Technical / research

Miniaturizing LEDs is crucial for creating ultra-high-resolution displays. Metal-halide perovskites show potential for efficient light emission, long-distance carrier transport, and scalable production of bright micro-LED displays. However, current thin-film perovskites face issues with uneven light emission and surface instability during lithography, making them unsuitable for micro-LED devices. There's a strong need for continuous single-crystal perovskite films with minimal grain boundaries, stable surfaces, and uniform optical properties for micro-LEDs. Yet, growing these films and integrating them into devices remains a challenge.

Remote epitaxial crystalline perovskites for ultrahigh resolution micro-LED displays. Image credit: Chinese Academy of Sciences

Recently, researchers from the Chinese Academy of Sciences, University of Science and Technology of China and Jilin University made significant progress in this field. The team developed a novel method for the remote epitaxial growth of continuous crystalline perovskite thin films, that allows for seamless integration into ultrahigh-resolution micro-LEDs with pixels less than 5 μm.

Researchers from China's Wuhan University and Hubei University have examined the long-term stability problem of tin-lead perovskites under irradiation, counterintuitively discovering an irreversible phase reconstruction process. 

The evolution from tin-lead perovskites to a reconstruction of lead perovskites under light. Image from: Nature Communications

Tin-lead perovskite materials show promise for all-perovskite tandem solar cells, offering an optimal bandgap that significantly boosts power conversion efficiency. However, light-induced degradation, particularly in ambient air, remains a major obstacle to their long-term stability. Unlike single-metal perovskite materials, tin-lead perovskite degrades through distinct mechanisms, making it crucial to understand how it deteriorates under light and air exposure.

Researchers from the University of Twente, Academy of Sciences of the Czech Republic, AMOLF, Universidad Andres Bello and University of Oxford have developed a way to create highly ordered semiconductor material at room temperature, that could make optoelectronics more efficient by controlling the crystal structure and reducing the number of defects at the nanoscale.

The team focused on metal halide perovskites. Making these materials with one single orientation (or in other words with highly ordered grains) has been a challenge and thus far, they have mainly been used in the non-ordered polycrystalline form. This can limit their use in applications such as LEDs, where high order and low density of defects are needed. Normally, these highly ordered semiconductors require high processing temperatures. But in this new process, the researchers skip the heat and build up the material layer by layer using a pulsed laser.

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%. 

Hybrid perovskites show piezoelectric properties due to polarization and centro-symmetry breaking of PbX₆ pyramids (X = I^-, Br^-, Cl^-). Researchers from The Hebrew University of Jerusalem, Polish Academy of Sciences and Nanyang Technological University recently examined the piezoelectric response of quasi-2D perovskites using various barrier molecules: benzyl amine (BzA), phenylethyl amine (PEA), and butyl diamine (BuDA).

Utilizing piezoelectric force microscopy measurements, the team determined the piezoelectric coefficient (d33) where BuDA exhibits a substantial response with values of 147 pm V^–1 for n = 5, better than the other quasi-2D and 3D perovskite counterparts. Density functional theory calculations revealed distorted bond angles in the PbBr₆ pyramids for quasi-2D perovskites, enhancing symmetry breaking. 

Researchers from China's Xi’an Jiaotong University, Huazhong University of Science and Technology, Fudan University, ULVAC-PHI Instruments, National University of Singapore (NUS), Sweden's Uppsala University and EPFL have developed a self-assembled bilayer (SAB) that can be used as a hole contact material that grants improved adhesive contact with the perovskite film. 

A schematic illustration of the inverted PSCs. Image from: Nature Energy

The team went on to fabricate an inverted perovskite solar cell that utilizes the self-assembled bilayer (SAB) as a hole-selective molecular contact. The cell was made with a substrate made of glass and transparent conductive oxides (TCOs), the proposed bilayer, the perovskite absorber, an ETL based on buckminsterfullerene (C60), a bathocuproine (BCP) buffer layer, and a silver (Ag) metal contact. 

Researchers from EPFL and CSEM recently fabricated efficient (>20 %) and stable (T80 ∼ 720 h) planar FAPbI₃-based perovskite (1.54 eV) solar cells via a hybrid evaporation-spin coating process. 

FAPbI₃-based perovskite films were fabricated via a hybrid two-step evaporation-spin coating method in an inverted (p-i-n) configuration, and the effects of optimized parameters on the film growth and devices’ performances were investigated. Transferring these films into tandem devices atop single-side textured silicon heterojunction bottom cells, the team obtained an efficiency of >24 % under AM1.5 G illumination for monofacial devices with an active area of 1.21 cm². Furthermore, the bifacial devices generated >27 mW cm⁻² power output with 15 % rear illumination fraction.

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 The Hong Kong Polytechnic University, Beijing Institute of Technology and University of California Los Angeles have addressed the fragile and moisture-sensitive nature of halide perovskite materials by using an asynchronous cross-linking strategy. 

Schematic illustration of intermediate-dominated perovskite crystallization by pre-embedded DVS and all-around co-polymerization protection through the post-treatment of gly. Image credit: Nature Communications

A multifunctional cross-linking initiator, divinyl sulfone (DVS), is firstly pre-embedded into perovskite precursor solutions. DVS facilitates intermediate-dominated perovskite crystallization manipulation, favoring formamidine-DVS based solvate transition. Subsequently, DVS-embedded perovskite as-cast films are post-treated with a nucleophilic reagent, glycerinum, to trigger controllably three-dimensional co-polymerization. The resulting cross-linking scaffold provides enhanced water-resistance, releases residual tensile strain, and suppresses deep-level defects.