Two-Dimensional Lead-Free Perovskite (C6H5C2H4NH3)2CsSn2I7 with High Hole Mobility

[NH3(CH2)4NH3]SnX4 (X = Br, I): Dion-Jacobson type 2-D perovskites with short interlayer spacing

Two-dimensional tin(II) halide perovskites stand as an environmentally benign alternative to Pb(II) halide perovskites. However, they are often challenging to make due to the oxidation of Sn(II) ion to more stable Sn(IV) ion. Here we report hybrid tin bromide and iodide perovskites: (1,4-BDA)Sn(IV)Br6 and (1,4-BDA)Sn(II)X4 (where X = Br, I; 1,4-BDA = 1,4-diammoniumbutane) with 0D and 2D structures, respectively. Their synthesis, structural characterization and photophysical properties are reported. They show bandgaps in the 1.94-2.70 eV range.

Unlocking the Potential of Tin-Based Perovskites: Properties, Progress, and Applications in New-Era Electronics

Electronics have greatly promoted the development of modern society and the exploration of new semiconducting materials with low cost and high mobility continues to attract interest in the advance of next-generation electronic devices. Among emerging semiconductors, the metal-halide perovskite, especially the nontoxic tin (Sn)-based candidates, has recently made breakthroughs in the field of diverse electronic devices due to its excellent charge transport properties and cost-effective large-area deposition capability at low temperatures. To enable a more comprehensive understanding of this emerging research field and promote the development of new-generation perovskite electronics, this review aims to provide an in-depth understanding with the discussion of unique physical properties of Sn-based perovskites and the summarization of recent research progress of Sn-based perovskite field-effect transistors (FETs) and diverse electronic devices. The unique character of negligible ion migration is also discussed, which is fundamentally different from the lead-based counterparts and provides a great prerequisite for device application. The following section highlights the potential broad applications of Sn-perovskite FETs as a competitive and feasible technology. Finally, an outlook and remaining challenges are given to advance the progression of Sn-based perovskite FETs, especially on the origin and solution of stability problems toward high-performance Sn-based perovskite electronics.

Sn-Based Perovskite Halides for Electronic Devices

Because of its less toxicity and electronic structure analogous to that of lead, tin halide perovskite (THP) is currently one of the most favorable candidates as an active layer for optoelectronic and electric devices such as solar cells, photodiodes, and field-effect transistors (FETs). Promising photovoltaics and FETs performances have been recently demonstrated because of their desirable electrical and optical properties. Nevertheless, THP's easy oxidation from Sn2+ to Sn4+ , easy formation of tin vacancy, uncontrollable film morphology and crystallinity, and interface instability severely impede its widespread application. This review paper aims to provide a basic understanding of THP as a semiconductor by highlighting the physical structure, energy band structure, electrical properties, and doping mechanisms. Additionally, the key chemical instability issues of THPs are discussed, which are identified as the potential bottleneck for further device development. Based on the understanding of the THPs properties, the key recent progress of THP-based solar cells and FETs is briefly discussed. To conclude, current challenges and perspective opportunities are highlighted.

Review on Perovskite Semiconductor Field-Effect Transistors and Their Applications

Perovskite materials are considered as the most alluring successor to the conventional semiconductor materials to fabricate solar cells, light emitting diodes and electronic displays. However, the use of the perovskite semiconductors as a channel material in field effect transistors (FET) are much lower than expected due to the poor performance of the devices. Despite low attention, the perovskite FETs are used in widespread applications on account of their unique opto-electrical properties. This review focuses on the previous works on perovskite FETs which are summarized into tables based on their structures and electrical properties. Further, this review focuses on the applications of perovskite FETs in photodetectors, phototransistors, light emitting FETs and memory devices. Moreover, this review highlights the challenges faced by the perovskite FETs to meet the current standards along with the future directions of these FETs. Overall, the review summarizes all the available information on existing perovskite FET works and their applications reported so far.

Formamidinium Perovskitizers and Aromatic Spacers Synergistically Building Bilayer Dion-Jacobson Perovskite Photoelectric Bulk Crystals

Two-dimensional (2D) multilayer Dion-Jacobson (DJ) phase organic inorganic hybrid perovskites (OIHPs) have attracted extensive research attention due to the high stability and excellent charge-transport properties in the optoelectronic field. However, the synthesis of 2D multilayer DJ OIHPs is still very challenging. Until now, only few multilayer DJ perovskites have been reported and most of them are based on volatile methylamine (MA) cations. Compared with MA-based OIHPs, the OIHPs constructed with formamidinium (FA) as perovskitizers not only improve the stability but also extend the light absorption range. Meanwhile, the introducing aromatic diamines as spacers could promote the electron-hole separation in such DJ hybrids. However, the DJ OIHP bulk single crystal constructed by using the advantages of FA as perovskitizers and aromatic diamines as spacers is still blank. Herein, we integrate the properties of organic cations and inorganic skeletons at a molecular-scale to construct a broadband-responsive 2D bilayer DJ perovskite (3AMPY)(FA)Pb₂I₇ [3AMPY = 3-(aminomethyl)pyridinium], which shows a fascinating detectivity from X-ray (5.23 × 10⁴ μC Gy_air^-1 cm^-2 at 200 V bias) and visible light (6 × 10¹² jones at 637 nm) to the near-infrared region (2.6 × 10⁹ jones at 780 nm). After an in-depth analysis of structure and optical properties, we found that the distortion degree of Pb-I-Pb bond angles between adjacent PbI₆ octahedra plays a crucial role on optical properties; on the other hand, the interlayer spacer cations (3AMPY) and intralayer perovskitizers (FA) mutual participate in the contribution of the conduction band, making (3AMPY)(FA)Pb₂I₇ have a narrow optical band gap of 1.54 eV. Such a 2D perovskite material with a wide spectra response will be the preferred choice for photodetection under complex conditions.

