perovskite-based optoelectronic devices, providing valuable insights into interface engineering, materials doping, and device optimization. The findings pave the way for the development of high-performance perovskite FETs and offer promising avenues for future research and practical applications in the field of perovskite-based optoelectronics

Anisotropic Piezoelectric Properties of Porous (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ Ceramics with Oriented Pores through TBA-Based Freeze-Casting Method

Porous (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 (BCZT) piezoelectric ceramics with an oriented directional hole structure were prepared by using the tertbutyl alcohol (TBA)-based freeze-casting method. The influences of sintering temperatures on the microstructure and piezoelectric properties of porous BCZT ceramics were investigated both perpendicular and parallel to the freezing direction. With the increase in sintering temperatures and the porosities decreased from 58% to 42%, the compressive strength increased from 14.0 MPa to 25.0 MPa. In addition, the d33 value of 407 pC/N for the sample sintered at 1400 °C was obtained parallel to the freezing direction, which was 1.40 times that of the other direction

A general approach for hysteresis-free, operationally stable metal halide perovskite field-effect transistors.

Despite sustained research, application of lead halide perovskites in field-effect transistors (FETs) has substantial concerns in terms of operational instabilities and hysteresis effects which are linked to its ionic nature. Here, we investigate the mechanism behind these instabilities and demonstrate an effective route to suppress them to realize high-performance perovskite FETs with low hysteresis, high threshold voltage stability (ΔVt 1 cm2/V·s at room temperature. We show that multiple cation incorporation using strain-relieving cations like Cs and cations such as Rb, which act as passivation/crystallization modifying agents, is an effective strategy for reducing vacancy concentration and ion migration in perovskite FETs. Furthermore, we demonstrate that treatment of perovskite films with positive azeotrope solvents that act as Lewis bases (acids) enables a further reduction in defect density and substantial improvement in performance and stability of n-type (p-type) perovskite devices

A general approach for hysteresis-free, operationally stable metal halide perovskite field-effect transistors.

Despite sustained research, application of lead halide perovskites in field-effect transistors (FETs) has substantial concerns in terms of operational instabilities and hysteresis effects which are linked to its ionic nature. Here, we investigate the mechanism behind these instabilities and demonstrate an effective route to suppress them to realize high-performance perovskite FETs with low hysteresis, high threshold voltage stability (ΔVt 1 cm2/V·s at room temperature. We show that multiple cation incorporation using strain-relieving cations like Cs and cations such as Rb, which act as passivation/crystallization modifying agents, is an effective strategy for reducing vacancy concentration and ion migration in perovskite FETs. Furthermore, we demonstrate that treatment of perovskite films with positive azeotrope solvents that act as Lewis bases (acids) enables a further reduction in defect density and substantial improvement in performance and stability of n-type (p-type) perovskite devices

Spin‐coating fabrication of high‐yield and uniform organic thin‐film transistors via a primer template growth

Publication status: PublishedAbstractSolution coating of organic semiconductors offers great potential for achieving low‐cost and high‐throughput manufacturing of large‐area and flexible electronics. However, the solution processability of semiconducting small molecules for fabricating uniform and reliable thin‐film devices poses challenges due to the low viscosities of small‐molecule solutions. Here, we report a universal approach employing a primer template (PT) to enhance the spreadability of small‐molecule solutions on silicon wafers, enabling the spin‐coating fabrication of uniform thin films composed of millimeter‐scale grains with complete large‐area coverage and well‐ordered molecular packing. Using PT, we fabricated organic thin‐film transistors (OTFTs) using solutions containing various small molecules such as rubrene and 2‐decyl‐7‐phenyl‐[1]benzothieno[3,2‐b][1]benzothiophene. The device yield of all fabricated OTFTs is consistently 100% while achieving a high average mobility of 1.62 cm2 V−1 s−1 with a device‐to‐device variation of 7.7% measured in ambient air condition. In addition, the utilization of PT resulted in a batch‐to‐batch variation of 12.5% in device performance over dozens of OTFT devices. The key industrial manufacturing metrics, such as device yield, reproducibility, and performance uniformity of the PT OTFTs, are among the best for devices fabricated using solution spin‐coating techniques.</jats:p