Science closer to solar-powered 'artificial leaves'

Artificial leaves and nano-forests that can efficiently harvest the sun’s light energy might sound like a pipe dream, but an international team of researchers say they’ve achieved the first step toward that goal.

The team modified chlorophyll from an alga to resemble the extremely efficient light antennae of bacteria, and then was then able to determine the structure of these light antennae. The research findings will be published next week in the online Early Edition of the PNAS journal.

In theory, artificial “forests” at a nano scale and pavements laced with pigment molecules that collect sunlight could harvest the sun’s energy and easily convert it into clean power. Before this can happen, however, scientists must first develop artificial photosynthesis systems that work both quickly and efficiently.

Two things are needed to generate fuel from sunlight: an antenna that harvests light, and a light-driven catalyst. The article in PNAS is about the first of these: the antenna.

The fastest light harvesters are found in nature: in green leaves, algae and bacteria. The light antennae of bacteria — chlorosomes — are the fastest of all. They have to be capable of harvesting minimal quantities of light particles in highly unfavourable light conditions, such as deep in the sea. These chlorosomes are made up of chlorophyll molecules.

A team led by University of Leiden researcher Huub de Groot modified chlorophylls from the alga Spirulina to resemble the pigments of bacteria. The group then studied the structure of these semi-synthetic light antennae.

“We already knew that the light antennae in bacteria form a structure rather like the annual rings of a tree trunk,” said De Groot. “The molecules in these semi-synthetic antennae seem to stack in a different way; they are flat. But this, too, is one of four ways we had thought in advance were possible.”

The researchers still have to determine how the light antennae of modified Spirulina chlorophylls work in practice.

“This is a completely new approach in this field,” said De Groot.