Spinach power for solar cells | Science News for Students

Spinach power for solar cells

A solar cell based on chemicals taken from spinach and bacteria converts light into electricity.
Jun 9, 2004 — 5:37 pm EST
a bunch of spinach growing in dirt

Chemical substances extracted from spinach are among the ingredients needed for making a solar cell that converts light into electricity.


Popeye uses spinach to power his muscles. Now, scientists are looking to spinach as a power source for making electricity.

A solar cell converts sunlight into electricity. Most of these, today, are made of a material called silicon. The new device instead uses proteins from spinach and from a bacterium called Rhodobacter sphaeroides.

To make the solar cell, a team of biologists and chemists at the Massachusetts Institute of Technology in Cambridge extracted certain light-sensitive proteins from the spinach and the bacteria. They placed about 2 billion of these proteins on a piece of glass. They made the proteins stick by embedding them in a special framework that looks and acts like a cell membrane.

The researchers then samdwiched the layer of proteins between layers of other materials called semiconductors. Those other materials carry electricity. Then the scientists shone certain types of light on the device.  The proteins absorbed the light and sent electrons through the semiconductor to an electrode. This activity caused an electric current to flow.

In this solar cell, light-sensitive proteins obtained from spinach and bacteria (yellow spheres) absorb light and pump electrons (e<sup>–</sup>) into a silver electrode.

In this solar cell, light-sensitive proteins obtained from spinach and bacteria (yellow spheres) absorb light and pump electrons (e) into a silver electrode.

Courtesy of Marc Baldo, Massachusetts Institute of Technology

At this early stage in the research, the spinach cell isn't efficient enough to be useful. To improve their solar cell, the researchers want to jam more proteins into a single device. They also want such solar cells to stay active for a long time. One hope is that protein-based solar cells might repair themselves, just like living plants replace their own proteins over time.

If it all works out, there may be a new way to harvest the sun's energy. Instead of just eating your spinach, you might rely on the leafy green to power your TV set.—E. Sohn

Power Words

bacterium     (pl. bacteria) A single-celled organism. These dwell nearly everywhere on Earth, from the bottom of the sea to inside of plants and animals.

biology     The study of living things. The scientists who study them are known as biologists.

cell     The smallest structural and functional unit of an organism. Typically too small to see with the unaided eye, it consists of a watery fluid surrounded by a membrane or wall. Depending on their size, animals are made of anywhere from thousands to trillions of cells. Most organisms, such as yeasts, molds, bacteria and some algae, are composed of only one cell.

cell membrane     A structure that separates the inside of a cell from the outside of it. Some particles are permitted to pass through the membrane.

electric current     A flow of electric charge — electricity — usually from the movement of negatively charged particles, called electrons.

electricity     A flow of charge, usually from the movement of negatively charged particles, called electrons.

electrode     A device that conducts electricity and is used to make contact with non-metal part of an electrical circuit, or that contacts something through which an electrical signal moves. (in electronics) Part of a semiconductor device (such as a transistor) that either releases or collects electrons or holes, or that can control their movement.

electron     A negatively charged particle, usually found orbiting the outer regions of an atom; also, the carrier of electricity within solids.

membrane     A barrier which blocks the passage (or flow through) of some materials depending on their size or other features. Membranes are an integral part of filtration systems. Many serve that same function as the outer covering of cells or organs of a body.

muscle     A type of tissue used to produce movement by contracting its cells, known as muscle fibers. Muscle is rich in protein, which is why predatory species seek prey containing lots of this tissue.

protein     A compound made from one or more long chains of amino acids. Proteins are an essential part of all living organisms. They form the basis of living cells, muscle and tissues; they also do the work inside of cells. Among the better-known, stand-alone proteins are the hemoglobin (in blood) and the antibodies (also in blood) that attempt to fight infections. Medicines frequently work by latching onto proteins.

semiconductor     A material that sometimes conducts electricity. Semiconductors are important parts of computer chips and certain new electronic technologies, such as light-emitting diodes.

silicon     A nonmetal, semiconducting element used in making electronic circuits. Pure silicon exists in a shiny, dark-gray crystalline form and as a shapeless powder.

solar cell     A device that converts solar energy to electricity.

technology     The application of scientific knowledge for practical purposes, especially in industry — or the devices, processes and systems that result from those efforts.