CHICAGO - US researchers have found a way to make efficient silicon-based solar cells that are flexible enough to be rolled around a pencil and transparent enough to be used to tint windows on buildings or cars.

Hundreds more people could die because of increasing levels of ozone at street level, according to scientists.

A study by the Royal Society found ground levels of ozone, the pollutant caused when sunlight hits a mixture of gases in the air, has risen by six per cent per decade since the 1980s.