Print flexible solar cells

he future of solar energy depends on a union of new and old technologies. If photovoltaic (PV) devices that turn light into electricity could be mass produced with printing presses, as if they were news papers or banknotes, they could be affordable and ubiquitous. Conventional, silicon-based, solar panels are rigid and bulky. Small, thin and flexible PV devices on films are already being made that are lightweight and translucent. These use little material and can generate electricity in low light, even indoors. Integrating them into phones and watches, as well as walls and windows, would transform the world's energy generation, reduce pollution and mitigate climate change. Yet flexible solar panels face several hurdles. Some are based on harmful substances such as heavy metals, and their manufacture uses hazardous solvents. Others are quick to degrade and inefficient at converting light into electricity. Printers used in the publishing, computing and electronics industries struggle to print PV materials that need to be built with nano-metre precision over many square metres. For all these reasons, printable solar cells are yet to find a foothold in electricity markets. Most research and development investment goes into conventional silicon solar cells, which account for more than 90% of global production. Yet manufacturing these uses a lot of energy: equivalent to about 10% of the cell's lifetime output 1. Printed solar cells won't become widespread until they are cheaper and safer to make. Researchers and businesses must work together to improve the efficiency, environmental impact and stability of these cells, scale up their manufacture and plan their market penetration. Mass production at low cost is what the solar industry sorely needs. The power that a PV panel generates is proportional to the surface area exposed to sunlight. The world consumes approximately 20,000 terawatt-hours of electricity each year 2. Meeting this need would require enough PV devices to cover around 100,000 square kilometres, an area about the size of Iceland. Such production rates have yet to be achieved. Printed PV devices are typically made from many layers of material on a substrate of conductive glass or plastic. Each layer has a function: semi conductors or sensitizers absorb visible light, and other materials carry electrical charges to electrodes. Many types of printed PV device are being developed. Some feature organic s emiconductors such as polythiophenes. Others use light-absorbing dyes, including ruthenium-based polypyridines. And in quantum-dot solar cells, nano-particles absorb light. …