Technical / research - Page 56

Researchers at the National Renewable Energy Laboratory (NREL), along with collaborators from the SLAC National Accelerator Laboratory, University of Toledo, Princeton University, University of Arizona, University of Kentucky, and University of Colorado, have found away to improve the efficiency of perovskite solar cells by as much as 16%.

The effort involved combining a two-dimensional (2D) perovskite layer with a three-dimensional (3D) perovskite layer, which yielded a solar cell with improvements in both efficiency and stability.

Recent research has shown that the incorporation of graphene-related materials improves the performance and stability of perovskite solar cells. Graphene is hydrophobic, which can enhance several properties of perovskite solar cells. Firstly, it can enhance stability and the passivation of electron traps at the perovskite's crystalline domain interfaces. Graphene can also provide better energy level alignment, leading to more efficient devices.

In a recent study, Spain-based scientists used pristine graphene to improve the properties of MAPbI₃, a popular perovskite material. Pristine graphene was combined with the metal halide perovskite to form the active layer of the solar cells. By analyzing the resulting graphene/perovskite material, it was observed that an average efficiency value of 15% under high-stress conditions was achieved when the optimal amount of graphene was used.

Researchers from Rice University and collaborators from Purdue and Northwestern universities, U.S. Department of Energy national laboratories Los Alamos, Argonne and Brookhaven and the Institute of Electronics and Digital Technologies (INSA) in Rennes, France, have reached a new benchmark in the design of atomically thin solar cells made of semiconducting perovskites, boosting their efficiency while also focusing on their stability.

The lab of Aditya Mohite of Rice's George R. Brown School of Engineering discovered that sunlight itself contracts the space between atomic layers in 2D perovskites enough to improve the material's photovoltaic efficiency by up to 18%.

Researchers from the University of Cambridge, in collaboration with Cambridge's Cavendish Laboratory, the Diamond Light Source synchrotron facility in Didcot and the Okinawa Institute of Science and Technology in Japan, have used a suite of correlative, multimodal microscopy methods to visualize, for the first time, why perovskite materials are seemingly so tolerant of defects in their structure.

The impressive performance of perovskites is surprising, as the typical model for an excellent semiconductor is a very ordered structure, but the array of different chemical elements combined in perovskites creates a much 'messier' landscape. This heterogeneity causes defects in the material that lead to nanoscale 'traps', which reduce the photovoltaic performance of the devices. But despite the presence of these defects, perovskite materials still show efficiency levels comparable to their silicon alternatives. In fact, earlier research by the same group has shown the disordered structure can actually increase the performance of perovskite optoelectronics, and their latest work seeks to explain why.

Researchers from various universities and laboratories around the world have recently melted metal-organic frameworks (MOFs) and mixed them with perovskites to yield highly stable luminescent composites. The mixtures reportedly resist exposure to heat, air, and humidity.

Lead-halide perovskites, such as cesium lead iodide, naturally exhibit photoluminescence, says chemist Thomas D. Bennett of Cambridge University and the paper's lead author. 'However, this light-emitting phase is only stable at high temperatures, and its effects disappear when the material cools down,' he adds. In the new work, researchers preserved this photoluminescence using MOF glasses to trap this metastable phase at room temperature and, at the same time, encapsulate and protect the perovskite.

A group of scientists, led by Prof. Yiqiang Zhan from Fudan University, has reported high-efficiency flexible perovskite solar cells (f-PSCs) by annealing a SnO₂ ETL in a rough vacuum at a low temperature (100 '), and peak efficiency reached 20.14%.

SnO₂ layers that have been prepared by this method have shown higher robustness and hydrophobicity in comparison with samples prepared in an air atmosphere and temperatures of 100 °C, leading to an improved ETL/perovskite interface connection and reducing defects in the SnO₂/perovskite interface. The appropriate density of oxygen vacancies on the surface during this treatment can be responsible for higher conductivity, which is beneficial for charge transfer.

Researchers from Korea, led by Prof. Bongjin Simon Mun from Gwangju Institute of Science and Technology, have used ambient pressure X-ray photoelectron spectroscopy (AP-XPS) and low energy electron diffraction (LEED) to investigate how fabrication conditions (annealing in an oxygen-rich environment and an oxygen deficit, low-pressure environment) for a particular perovskite material, SrTiO₃, affects its undoped surface and the resulting interfacial layer of the heterostructure.

Certain perovskites can be promising alternatives to silicon-based components for next generation electronic applications. Their structure makes them ideal for use as a base for growing oxide films to form heterostructures with unique electrical properties. The properties of these heterostructures depend on the charge transfer in the interfacial layer between the perovskite substrate and oxide overlayer. This charge transfer can be manipulated via either doping or through the fabrication process.

Scientists from Japan's Kishu Giken Kogyo and University of Hyogo, Switzerland's Solaronix and Germany's Fraunhofer ISE have examined the long-term stability of perovskite solar cells using layers of mesoporous carbon, building on previous work that showed the strong potential of this approach.

Schematics of reversible light-induced performance increase for m-CPSM. Image from study

This recent work demonstrated a light-soaking effect, which allowed them to fabricate cells that retained 92% of their initial performance after 3,000 hours in damp heat conditions – which the researchers say is equivalent to 20 years in the field.

Researchers at the Dutch Organization for Applied Scientific Research and Eindhoven University of Technology in the Netherlands have recently used a solution-processed photodetector made of a metal halide perovskite to fabricate a thin and flexible scanner. This scanner can be used to scan both fingerprints and paper documents.

"Fabricating photodetectors with low dark currents and integrating them into high-resolution backplanes remains challenging," Albert J. J. M. van Breemen and his colleagues wrote in their paper. "Here, we show that solution-processed metal halide perovskite photodiodes on top of an amorphous indium gallium zinc oxide transistor backplane can be used to create a flexible image sensor that is ~100'μm thick and has a resolution of 508 pixels per inch."

In October 2021, The Perovskite-Info team met Cyprus University of Technology's (CUT) Professor Stelios Choulis, who kindly agreed to show us around his workspace and labs and update us on his team's ongoing work.

Choulis, Professor of Material Science and Engineering at the Cyprus University of Technology, is also the founder and head of the Molecular Electronics and Photonics (MEP) Research Unit. With work in UK, Germany and the Silicon Valley (USA) under his belt, Choulis is a highly skilled and experienced researcher in the fields of both photovoltaics and OLEDs. He also participated and led several large-scale research programs (ERC-Consolidator Grant European Horizon project, SME-EU FP7, RIF and RPF-Cyprus, BMBF-Germany, DOE-USA).