Technical / research

Researchers from the University of Science and Technology of China (USTC) of the Chinese Academy of Sciences have addressed a critical challenge in perovskite light-emitting diodes (PeLEDs) by identifying and targeting the root cause of efficiency loss at high brightness, and enabled record-breaking device performance by introducing a novel material design.

Using a self-developed diagnostic tool called electrically excited transient absorption (EETA) spectroscopy, the researchers captured real-time carrier dynamics in operating devices. They found that the hole leakage into the electron transport layer-previously undetected due to a lack of in situ characterization methods-is the primary culprit behind efficiency roll-off.

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.

Researchers at the Hong Kong Polytechnic University (PolyU) and Hong Kong University of Science and Technology (HKUST) have developed an innovative laminated interface microstructure that enhances the stability and photoelectric conversion efficiency of inverted perovskite solar cells.

Prof. ZHOU Yuanyuan, Associate Professor in the Department of Chemical and Biological Engineering (CBE) and Associate Director of the Energy Institute at HKUST, leads a team focused on fundamental research into perovskite optoelectronic devices from a unique structural perspective. They collaborated closely with Prof. CAI Songhua’s team from the Department of Applied Physics at PolyU. Their research revealed that by uniformly creating a “molecular passivation layer-fullerene derivative layer-2D perovskite layer”—a “three-ply” laminated structure on the surface of the perovskite film—they could effectively reduce the density of interface defects and improve energy level alignment. This advancement substantially boosts the photoelectric conversion efficiency of the perovskite solar cell and enhances the durability of the interface under damp-heat and light soaking conditions.

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 at Japan's National Institute of Advanced Industrial Science and Technology (AIST) and the UK's University of Oxford have asserted that while perovskite-on-silicon tandem solar cells are highly promising, the intrinsic multilayer device design presents challenges in complexity, which can be a drawback in future mass production. To this end, they developed a TiO_x layer (∼3–5 nm) grown by atomic layer deposition (ALD), that enables a series interconnection of a perovskite n-i-p top cell with a silicon wafer directly. 

A photo of the tandem solar cell fabricated on a 25 mm × 25 mm Si substrate. Image from: Small

The TiO_x layer serves as an all-in-one interconnect, fulfilling the functions of silicon surface passivation, hole extraction from silicon, and recombination junction at the top/bottom cell interface. As a result, a proof-of-concept 22.4%-efficient tandem device was demonstrated. Furthermore, an improved PCE of 26.5% was achieved by capping the TiOx with a thin ALD-TiNy layer (∼4 nm). 

Ultraviolet (UV)-induced damage and limited solar spectrum utilization can hinder the performance of perovskite solar cells (PSCs). In a recent study, researchers from Fuzhou University and Chinese Academy of Sciences developed a thermally activated delayed fluorescent (TADF) molecule, 4CzIPN, to address these challenges. 

Acting as a down-conversion agent, 4CzIPN can convert UV light to visible light via Förster energy transfer, enhancing light absorption and reducing photon loss. Additionally, it can bind Pb²⁺ defects and prevents organic cation degradation through cationic π-effects, stabilizing the perovskite structure. By serving as a crystal growth site, 4CzIPN can promote intermediate phase formation and delay the crystallization process, and improve film quality while mitigating residual stress due to its high thermal expansion coefficient. Furthermore, its UV filtration and hydrophobic properties would reduce perovskite decomposition and device degradation.

Researchers from Korea's Pusan National University, Gyeongsang National University, Ajou University and Switzerland's Zurich University of Applied Sciences have addressed the stability issue of perovskite solar cells (PSCs), namely the weak adhesion of C60 to perovskite layers, due to van der Waals interactions, that hinders long-term stability. 

The team developed electron-deficient intermolecular adhesives (EDIAs) as a novel interlayer material to enhance adhesion between perovskite and C60 layers. Comprehensive analyses, including density functional theory calculations, microscopy, and spectroscopy, demonstrated that EDIAs, particularly NDI-C9-Ace comprising of three key functionalities: a π-electron-deficient arene core, a hydrophobic passivation core, and a secondary-bond anchoring core, significantly improved bonding strength and recombination passivation.

Scientists at the Chinese Academy of Sciences (CAS), Xuancheng Kaisheng New Energy Technology Company and Tianjin Institute of Power Sources have found a way to make flexible tandem solar cells more efficient and durable by enhancing the adhesion of top layers to the bottom layers of the cell.

Copper indium gallium selenide (CIGS) is a commercial semiconductor known for its outstanding adjustable bandgap, strong light absorption, low-temperature sensitivity, and superior operational stability, making it a promising candidate for bottom-cell use in next-generation tandem solar cells. Flexible perovskite/CIGS tandem solar cells combine a top layer of perovskite with a bottom layer of CIGS. This tandem cell holds great potential for lightweight, high-efficiency applications in the photovoltaic field but the rough surface of CIGS makes it difficult to produce high-quality perovskite top cells on top, which limits the commercial prospects of these tandem cells.

Researchers at Queensland University of Technology (QUT) have developed an eco-friendly method to fabricate perovskite solar cells (PSCs) by incorporating a fluoride additive into a water-based solution. This approach eliminates the use of toxic solvents typically required in PSC production, while achieving power conversion efficiencies above 18%.

The team introduced lead(II) fluoride (PbF₂) into the water-based precursor solution to regulate crystal growth dynamics and improve film quality. The fluoride additive accelerated the formation of the photoactive phase and promoted the crystallization orientation, both critical for efficient solar energy conversion.

Researchers from Ulsan National Institute of Science and Technology (UNIST), Gyeongsang National University (GNU) and University of Ulsan explain that in spiro-OMeTAD-based hole-transporting layer (HTL) protocols, 4-tert-butylpyridine (tBP) is an indispensable component; however, its inclusion leads to substantial detrimental effects, hindering thermal stability. 

Recently, the team developed a tBP-free spiro-OMeTAD approach by substituting ethylene carbonate (EC) electrolyte for tBP. The electronegative carbonyl functionality led to the formation of a solvation complex with Li⁺ ions, addressing the solubility concern of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in chlorobenzene even without tBP.