Technical / research - Page 63

A team of researchers from Monash University, Wuhan University of Technology, The Hong Kong Polytechnic University, Swinburne University of Technology and Central South University has revealed defects in a popular perovskite light absorber that impede solar cell performance. The researchers found a change in the nature and density of these 'intragrain planar defects' correlated with a change in solar cell performance.

The research team used the imaging and diffraction protocol developed at the Monash Centre for Electron Microscopy (MCEM) to study the crystal structure of a range of perovskite solar cell materials in their pristine state.

An international team of researchers, including ones from Brown University, EPFL, Dalian University of Technology and Shaanxi Normal University, has developed a flexible thin-film perovskite solar cell with an efficiency of 21.0%.

The perovskite layer for the cell, which has an “n-i-p” layout, was fabricated using a metal-halide capping layer placed on top of a three-dimensional metal-halide perovskite film. This design reportedly provides hermetically sealed encapsulation, which is traditionally difficult to achieve in flexible perovskite cells, and also enhances the photocarrier properties at the interface between the perovskite film and the hole transport layer (HTL).

Researchers at the New York University (NYU) have designed a perovskite solar cell using a doping technique based on carbon dioxide (CO₂) instead of the commonly used oxygen doping approach.

The scientists described the common oxygen-based p-type doping process as one of the major hurdles to remove to bring perovskite closer to commercial production, as the technique is particularly time consuming and often requires hours to spread oxygen into a hole transporting layer of a perovskite cell.

Researchers from CHOSE (Centre for Hybrid and Organic Solar Energy) ' University of Rome 'Tor Vergata', Fraunhofer ISE and ISM-CNR have developed a full semiautomatic scalable process based on the blade-coating technique, to fabricate perovskite solar modules in ambient conditions.

An efficient and stable triple-cation cesium methylammonium formamidinium (CsMAFA) perovskite is deposited in ambient air with a two-step blading process, for the first time, by air and green anti-solvent quenching. The developed industry-compatible coating process enables the fabrication of several highly reproducible small-area cells on module size substrate with an efficiency exceeding 17% and with high reproducibility.

A team of researchers from Lund University (Sweden), the Russian Academy of Science (Russia) and the Technical University of Dresden (Germany) has developed a new methodology for the study of lead halide perovskites, based on the complete mapping of the photoluminescence quantum yield and decay dynamics in the two-dimensional (2D) space of both fluence and frequency of the excitation light pulse.

Such 2D maps not only offer a complete representation of the sample's photophysics, but also allow to examine the validity of theories, by applying a single set of theoretical equations and parameters to the entire data set.

Understanding the charge mobility of lead-halide perovskite materials is crucial for their use in photovoltaic applications. Using X-ray spectroscopic techniques, the structural deformations affecting the charge mobility, which plays a central role in solar energy conversion, have been identified and quantified by an international team of scientists led by Giulia Mancini (at the University of Pavia) and M. Chergui at EPFL.

Lead-halide perovskites' use in photovoltaic applications relies on the generation of charges (electrons and hole) upon absorption of light. These charges migrate through the material to generate an electrical current. One of the crucial physical properties in this respect is the so-called charge mobility. Despite their remarkable performances in light-to-electricity conversion, a limitation of perovskites is their charge mobilities, which are orders of magnitude smaller than those of conventional semi-conductors used in photovoltaics.

An international team of scientists from ICN2, EPFL, Eindhoven University of Technology, University of Cambridge, Max-Planck Institute for polymer Research and several other institutions have fabricated perovskite solar cells which retained almost all of their initial 21% efficiency after 1,000 hours under continuous operation at their maximum power point.

The researchers attribute this performance to an additive that ‘blocked’ ions that cause device degradation, 3-phosphono propionic acid (H3pp), which served to greatly improve device stability with no observable effects on its solar performance. The team hopes this new work will contribute to an improved understanding of the relationship between efficiency and stability in perovskite PV.

Scientists from Pennsylvania State University, Shaanxi Normal University, Hubei University and the US Army Combat Capabilities Development Command have designed a semi-transparent perovskite solar cell that reached 19.8%, and 28.3% in a tandem cell stacked on top of a silicon-heterojunction device. The device is based on a film of gold just a few atoms thick, grown using an innovative seeding method, which is both highly conductive and transparent.

The team investigated, in their new study, a new method to grow a very thin, continuous layer of gold onto a perovskite solar cell as the top electrode layer. Despite the fact that gold is a rare and expensive material, the group is convinced its approach offers an alternate, efficient route to fabricating perovskite and tandem solar cells.

Researchers from the University of Cambridge, University of Liverpool, CNRS, Indian Association for the Cultivation of Science and Diamond Light Source have shown the by melting and quenching hybrid organic'inorganic perovskite compounds, it is possible to create a new family of glasses that could find uses in the energy sector.

Comparison of physical properties of melt-quenched glasses with various materials. Image from study

The research team made three hybrid organic'inorganic perovskite compounds based on tetrapropylammonium with manganese(II), iron(II) and cobalt(II) and melted them. According to author François-Xavier Coudert at the CNRS in France, they had to tune the temperature to aim for a very narrow temperature window, around 20 degrees on average, depending on each metal used ' hot enough to liquefy the samples, but not so hot that it decomposes them. The team measured the exact heat coming in and out of the glasses to learn their properties, describing each one thoroughly. 'We're melting a novel class of materials and accessing a novel family of glasses,' Coudert says. 'I've probably never seen materials so well characterized with so many techniques and so much information. It is fascinating to see all of these methods together.'

Researchers at the University of Sheffield have found that storing perovskite precursor solutions at low temperatures extends their operational lifetime from under a month to over four months.

Understanding how to make perovskite solutions more durable and reliable could potentially make the manufacture of perovskite solar cells more efficient, as the process would require fewer batches of more stable material to be produced, saving time, reducing material waste and also allowing device yield and efficiency to be optimized.