The evolutionary success in information technology has been sustained by the rapid growth of sensor technology. Recently, advances in sensor technology have promoted the ambitious requirement to build intelligent systems that can be controlled by external stimuli along with independent operation, adaptivity, and low energy expenditure. Among various sensing techniques, field-effect transistors (FETs) with channels made of two-dimensional (2D) materials attract increasing attention for advantages such as label-free detection, fast response, easy operation, and capability of integration. With atomic thickness, 2D materials restrict the carrier flow within the material surface and expose it directly to the external environment, leading to efficient signal acquisition and conversion. This review summarizes the latest advances of 2D-materials-based FET (2D FET) sensors in a comprehensive manner that contains the material, operating principles, fabrication technologies, proof-of-concept applications, and prototypes. First, a brief description of the background and fundamentals is provided. The subsequent contents summarize physical, chemical, and biological 2D FET sensors and their applications. Then, we highlight the challenges of their commercialization and discuss corresponding solution techniques. The following section presents a systematic survey of recent progress in developing commercial prototypes. Lastly, we summarize the long-standing efforts and prospective future development of 2D FET-based sensing systems toward commercialization.

Two-Dimensional Field-Effect Transistor Sensors: The Road toward Commercialization.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/adfm.202101029

Switched-On: Progress, Challenges, and Opportunities in Metal Halide Perovskite Transistors

In the past few years, metal halide perovskites (MHPs) have received numerous attention for being applied in photovoltaics, light-emitting diodes and photodetectors due to their excellent optoelectronic characteristics. However, the utilization of MHPs for field-effect transistors (FETs) lags much behind, which is mainly attributed to the challenges in device fabrication and the less-than-expected performance of MHP-based FETs. Summarizing the recent developments in fabrication and performance of MHP-based FETs is essential to further optimize device fabrication processes and to enhance device performance. This review focuses on the recent advances and developments in the fabrication and performance of MHP-based FETs. To begin with, the basics of FETs are briefly introduced. Next, the advances of FETs using 3D and 2D MHPs as semiconductor layers are summarized and the strategies, which can be employed to enhance device performance, are discussed. Finally, brief conclusions and perspectives of MHP FETs are given. Overall, this review brings together important information that aids the fabrication of MHP-based FETs with reliable and enhanced performance, aiming to promote the advancement and application of MHP-based FETs.

Recent developments in fabrication and performance of metal halide perovskite field-effect transistors

Summary Single-crystal halide perovskites have demonstrated excellent optoelectronic properties and promising device application potentials, thanks to their remarkable carrier dynamics, solution processing procedures, and outstanding stabilities. The latest progress and future perspectives of single-crystal halide perovskites are reviewed herein. The basic properties and fundamental studies of single-crystal halide perovskites are first discussed. We then introduce the growth methods for these materials and summarize their recent developments. We further present the single-crystal halide perovskite devices among their major application fields. Finally, we discuss current challenges and provide some suggestions for their further development. We hope this paper can help readers understand the status and future challenges for single-crystal halide perovskites.

Single-crystal halide perovskites: Opportunities and challenges

Charge Transport in 2D Layered Mixed Sn–Pb Perovskite Thin Films for Field-Effect Transistors

2D Ruddlesden–Popper perovskites (2D PVKs) have attracted huge interest because of their excellent optoelectronic properties, yet the understanding of their electrical properties is inadequate due to the difficulties in obtaining 2D PVK field‐effect transistors (FETs) with decent performance. Herein, the fabrication and characterization of 2D PVK ((BA)2(MA)n−1PbnI3n+1) single crystal FETs are reported, which exhibit reliable field effect electrical characteristics at low temperatures. Kelvin probe force microscopy (KPFM) results reveal that both ion migration and contact resistance seriously degrade device performance. While ion migration can be suppressed at low temperatures, contact resistance seems to fundamentally determine device performance. On one hand, Schottky contacts are observed to form at the metal/2D PVK interface because of Fermi level pinning, resulting in significant charge injection resistance, although this can be remarkably improved by replacing Au electrodes with Ca. On the other hand, the out‐of‐plane mobility is found to be three orders of magnitude lower than the in‐plane mobility in 2D PVKs, causing large interlayer transport resistance. Thus, a low work‐function metal and a thin crystal are important for achieving high device performance. This work provides important experimental insights into fabrication and electrical properties of 2D PVK FETs.

