Transistors

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). 

Researchers from China's Hebei University of Technology, Fudan University, Fuyang Normal University, Chinese Academy of Sciences (CAS), Macau University of Science and Technology, Kunming University of Science and Technology and France's CNRS have reported an innovative passivation strategy that is said to enable record power conversion rates and enhanced operational longevity of single junction and tandem perovskite solar cells (PSCs).

The team has developed this innovative strategy to address the issue of interfacial trap-assisted nonradiative recombination, which has been known to hinder the performance of perovskite-based photovoltaic technologies. The new passivator is identified as L-valine benzyl ester p-toluenesulfonate (VBETS) and using it under optimal conditions yielded PSCs that achieved a power conversion efficiency (PCE) of 26.28%. 

Researchers from Northwestern University, Arizona State University, University of Toronto and National University of Singapore have addressed the issue of ion migration, which deteriorates the performance and stability of perovskite solar cells (PSCs). The team has developed a new method to improve the stability and efficiency of PSCs through surface functionalization, which uses a chemical compound called 5-ammonium valeric acid iodide (5-AVAI) to enable the uniform growth of aluminum oxide (Al₂O₃) through atomic layer deposition. This process creates a robust barrier that suppresses halide migration by more than an order of magnitude.

Using this method, the researchers tested solar cells, and found that they retained 90% of their initial power conversion efficiency (PCE) after 1,000 hours of continuous operation at 55 degrees Celsius under full sunlight, compared to less than 200 hours without the barrier layer. 

Researchers from Pakistan's University of Engineering & Technology (UET) and National University of Technology have reported the use of manual screen printing to fabricate semi-transparent, scalable perovskite solar modules without the requirement for numerous laser-scribing steps. 

A carbon-based, hole-transport-layer-free perovskite solar module with a power conversion efficiency of 11.83% was manufactured, with an active area of 900 cm². Accelerated testing was done in settings with elevated humidity, high sun irradiation, and harsh temperatures to determine whether these modules are ready for the market. 

Researchers from India's Madan Mohan Malaviya University of Technology, University of Delhi, Manipal University and Sweden's IAAM have combined 2D and 3D perovskites to strengthen both reliability and efficiency of 3D perovskite solar cells (PSCs). 

The team explored the combined effect of Dion-Jacobson (DJ) 2D-3D halide-based perovskites layers on device performance. The DJ 2D material used was PeDAMA₄Pb₅I₁₆, while the 3D material is the lead-free, stable CsGeI_3-xBr_x (with x=1). The optimized solar cell structure developed in this work consisted of (Au/Cu₂O/PeDAMA₄Pb₅I₁₆/CsGeI_3-xBr_x/PCBM/FTO). 

Perovskite solar cells (PSCs) that incorporate a 2D/3D perovskite layer tend to demonstrate enhanced stability compared to that of their purely 3D counterparts, possibly thanks to the superior chemical stability of the 2D perovskite layer. However, the poor electrical properties of the 2D perovskite layer also limit further improvement of device performance. Moreover, the most effective hole transport layer (HTL) in 2D/3D PSCs, lithium bis(trifluoromethylsulfonyl)imide (Li-TFSI)-doped 2,2′,7,7′-tetrakis(N,N-di(4-methoxyphenyl)amino)-9,9-spirobifluorene (spiro-OMeTAD), usually needs prolonged exposure to air to improve its conductivity, which to some extent increases the risk of water/oxygen infiltrating into the perovskite layer, leading to the degradation of the perovskite active layer.

Researchers at China's Henan University and Chinese Academy of Sciences (CAS) have developed a multifunctional dopant, tin oxysulfide (SnSO) in the spiro-OMeTAD layer, to improve the efficiency and stability simultaneously.

Tokyo Chemical Industry (TCI), a global supplier of laboratory chemicals and specialty materials, is now offering Phenylethylamine Hydroiodides materials, used for surface treatment of perovskite layers in solar panels. These materials improve the stability of the solar panels.

Research has shown that by applying the Phenylethylamine Hydroiodides materials, one can expect improved stability of over 90%. In one research, the 1,2-Benzenediethanamine Dihydroiodide was applied to a perovskite PV device (FTO/TiO2/SnO2/perovskite/Amine Iodide/Spiro-OMeTAD/Au), and achieved an increase in stability of over 90% after 1,100 hours. See here for more info.

Researchers from China's National Center for Nanoscience and Technology, Chinese Academy of Sciences (CAS) and Beihang University have demonstrated a series of ultrastable Dion−Jacobson (DJ) perovskites for photovoltaic applications. They went on to develop a 2D Dion-Jacobson (DJ) perovskite solar cell that showed high stability while achieving a power conversion efficiency of 19.11%.

Schematic illustration of the blade-coating film and the corresponding device configuration under atmospheric environment at room temperature. Image credit: Nature Communications 

Two-dimensional (2D) Dion-Jacobson (DJ) phase perovskites have drawn attention from academia due to their stability against harsh environmental conditions and their competitive performance in optoelectronic applications. Solar cells based on DJ perovskites, however, have so far shown comparatively poor performance compared to their 3D counterparts.

The majority of monolithic perovskite/Si tandem solar cells (TSCs) have been built on heterojunction (HJT) Si solar cells, which have seen limited industrial uptake due to manufacturing cost and concern over the viability of metal electrodes and transparent conductive oxides (TCOs) incorporating expensive elements. Recently, researchers from The Australian National University, University of Melbourne and University of New South Wales demonstrated that high efficiencies of perovskite/Si TSCs can be achieved with Si bottom cells based on a double-side poly-Si/Si dioxide (SiO₂) passivating contact (poly-Si cell) without silver or transparent conductive oxides (TCOs), fabricated using mass-production techniques. 

In addition, a novel low-absorption, dopant-free bilayer-structured hole transport layer (HTL) composed of ultra-thin poly(N,N′-bis-4-butylphenyl-N,N′-bisphenyl)benzidine (Poly-TPD) and 2,2′,7,7′-tetra(N,N-di-p-tolyl)amino-9,9-spirobifluorene (Spiro-TTB) double layers was developed for the perovskite top cell, which passivates the perovskite surface and enhances the near-interface conductivity, thus increasing the open-circuit voltage and fill factor.