Transistors

Researchers from POSTECH, SKKU and UESTC have developed air‑stable tin‑based perovskite p‑type transistors using volatile surface reconstruction by treating CsSnI₃ with potassium acetate, removing defect‑forming tin ions and creating a protective KI layer. The devices show top‑level hole mobility and on/off ratio, remain stable in air and at high temperature, and may be used in future memory and display electronics.

Tin (Sn²⁺) halide perovskites are promising lead‑free materials for future electronics because their bandgaps can be tuned and they conduct charge efficiently, but the tin at the surface is easily oxidized in air. Undercoordinated Sn²⁺ sites tend to oxidize to Sn⁴⁺, causing unwanted self‑doping and defects that block charge flow, so conventional tin‑based perovskite transistors can fail within minutes under ambient conditions. In these devices, unreacted tin ions that never fully joined the crystal remain on the surface and act as starting points for oxidation and degradation. To overcome this, the researchers implemented “volatile surface reconstruction”. 

Researchers from the Max Planck Institute for Polymer Research, Hong Kong Polytechnic University, University of Toronto and Norwegian University of Science and Technology (NTNU) have developed a new processing strategy that enables the formation of highly ordered Dion-Jacobson (DJ) phase tin-based perovskite thin films, addressing a key bottleneck in their application in field-effect transistors (FETs).

Schematic illustration of the SVAD process for deposition of DJ-type 2D layered Sn-based perovskite thin films. Image from: JACS

DJ perovskites are an emerging class of semiconductors composed of inorganic [SnI₆]⁴⁻ octahedral layers separated by organic diammonium cations. While their structure offers enhanced stability compared to other layered perovskites, their practical implementation has been limited by poor control over nucleation and crystallization during solution processing. In particular, the requirement that diammonium cations simultaneously connect adjacent inorganic layers makes the self-assembly of well-ordered films significantly more difficult. To overcome this challenge, the researchers introduced a solvent vapor assisted drop casting (SVAD) method. 

Researchers from Hanyang University, Samsung Electronics and Pohang Accelerator Laboratory have reported a breakthrough in the development of thin-film transistors using tin halide perovskites as p-type channel materials. Their work addresses longstanding challenges related to the instability and high defect density of three-dimensional tin halide perovskites, which have until now limited their practical application.

The team focused on formamidinium tin iodide (FASnI₃), a promising candidate for high-performance transistor channels, and introduced a new strategy involving methylammonium chloride (MACl). Unlike its behavior in lead halide perovskites - where MACl acts only as a temporary stabilizer - here, MACl is actually incorporated into the perovskite crystal structure, replacing part of the formamidinium (FA) and iodide (I) content with methylammonium (MA) and chloride (Cl). This compositional adjustment leads to a more stable crystal lattice, resulting in thin films with superior quality, improved crystallinity, and larger grain sizes.

Researchers from Xi’an Jiaotong University, Xi’an University of Architecture and Technology and Shanxi University have developed an integrated hole transport layer (HTL) strategy that enhances the efficiency, stability, and scalability of large-area perovskite solar cells (PSCs).

Uniform and durable HTLs are critical for achieving high-performance PSCs suitable for industrial-scale manufacturing. However, conventional self-assembled monolayer (SAM)-based HTLs often face challenges such as weak interfacial adhesion, poor film uniformity, and limited operational stability. To overcome these challenges, the research team proposed an in situ SAM anchoring approach carried out during NiOx nanoparticle synthesis, forming a robust chemically bonded [2PACz–NiOx] interface.

3D perovskite solar cells (PSCs) have reached impressive power conversion efficiencies, but their poor resistance to heat, moisture, and light continues to hinder commercialization. Quasi-2D perovskites offer a pathway toward greater stability, yet their performance is often compromised by insulating organic cations and disordered phase distribution.

In a recent study, researchers from China's Jinan University introduced a new multifunctional additive - formamidinium 4-methylbenzenesulfonate (FATsO) - to overcome these challenges. FATsO simultaneously passivates iodide anions and lead ion defects while strengthening the [PbI₆]₄⁻ framework through hydrogen bonding and Lewis acid–base interactions. The –NH²⁺ group stabilizes the crystal lattice, while the –SO₃⁻ group reduces uncoordinated Pb2+ defects. At the same time, hydrogen bonding between PEA⁺ and the –SO₃⁻ group restricts PEA⁺ diffusion, ensuring a more uniform phase distribution and facilitating efficient energy transfer.