2D Ruddlesden–Popper Perovskite Single Crystal Field-Effect Transistors

The porous organic polymer films (PFs) with intrinsical porosity and tuneable pore environment are ideally suited for application in electronic devices. However, the huge challenges still exist for construction of electronic devices based on PFs owing to lack of robustness, processability, and controllable preparation. Herein, we report the electrochemical preparation of carbazole-based porous organic polymer films (eCPFs) for memristors. These eCPFs possess the characteristics of controllable thickness/size, high stability, and excellent porosity. Carbazole and cyano groups are introduced into the eCPFs to constructing electron transfer systems, respectively. Thus the memristors constructed based on these eCPFs exhibit excellent switching performance, reliability, and reproducibility. The electrochemically controllable preparation method of porous organic polymer membranes proposed in this paper provides a feasible idea for the developments of electronic devices.

Electrochemical Preparation of Porous Organic Polymer Films for High-Performance Memristors.

In photodetectors based on heterojunctions of organic semiconductor and hybrid perovskite, the strong light absorbing ability of perovskite and the gate‐tunability of organic semiconductor can be preferably incorporated. However, the charge current transfer at the interface, and the double channel transportation in the heterojunctions are not fully understood. The authors successfully transfer the mechanically exfoliated Ruddlesden–Popper (RP) layered perovskite single crystal to the thermal evaporated organic small molecule semiconductor forming a heterojunction. Based on the heterojunction, two configurations of light detecting devices are prepared in which the perovskite layer acts as either a conducting channel and light absorbing layer or light absorbing layer only. The light detecting performance of such devices is systematically investigated. The charge transfer from the perovskite single crystal to the organic semiconductor layer is observed by Kelvin Probe Force Microscope characterization. They also find that the n values of the RP layered perovskite can significantly influence the property of the heterojunction and charge transfer process. For single channel devices a responsivity of 5.87 × 102 A W−1 and a detectivity of 5.13 × 1012 Jones is realized.

Phototransistors Based on Organic Small Molecules–Ruddlesden‐Popper Layered Perovskite Single Crystal Heterojunctions

Highly ordered semiconducting single-walled carbon nanotubes(sc-SWCNTs) array with high purity, high linear density and controllable manner is strongly desired for carbon-based integrated circuits, yet it remains a big challenge. Herein, close-packed single layered and controllably aligned sc-SWCNTs arrays were obtained through dielectrophoresis using a high purity sc-SWCNT dispersion. Under optimized condition of length and average number of interconnecting junctions across the channel full of aligned sc-SWCNTs, field effect transistors (FETs) with high performance were achieved with both a high on/off current ratio and large carrier mobility. Based on the optimized channel length, by systematically optimizing the dielectrophoresis parameters of the frequency and duration of applied AC voltage (V pp), the highly ordered sc-SWCNTs arrays with an ultra-high linear density of 54 ± 2 tubes μm−1 showed relatively high device performance of FET. The fabrication process optimized in this report can be further extended and applied in large-area, low-cost carbon-based integrated circuits.

Huijuan Sun

Papers

2D Ruddlesden–Popper Perovskite Single Crystal Field-Effect Transistors

Electrochemical Preparation of Porous Organic Polymer Films for High-Performance Memristors.

Phototransistors Based on Organic Small Molecules–Ruddlesden‐Popper Layered Perovskite Single Crystal Heterojunctions

Single layer aligned semiconducting single-walled carbon nanotube array with high linear density

Vacuum Pressure Leads to an Organic Molecular Electronic Response