Sunshine the energy of the future

Solar cells that are incorporated into roofing materials and provide all the energy used in a home or office building could become an affordable option in New Zealand within a decade says a leading researcher in the field.

Although solar cells have been available for many years, uptake has been limited by their cost says Dr Justin Hodgkiss, a lecturer in Victoria’s School of Chemical and Physical Sciences.

That’s because conventional solar cells use silicon to absorb light and convert the energy into electricity, and processing silicon into a working solar cell is very expensive.

Dr Hodgkiss was recently awarded a Rutherford Discovery Fellowship providing financial support of $160,000 per year over five years to investigate this area further.

He is one of a number of scientists in New Zealand and overseas who are investigating an alternative option of making solar cells from polymers or plastics. They are building on the work of Nobel Prize winning New Zealand scientist and Victoria alumnus Alan MacDiarmid who discovered the electronic conductivity of polymers.

Dr Hodgkiss says the major advantage of using polymers is that they can be dissolved to make an ink and then printed in sheets

"That opens the possibility of making them quite cheaply. We might even be able to use existing machinery—in Australia, they are experimenting with printing polymer solar cells on the same presses used to print money."

The resulting solar cells would have a few layers made up of films of an active polymer sandwiched between transparent electrodes. "It sounds complicated but it’s not very different from a potato chip bag."

Polymer solar cells are currently less efficient than those using silicon but that is changing.

"Four years ago when I started working in this field," says Dr Hodgkiss, "polymer solar cells had a power conversion efficiency of four per cent and it’s now eight per cent (different types of silicon cells are between 10 and 20 per cent) so it’s on a steep trajectory."

He estimates that if every New Zealand rooftop was covered in a material containing a 10 per cent efficient solar cell, that would easily generate all of New Zealand’s energy needs.

Dr Hodgkiss and the PhD and Masters students working with him are focusing on what happens in the first femtoseconds (one millionth of one billionth of a second) when the light absorbed by polymers begins generating free charges to flow as electricity.

"What makes that happen is still a mystery. If we can find out why, we can design materials that will encourage more electrons to break free and we will end up with more energy."

The work, called ultra fast spectroscopy, involves taking ultra precise measurements using highly specialised laser tools and is being done in a specially built laboratory at Victoria.

Scientists working on related light-based technologies will also be able to use the lab.

Dr Hodgkiss, who is a Principal Investigator at the MacDiarmid Institute for Advanced Materials and Nanotechnology, says a range of other research projects in New Zealand are also delivering new knowledge that will help make solar energy a viable option.

That includes developing quantum dot solar cells that can harvest more sunlight, printable nano-structured plastics that will improve the efficiency of solar cells, and creating new molecules to optimise the performance of polymer solar cells.

Dr Hodgkiss says he was motivated to study in his research field because of the pressing need to find new, clean and sustainable sources of energy.

"Solar energy is such an untapped resource and one that could easily meet global energy demands if properly harnessed.

"It’s also promising for New Zealand. The fabrication process for polymer solar cells is so simple, there is no reason we can’t do it here."