Dimensional structure regulation of organic-inorganic hybrid perovskite and its application in thin film transistors

The effects of dimensional structure on the properties of lead iodide perovskite (C₈H₉NH₃)₂(CH₃NH₃)_n-1Pb_nI_3n+1were investigated. Furthermore, perovskite thin films with different dimensionalities were applied as the channel layer of thin film transistors (TFT). The electrical performance and stability of TFT devices were significantly improved through the regulation of dimensional microstructure of the perovskites. As a result, the quasi-2D (n = 6) perovskite TFTs achieved a field-effect mobility (μ_FE) of 3.90 cm²V^-1s^-1, with 10⁴on-off current ratio and -1.85 V threshold voltage, which can be maintained well after 4 days without degradation at 30% ambient humidity. Moreover, the electrical performance of the TFTs based on Pure-2D and Quasi-2D perovskite also exhibited a good bias stability.

Structure-Electronic Property Relationships of 2D Ruddlesden-Popper Tin- and Lead-based Iodide Perovskites

Two-dimensional (2D) halide perovskites are receiving considerable attention for applications in photovoltaics, largely due to their versatile composition and superior environmental stability over three-dimensional (3D) perovskites, but show much lower power conversion efficiencies. Hence, further understanding of the structure-property relationships of these 2D materials is crucial for improving their photovoltaic performance. Here, we investigate by means of first-principles calculations the structural and electronic properties of 2D lead and tin Ruddlesden-Popper perovskites with general formula (BA)₂A_n-1B_nI_3n+1, where BA is the butylammonium organic spacer, A is either methylammonium (MA) or formamidinium (FA) cations, B represents Sn or Pb atoms, and n is the number of layers (n = 1, 2, 3, and 4). We show that the band gap progressively increases as the number of layers decreases in both Sn- and Pb-based materials. Through substituting MA by FA cations, the band gap slightly opens in the Sn systems and narrows in the Pb systems. The electron and hole carriers show small effective masses, which are lower than those of the corresponding 3D perovskites, suggesting high carrier mobilities. The structural distortion associated with the orientation of the MA or FA cations in the inorganic layers is found to be the driving force for the induced Rashba spin-splitting bands in the systems with more than one layer. From band alignment diagrams, the transfer process of the charge carriers in the 2D perovskites is found to be from smaller to higher number of layers n for electrons and oppositely for holes, in excellent agreement with experimental studies. We also find that, when interfaced with 3D analogues, the 2D perovskites could function as hole transport materials.

Aqueous Synthesis of Low-Dimensional Lead Halide Perovskites for Room-Temperature Circularly Polarized Light Emission and Detection

Low-dimensional lead halide perovskite materials are an emerging class of solution-processable semiconductors with promising potential applications in optoelectronic devices. Unfortunately, it is impossible to synthesize high-crystalline-quality low-dimensional perovskite single crystals without using chemotoxic solutions such as dimethylformamide/dimethyl sulfoxide or applying heating. Herein we report an economical and universal aqueous method to synthesize 2D layered and 1D chain perovskite single crystals at room temperature. The resultant chiral 2D perovskites can efficiently and selectively emit and detect circularly polarized light at room temperature. The as-synthesized 1D perovskite single crystals exhibit strong quantum confinement and enhanced self-trapped states that give efficient warm circularly polarized white-light emission. This aqueous synthetic method is general for other high-quality low-dimensional lead halide perovskite single crystals, and thus our findings would motivate more fundamental investigations on low-dimensional perovskites for potential optoelectronic applications.

Interfacial Engineering Determines Band Alignment and Steers Charge Separation and Recombination at an Inorganic Perovskite Quantum Dot/WS2 Junction: A Time Domain Ab Initio Study

Using time-domain density functional theory and nonadiabatic (NA) molecular dynamics, we demonstrate that interfacial interaction between WS₂ and CsPbBr₃ quantum dots (QDs) determines the band alignment, leading to a type-II and type-I heterojunction for the WS₂ contacting with Cs/Br- and PbBr₂-terminated facet QD, respectively. In the type-II heterojunction, electron transfer is faster than hole transfer arising due to the stronger NA coupling, higher density of electron acceptor states, and more and higher phonon modes involved. Both the electron and hole transfer times are subpicosecond, in agreement with experiments. The energy lost by the electron and hole is slower than charge transfer by several times, facilitating keeping charge carriers sufficiently "hot". Particularly, the electron-hole recombination occurs over 1 ns, favoring a long-lived charge-separated state. Detailed atomistic insights into the photoinduced charge and energy dynamics at the WS₂/QD interface provide valuable guidelines for improving performance of perovskite/transition-metal dichalcogenide solar cells.