Stability

Researchers at South Korea’s Chonnam National University have reported perovskite-organic hybrid tandem solar cells with 23.07% efficiency processed entirely in open air, bringing the technology a step closer to economic viability.

Schematic illustration of the synthesis of all-inorganic perovskite thin films by dynamic hot-air-assisted method. Image from Energy & Environmental Science 

Researchers have largely relied on meticulously engineering the perovskite crystal structure itself for greater resilience. But these delicate handling steps add cost and complexity not suitable for mass production. The team explained that the focus has recently shifted toward all-solution processed solar cells due to their low energy consumption fabrication processes. The team’s innovation, a dynamic hot air deposition technique, simplified the production process by eliminating the need for humidity-controlled environments.

Researchers in Sweden and China have studied the reasons behind the short operational lifetime of blue perovskite-based LEDs (PeLEDs). 

While perovskite light-emitting diodes (PeLEDs) have seen unprecedented development in device efficiency over the past decade, they still suffer from poor operational stability. This is especially true for blue PeLEDs, whose operational lifetime remains orders of magnitude behind their green and red counterparts. The scientists in this work have systematically investigated this efficiency-stability discrepancy in a series of green- to blue-emitting PeLEDs based on mixed Br/Cl-perovskites. Typically, mixed chloride/bromide perovskites are employed to produce ideal blue emission. However, the researchers have uncovered a counterintuitive fact: even minute quantities of chloride loading can have a dramatic negative impact on the operational lifetime of these devices. 

Researchers of Karlsruhe Institute of Technology (KIT) and of two Helmholtz platforms—Helmholtz Imaging at the German Cancer Research Center (DKFZ) and Helmholtz AI—have found a way to predict the quality of the perovskite layers and consequently that of the resulting solar cells. Using machine learning and new methods in artificial intelligence (AI), it is possible to assess their quality from variations in light emission already in the manufacturing process.

"Manufacturing these high-grade, multi-crystalline thin layers without any deficiencies or holes using low-cost and scalable methods is one of the biggest challenges," says tenure-track professor Ulrich W. Paetzold who conducts research at the Institute of Microstructure Technology and the Light Technology Institute of KIT.

Researchers at China's Wuhan University assume that the practical use of all-perovskite tandem solar cells is hampered by the subpar performance and stability issues associated with mixed tin–lead (Sn–Pb) narrow-bandgap perovskite subcells. In their recent study, they focus on these narrow-bandgap subcells and develop an all-in-one doping strategy for them. 

The scientists introduce aspartate hydrochloride (AspCl) into both the bottom poly(3,4-ethylene dioxythiophene)–poly(styrene sulfonate) and bulk perovskite layers, followed by another AspCl posttreatment. They show that a single AspCl additive can effectively passivate defects, reduce Sn⁴⁺ impurities and shift the Fermi energy level. 

Researchers at the Chinese Academy of Sciences (CAS), Beijing Normal University, Beijing Institute of Technology and ShanghaiTech University have developed a universal hydrogen-bonding-facilitated DMA extraction method to fabricate high-quality γ-CsPbI3 films. The researchers fabricated a solar cell based on cesium-lead iodide (CsPbI₃) perovskite, which is also known as black perovskite.

The black perovskite solar cell reportedly achieved  20.25% efficiency, which is said by the team to be the highest efficiency reported for PV devices built with this perovskite material and a dopant-free hole transport layer based on the P3HT polymer. The cell was also able to retain around 93% of its original efficiency after continuous illumination for 570 h.

Inverted perovskite solar cells (PSCs) can deliver enhanced operating stability compared to their 'normal'-structure counterparts. To improve efficiency further, it is vital to combine effective light management with low interfacial losses. Now, scientists at Northwestern University, University of Kentucky, North Carolina State University, University of Toronto, Ecole Polytechnique Fédérale de Lausanne (EPFL) and Peking University have developed a conformal self-assembled monolayer (SAM) as the hole-selective contact on light-managing textured substrates. 

The team reported that molecular dynamics simulations indicate cluster formation during phosphonic acid adsorption leads to incomplete SAM coverage. They devised a co-adsorbent strategy that disassembles high-order clusters, thus homogenizing the distribution of phosphonic acid molecules, thereby minimizing interfacial recombination and improving electronic structures.

In an effort to tackle the challenge of perovskite solar cells' thermal instability, researchers at City University of Hong Kong (CityU), National Renewable Energy Laboratory (NREL) and Huazhong University of Science and Technology have developed a unique type of self-assembled monolayer, or SAM for short, and anchored it on a nickel oxide nanoparticles surface as a charge extraction layer. This method dramatically enhanced the thermal robustness of perovskite solar cells, according to Professor Zhu Zonglong of the Department of Chemistry at CityU.

“By introducing a thermally robust charge extraction layer, our improved cells retain over 90% of their efficiency, boasting an impressive efficiency rate of 25.6%, even after operated under high temperatures, around (65℃) for over 1,000 hours. This is a milestone achievement,” said Professor Zhu.

Existing fabrication processes for creating efficient metal halide perovskite solar cells (PSCs) require an inert (i.e., chemically inactive) atmosphere, such as that within a nitrogen glovebox. Recently, researchers from China's North China Electric Power University have introduced a strategy to create PSCs with PCEs above 25% in ambient air. 

This strategy is hoped to accelerate commercialization of PSCs. "The fabrication of perovskite solar cells (PSCs) in ambient air can accelerate their industrialization," Luyao Yan, Hao Huang and their colleagues wrote in their paper. "However, moisture induces severe decomposition of the perovskite layer, limiting the device efficiency. We show that sites near vacancy defects absorb water molecules and trigger the hydration of the perovskite, eventually leading to the degradation of the material." To fabricate their solar cells in ambient air conditions, the scientists blocked the pathway through which perovskite layers can become hydrated and consequently suffer severe damage. They did this using the acetate salt form of the chemical compound guanabenz, known as GBA.

This is a sponsored post by Ergis Group

In 2020, Poland-based Ergis Group launched the noDiffusion film platform, a high-barrier film that offers high level of optical transmittance and low level of light scattering, and the ability to contain transparent conductive electrodes. The new technologies adopted in the production of the barrier films offer a combination of high performance and competitive pricing.

Following years of R&D, Ergis is ready to enter production with its first-gen barrier films, produced using sputtering in a roll-to-roll (R2R) configuration. The company reports performance of around 10^-4 wtr performance for its barrier. This is referred to as a "light-barrier" and one that is more than enough for the encapsulation of perovskite materials. The company collaborated with Poland-based Saule Technologies to develop this specific film. Ergis is now shipping barrier film samples to its customers.

Researchers at the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) and the University of Toledo have found that perovskite solar cells should be subjected to a combination of stress tests simultaneously to best predict how they will function outdoors.

The team used a state-of-the-art p-i-n PSC stack (with PCE up to ~25.5%) to show that indoor accelerated stability tests can predict 6-month outdoor aging tests. Device degradation rates under illumination and at elevated temperatures are most instructive for understanding outdoor device reliability. The team also found that the indium tin oxide (ITO)/self-assembled monolayer (SAM)-based hole transport layer (HTL)/perovskite interface most strongly affects the device operation stability. Improving the ion-blocking properties of the SAM HTL increases averaged device operational stability at 50°C–85°C by a factor of ~2.8, reaching over 1000 h at 85°C and to near 8200 h at 50°C with a projected 20% degradation, which is among the best to date for high-efficiency p-i-n PSCs.