From the labs. Solar cell with 24.8% efficiency?

In the world of solar photovoltaic cells, even a single point change to the right of the decimal is big. With conventional solar cells, you’d be lucky if you convert 20 per cent of the light energy that falls on them into electric energy. The number is said to be better with perovskite solar cells, which are made with materials in which atoms are arranged in a particular manner. But perovskite cells are not stable, so they don’t last long. Research is afoot globally to produce a stable perovskite solar cell that is economically viable.

Now a group of Chinese researchers have claimed they have produced a perovskite solar cell with an efficiency of 24.8 per cent. In a paper published in the Joule magazine, Hao Huang et al credit it to “ligand-engineered deposition strategy”. They claim to have achieved “an impressive power conversion efficiency of 24.8 per cent with a fill factor (a measure of the quality of the module) of 0.83”. But what of stability? They “can maintain 95 per cent of initial efficiency on exposure to ambient air for 2,000 hours”.

Gallium from fly ash

Fly ash from coal-fired power plants is a nuisance and disposing of it safely is a challenge. Some fly ash goes into manufacturing bricks, but that is very little.

Now, the Indira Gandhi Centre for Atomic Research and the Bhabha Atomic Research Centre claim they could determine the concentration of gallium — a metal with wide applications in strategic fields such as communications and satellite broadcast — in fly ash.

In a paper published in Applied Radiation and Isotopes, Manish Chant et al say the gallium content in the fly ash samples of the bituminous coal collected from south-central and eastern India was found to be 17.2-47.9 mg/kg while it was 6.3–33.3 mg/kg for samples of lignite coal collected from south-central and western India. The researchers used a technique called ‘neutron activation analysis’ (bombarding a material with neutrons to convert some atoms into radioactive materials). The samples of coal ash “proved to be a potential source of gallium,” the paper says.

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Stronger, lighter concrete

Scientists at the Department of Civil Engineering, Visvesvaraya National Institute of Technology (VNIT), Nagpur, have developed a modular toilet unit cast with geopolymer concrete (GPC), incorporating industrial wastes. In a paper published in Case Studies in Construction Materials, Sandeep Tembhurkar et al say the toilets are easy to install, scalable and durable.

The density of GPC is 92.9 per cent of the density of conventional concrete, which makes it lighter and easier to install. The compressive strength is 32MPa, which is 148.6 per cent higher than conventional units. Flexural strength is 209 per cent higher with the use of crushed sand in wall panels, slab, and foundation, and steel fibres in wall panels. Water absorption is 86.6 per cent of that in conventional units.

The central and state governments provide assistance of about ₹14,000 per toilet unit under the Swachh Bharat Abhiyan programme. With GPC there is savings of about ₹1,600 per toilet, the paper says.

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