Not so long ago, all batteries were single use. And solar power was an emerging and expensive technology. Now, thanks to rechargeable batteries, we have mobile phones, laptops, electronic toys, cordless power tools and other portable electronic devices. And solar power is reducing our reliance on carbon-based fossil fuels. None of this would have been possible without a deep understanding of the chemistry of materials that have particular properties – the ability to turn sunlight into energy for example. Professor Saiful Islam of the University of Bath tells Jim Al-Khalili how ‘the Woodstock of physics’ got him excited about material science and how his research on the properties of materials is helping to power the 21st century with renewable energy and could dramatically reduce the cost of making solar panels.