Technical / research - Page 6

An international team of researchers, including ones from the University of Sydney, IEK-5 Photovoltaics at Forschungszentrum Jülich, Southern University of Science and Technology, UNSW and the University of Ljubljana, recently reported the use of a piperidinium bromide (PpBr) as an interlayer between C60 and perovskite. The interlayer was further optimized by introducing an additional oxygen atom on the opposite side of the NH²⁺. 

The tandem structure that the team used for demonstrations. Image credit: Advanced Energy Materials

This reportedly resulted in morpholinium bromide (MLBr) with increased dipole moment. Because of this, MLBr was highly effective in minimizing the energy band mismatch between perovskite and C60 layer for electron extraction while at the same time passivating defects. 

Researchers from Shenzhen University recently addressed the stability issue of organic–inorganic hybrid perovskites, which the team says is currently a barrier to their widespread commercial application in optoelectronic devices. In addition to enhancing perovskite stability, the real-time detection of aging status, aimed at monitoring the aging progression, holds paramount importance for both fundamental research and the commercialization of organic–inorganic hybrid perovskites.

Schematic diagram of the THz-TDS system. Image from:  Frontiers of Optoelectronics 

In their recent work, the team examined the aging status of perovskite in real-time by using terahertz time-domain spectroscopy. This technique is based on the resonant absorption of terahertz waves by phonons in the perovskite. As perovskites age, the intensity of phonon vibration modes associated with the Pb-I bonds decreases, leading to changes in the absorption peaks of terahertz waves at specific frequencies. Based on this, they proposed using the intensity of these terahertz absorption peaks as an indicator to measure the ageing degree of perovskites in real-time.

As the area of perovskite films and devices increases, their performance tends to deteriorate - which researchers from the Chinese Academy of Science (CAS), University of Science and Technology of China and Dalian University of Technology explain can be linked to defects that accumulate at the bottom surface without proper passivation. In an attempt to address this issue, the team introduced a unique molecule (1-(4-Fluorophenyl)−2-pyrrolidone, or FPP) as an additive in large-area blade-coating perovskite films. 

During the top-down crystallization process, the FPP molecule forms an intermediate phase with the perovskite components and subsequently self-deposits at the bottom surface. Consequently, the crystallization kinetics of the large-area thin films are regulated, and the bottom surface is effectively and uniformly passivated in one single-step processing. 

Perovskite crystals, with their exceptional nonlinear optical properties, lasing and waveguiding capabilities, could offer a promising platform for integrated photonic circuitry within the strong-coupling regime at room temperature.

Researchers at the University of Warsaw, CNR Nanotec, Łukasiewicz Research Network—Institute of Microelectronics and Photonics, Łódź University of Technology and Polish Academy of Sciences have demonstrated a versatile template-assisted method to efficiently fabricate large-scale waveguiding perovskite crystals of arbitrarily predefined geometry such as microwires, couplers and splitters. 

BusinessKorea reports that researchers at the Ulsan National Institute of Science and Technology (UNIST) have significantly improved the efficiency and stability of perovskite solar cells by addressing defect issues.

Schematic of perovskite crystallinity changes and thickness-based photoluminescence analysis through the introduction of bidirectional tuning molecules. Source: BusinessKorea, UNIST

The UNIST team announced that a joint research team, led by Professors Kim Jin-young and Kim Dong-seok from the Department of Energy and Chemical Engineering, and Professor Lee Geun-sik from the Department of Chemistry, successfully introduced bidirectional tuning molecules between the perovskite photoactive layer and the electron transport layer.

An international team of researchers, including ones from the University of Toronto, University of Toledo, Northwestern University, Lawrence Berkeley National Laboratory, KAUST and more, recently developed an all-perovskite tandem device that is said to show reduced recombination losses in the cell’s bottom device and excellent stability.

Image credit: Northwestern University
 

To improve the perovskite solar cell’s surface, the scientists created partially non-conductive and non-functional areas that protect the perovskite area underneath from becoming defective. The team examined the addition of diamine to improve the perovskite solar cell’s surface. The scientists found that the process made the surface more stable and improved the overall performance, resulting in a power conversion efficiency of 27.4% with better stability.

Researchers from China's Beijing Institute of Technology, Peking University, Central South University, Jiangnan University and Auner Technology have developed a unique binary 2D perovskite passivation approach and used it to fabricate a monolithic perovskite/silicon tandem solar cell with a steady-state efficiency of 30.65% (reportedly assessed by a third party). 

Schematic of the monolithic tandem structure based on a double-side textured silicon heterojunction cell. Image credit: Nature Communications

The tandem devices also retained 96% of their initial efficiency after 527 h of operation under full spectral continuous illumination, and 98% after 1000 h of damp-heat testing (85 °C with 85% relative humidity).

Colloidal perovskite nanoplatelets (NPLs) have shown promise in tackling blue light-emitting diode challenges based on their tunable band gap and high photoluminescence efficiencies. However, high quality and large area dense NPL films have been proven quite hard to prepare due to their chemical and physical fragility during the liquid phase deposition.

Recently, researchers from University of Groningen reported a perovskite-polymer composite film deposition strategy with fine morphology engineering obtained using the blade coating method. The effects of the polymer type, solution concentration, compounding ratio and film thickness on the film quality were systematically investigated and the team found that a relatively high-concentration suspension with an optimized NPL to polymer ratio of 1 : 2 is crucial for the suppression of phase separation and arriving at a uniform film.

Metal halide perovskite light-emitting diodes (PeLEDs) that emit deep-blue color with high efficiency have not yet been fully achieved and become more difficult in the thin film of confined perovskite colloidal quantum dots (PeQDs) due to particle interaction. Recently, researchers from Seoul National University and University of Toronto demonstrated that electronic coupling and energy transfer in PeQDs induce redshift in the emission by PeQD film, and consequently hinder deep-blue emission.

Scheme illustrating QD-QD interaction related to emission spectrum shifts in the A) QD-only film and B) QD-mCP solid solution. Image credit: Advanced Materials

To achieve deep-blue emission by avoiding electronic coupling and energy transfer, a QD-in-organic solid solution was introduced, to physically separate the QDs in the film. This physical separation of QDs reduces the interaction between them yielding a blueshift of ≈7 nm in the emission spectrum. 

Researchers from Queen Mary University of London and QinetiQ could pave the way for faster discovery of novel perovskite materials with desirable properties for applications in wireless communication and biosensors. The recent research introduces an automated platform for rapid sintering and dielectric characterization of perovskite solid solutions. This innovative approach integrates machine learning (ML) for material screening with robotic synthesis and high-throughput characterization.

The scientists stated that while accelerating perovskite solid solution discovery and sustainable synthesis is crucial for addressing challenges in wireless communication and biosensors, the vast array of chemical compositions and their dependence on factors such as crystal structure and sintering temperature require time-consuming manual processes. To overcome these constraints, they introduced an automated materials discovery approach encompassing machine learning (ML) assisted material screening, robotic synthesis, and high-throughput characterization.