One of the persistent challenges holding back perovskite solar cells lies in the way their hole transport layers (HTLs) are prepared. Traditionally, organic semiconductors like Spiro-OMeTAD or PTAA are “doped” using additives such as lithium bis(trifluoromethane)sulfonimide (LiTFSI). While the process works, it’s far from ideal: it depends on a slow and unpredictable oxidation reaction in air, while the leftover lithium ions become a hidden culprit of long‑term instability, drifting inside the device and eventually degrading performance.

To overcome these drawbacks, researchers from North China Electric Power University and Beijing Huairou Laboratory developed a new strategy they called electrolysis doping. Instead of relying on ambient chemistry, they directly apply an electrical bias that allows the semiconductor to be oxidized in a clean, controlled way on the anode surface. At the same time, the excess lithium ions are reduced at the cathode and effectively removed. The result is a dual benefit — a precisely doped organic semiconductor and the elimination of the mobile ions that undermine stability.

Researchers from National Taiwan University, National Synchrotron Radiation Research Center and Academia Sinica have developed a strategy for enhancing the performance and stability of tin-based perovskite transistors by incorporating porphyrin-like additives. 

The research team focused on two additives: H₂Pc and SnPc, both of the phthalocyanine family and known for their strong chemical stability and ability to interact with metal ions. When added to perovskite precursor solution, they help suppress the oxidation of tin ions and improve overall film quality. As a result, the transistors exhibited significantly higher charge mobility (up to 4.40 cm² V⁻¹ s⁻¹) and improved resistance to environmental degradation. The additives also increased grain sizes and reduced defects, which are critical for efficient charge transport.

Researchers from Shandong University of Science and Technology, Ocean University of China, Qingdao University and Southeast University have developed a method to block lead leakage and heal defects across all interfaces  in perovskite solar cells.

The team utilized a designed MOF: Co-bpdc (where bpdc=4,4’-biphenyldicarboxylate), to modify the top surface of the perovskite. The unique structure and abundant oxygen sites of Co-bpdc enable it to react completely with Pb²⁺, thereby hindering the escape of Pb²⁺ ions. Additionally, they employed polyethyleneimine (PEI), a material commonly used in industrial wastewater treatment, at the buried interface of the perovskite. PEI possesses dense amino groups, enabling it to act as heterogeneous nucleation sites to facilitate the growth of larger grains and enhance film quality. 

A research team, led by Professor Yong-Young Noh and Dr. Youjin Reo from the Department of Chemical Engineering at POSTECH (Pohang University of Science and Technology), has developed p-channel Sn²⁺-halide perovskite TFTs using a thermal evaporation approach with inorganic caesium tin iodide (CsSnI₃). 

The project was a collaborative effort with Professors Ao Liu and Huihui Zhu from the University of Electronic Science and Technology of China (UESTC) and resulted in the development of high-performance, stable p-channel CsSnI₃-based TFTs using a commercially compatible vapor-deposition approach with PbCl₂ as an additive. The volatile chloride triggers solid-state reactions and the conversion of as-evaporated precursor compounds. This facilitates the formation of high-quality and uniform perovskite films, and also modulates the high hole density, making them suitable for use as channel layers. The optimized CsSnI₃:PbCl₂ TFTs delivered average µFE of around 34 cm2 V⁻¹ s⁻¹, on/off ratio of around 10⁸ and storage stability of more than 150 days. The team also demonstrated a large-scale Sn²⁺-halide perovskite TFT array that overcomes the technical challenges faced in the solution process. The vapor-deposited TFTs could be used in backplanes for organic light-emitting diode displays, or in logic devices and circuits for monolithic three-dimensional integration, where low process temperatures are required.

Solution-processed tin (Sn²⁺)-halide perovskites can be used to create p-channel thin-film transistors (TFTs) with performance levels comparable with commercial low-temperature polysilicon technology. However, high-quality perovskite film deposition using industry-compatible production techniques remains challenging. 

To address this challenge, researchers at Pohang University of Science and Technology, Korea Research Institute of Standards and Science and University of Electronic Science and Technology of China have fabricated p-channel Sn²⁺-halide perovskite TFTs using a thermal evaporation approach with inorganic caesium tin iodide (CsSnI₃).