Solar photovoltaic cells, often simply referred to as solar cells, have revolutionised the way we harness energy from the sun. These ingenious devices convert sunlight directly into electricity, providing a renewable and environmentally friendly source of power. But how do they actually work? The process is both fascinating and complex, involving the principles of physics, chemistry and materials science.
At the most basic level, a solar cell operates by absorbing light and converting it into electricity. This is achieved through the properties of certain materials which, when exposed to light, can absorb photons and release electrons. These freed electrons are then captured and channelled into an electrical circuit, creating a flow of electricity.
The key component in this process is a type of material known as a semiconductor. Semiconductors have unique properties that allow them to behave in this way, sitting somewhere between conductors (which allow electricity to flow easily) and insulators (which do not).
Semiconductors are typically made from silicon, a plentiful element found in sand. Silicon atoms bond together to form a tightly packed lattice structure. Each silicon atom shares its four outermost electrons with its neighbours, creating a stable structure with no free electrons to conduct electricity.
However, when a small amount of other elements are added to the silicon lattice, a process known as doping, the balance is tipped. Depending on the type of dopant used, either extra free electrons are added, or empty spaces known as ‘holes’ are created. This results in a material that can conduct electricity under the right conditions.
The magic of solar cells lies in a phenomenon known as the photovoltaic effect. This was first discovered by French physicist Edmond Becquerel in 1839, and it is this effect that allows solar cells to convert sunlight into electricity.
When light hits the semiconductor material in a solar cell, it can give enough energy to an electron to free it from its bond. This creates a free electron and a hole. If these are separated before they can recombine, an electric current can be created.
To separate the electrons and holes, a solar cell is made up of two types of semiconductor material: n-type, which has extra electrons, and p-type, which has extra holes. When these two materials are placed together, they form a junction. At this junction, some of the extra electrons from the n-type material fill the holes in the p-type material, creating an electric field.
This electric field acts like a one-way street, allowing electrons to move from the p-type material to the n-type material, but not the other way around. When light creates new electron-hole pairs, the electric field pushes the electrons towards the n-type material, creating a flow of electricity.
A single solar cell produces only a small amount of electricity. To generate a useful amount of power, many cells are connected together to form a solar panel. These panels are then connected together to form a solar array, which can be used to power homes, businesses, and even spacecraft.
Each cell in a solar panel is connected in series, meaning that the electric current must pass through each cell in turn. This allows the voltage to be increased, while the current remains the same. The result is a higher power output.
There are many factors that can affect the efficiency of a solar cell, from the quality of the semiconductor material, to the angle and intensity of the sunlight. By carefully designing and positioning solar panels, it is possible to maximise their output and make the most of the available sunlight.
For example, solar panels are often mounted on adjustable frames, allowing them to be tilted towards the sun as it moves across the sky. They can also be coated with anti-reflective materials, to ensure that as much light as possible is absorbed rather than reflected away.
While the basic principles of solar cells have remained the same for many years, there is still much research being done to improve their efficiency and reduce their cost. New materials and technologies are being developed, such as thin-film solar cells and multi-junction cells, which promise to deliver even higher efficiencies and make solar power even more accessible.
As our understanding of the science behind solar cells continues to grow, so too does our ability to harness the sun’s energy. The future of solar photovoltaic cells is bright, and they will undoubtedly play a key role in our transition to a sustainable, low-carbon future.
