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Photovoltaic solar cells: The future's bright

Feb. 6, 2018

In 1839, Edmond Becquerel was tinkering in his father’s lab. He had recently become interested in studying the interaction of light with various materials, and so he decided to take some platinum electrodes and place them in an acidified silver chloride solution. The young Frenchman noted that nothing much happened to this experimental set-up in the dark; however when he illuminated the solution, a combination of these materials and light caused a current to be generated within the electrodes. What Becquerel had just stumbled upon was the world’s first photovoltaic device. But what are photovoltaics, and how are they used today?

What are photovoltaics?

An explanation for how photovoltaics worked eluded scientists for many years. It wasn’t until 1905 that a young Albert Einstein proposed a radical new theory: in a paper on the ‘photoelectric effect’ he stated that light, rather than a beam, is more accurately described as discrete, quantized ‘packets’ of energy called photons. These photons interact with electrons in solid material to produce electric effects. This revolutionary idea was further reinforced with subsequent experiments, and won Einstein the Nobel Prize in Physics 16 years later. Since the discovery and further explanations of the photoelectric effect, scientists have been experimenting to produce yet more complex and innovative photovoltaic devices.

Photovoltaic devices are typically made from semiconducting materials that are specially ‘doped’ with other elements that have an excess or deficiency of electrons – essentially creating positive and negative electrodes. These positively and negatively doped semiconductors are then sandwiched together as a thin wafer. When light strikes this photovoltaic device, electrons are dislodged by the incoming photons. When electrical conductors are attached to the positive and negative sides, an electrical circuit is formed, and the displaced electrons can flow through the conductors as an electrical current. The current produced is directly proportional to the amount of light that strikes the device.

How are photovoltaics used?

With renewable sources being championed as the solution to our energy needs, the idea that something as ubiquitous as sunlight can be converted into a usable supply of electricity is certainly an enticing one. In the case of modern-day solar panels, these are made up of many photovoltaic devices, called solar cells, which convert sunlight directly into electricity. Since their tentative beginnings, photovoltaics are now the third most popular source of renewable energy, after hydro and wind powers. A major benefit of these solar panels is that they operate at low costs with little environmental impact, and reliably produce electricity with minimal maintenance.

The first generation of commercial solar cells that were developed were all silicon-based. Silicon is an ideal material for photovoltaics as it is an intrinsic semiconductor, is abundant, and can be easily doped. Manufacturing these cells involves high-purity silicon being processed into crystalline wafers about the thickness of a human hair. These crystal varieties can be either ‘monocrystalline’ or ‘polycrystalline’ silicon.

Monocrystalline silicon solar panels are a popular choice in photovoltaics, as they are the most efficient and dependable way to harness electricity from the sun. They are also some of the most durable cells commercially available, as they can last decades with only a slight reduction in efficiency. If the goal is to produce the most amount of electricity in a given area, these are the panels to use. As such, they are a common way to produce renewable energy in urban applications where space is limited.

A second generation of photovoltaics

Invented in the 1970s, a new wave of thin-film solar cells began to be studied as a possible alternative to the earlier models. Common thin-film alternatives include ‘cadmium telluride’ and ‘CIGS’ cells. Instead of growing crystalline wafers, second-generation materials are usually deposited as a very thin layer onto a substrate. The thickness of the film varies, but can be as thin as a strand of human DNA! The substrate might be anything from metal to glass, or even plastic; meaning that for the first time flexible and curved solar cells could be constructed for energy generation.

An advantage of the thin-film second-generation solar cells is that they are cheaper to manufacture than crystalline silicon solar cells, but this reduction in cost comes at the price of efficiency. Despite great improvements in design and manufacturing over recent years, most are still less efficient than first generation cells. The highest efficiencies achieved for thin-film solar cells in laboratories is 21 percent, slightly outperforming polycrystalline silicon (which offers conversion efficiencies of approximately 19 percent). Additionally, another drawback for renewable energy applications is that they have brief lifetimes of approximately 20 years – much shorter than silicon equivalents.

The bright future of photovoltaics

Since their discovery over 150 years ago, our fascination with photovoltaics shows no signs of slowing down. In fact, applications of photovoltaics have been gaining more momentum recently, and their implementation has grown exponentially over the past ten years. There are many innovative new materials being developed to harness the sun’s energy more effectively. Emerging ‘third-generation’ photovoltaics have exotic names like quantum dot, perovskite, organic, and dye-sensitized solar cells, and are funded heavily because they look likely to achieve the goal of producing high-efficiency solar cells at a low cost. Solar cells currently contribute about two percent of global electricity, but it’s predicted that by 2050 they will be the world’s largest source of electrical power. Meaning that it’s safe to say the future is looking bright for photovoltaics.

Alfa Aesar produces a range of high-purity materials specifically for the photovoltaic industry, including a number of products critical to the solar cell production process.  If you would like to learn more about the products available, or require a specialized compound, then please visit our metals and materials pages, or contact us today.

 


 

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