PCBM Full Form – All Important Facts You Need to Know about This Outstanding Fullerene Derivative

PCBM full form is [6,6]-phenyl-C₆₁-butyric acid methyl ester. If you are interested in nanotechnology and you are also familiar with the term clean energy, this is probably not the first time you have come across this fullerene derivative.

It certainly deserves your attention. Why? There are actually plenty of reasons. One of the most threatening is the global warming. It is more than clear that we need a clean renewable energy source that does not produce carbon dioxide and other greenhouse gases. The good news is that there are such energy sources.

There is no doubt that the future is in obtaining the energy directly from the sunlight by using photovoltaic technology. Specifically organic photovoltaic cells (OPVs) could be the right solution.

Would you like to know why that is? Are you curious how does it work? Are you searching for more elaborate and complex information?

In that case this article is really worth reading. It will introduce all basic terms you need to be familiar with in order to gain a full understanding of the tremendous potential of PCBM.

“I’d put my money on the sun and solar energy, what a source of power. I hope we don’t have to wait until oil and coal run out before we tackle that.”

Thomas Edison, 1931

PCBM Full Form – Very Promising Organic Solar Cell Material

First of all you should know that the polymer solar cells (PSCs) are in the center of attention of the photovoltaic community for the last two decades.

As it was mentioned above the world is facing a real energy crisis. We are running out of fossil fuels. That is just one problem we are going to face in the very near future. We do not need to only produce the electricity somehow. We urgently need to produce it in a clean and renewable way.

Organic photovoltaic cells (OPVs) are one of the possible solutions. When compared to conventional semiconductors they have several very promising advantages.

Particularly P3HT PCBM [poly (3-hexylthiophene) (P3HT) and 1-(3-methoxycarbonyl) propyl-1-phenyl [6, 6] C 61 (PCBM)] is the most researched polymer blend in the world. It is because it increases the energy efficiency.

The PCBM Absorption Spectrum Plays an Important Role in the Solar Cells Efficiency

The main purpose of solar cells or photovoltaic cells is to transform the sun’s radiation into electricity which is done through photovoltaic effect.

But there is a catch. The organic polymers have limited absorption spectrum and poor charge mobility. What does it mean? It means that their efficiency is quite low.

Nevertheless fullerene derivatives are very effective electron acceptors. This basically means that the combination of fullerene derivative and narrow-band donor could be a possible solution. This way it could be produced efficient organic cells.

P3HT PCBM is a great example of such an approach as it is the most efficient organic cell.

That is just a brief introduction into this fascinating topic. Let’s dig deeper so that you can get to know more detailed information about PCBM and organic solar cells.

What Is PCBM Fullerene?

It was already stated above that PCBM is a chemical formula for [6,6]-phenyl-C₆₁-butyric acid methyl ester. So it is a fullerene derivative. To be absolutely precise, it is a derivative of C₆₀ fullerene.

What Is C₆₀?

The formula C₆₀ also known as Buckminsterfullerene or Buckyball set the base for the whole new field of nanotechnology.

It was discovered by a trio of scientists Richard Smalley, Harry Kroto and Robert Curl Jr. at Rice University in Texas in 1985.

Buckminsterfullerene got its name after Richard Buckminster Fuller. He was American architect, futurists, designer and author, who designed the famous geodesic domes. The buckyballs resemble mathematically and structurally the structure of Fuller’s geodesic dome.

Buckyball was the first fullerene discovered. It is perfectly symmetrical molecule with absolutely amazing set of properties that suggest limitless number of possible applications.

This revolutionary discovery was later (in 1996) recognized by the Royal Swedish Academy of Sciences. The three scientists were awarded the Nobel Prize in Chemistry.

And that was just the beginning of an intensive research of fullerenes and their derivatives.

Did You Know?

The first microscopic amounts of C₆₀ were not produced at the Rice University by the team around Smalley, Kroto and Curl. Although they had been trying for two years they did not succeeded.

It was the scientists Donald Huffman and Wolfgang Kratschmer who did it. The result of their hard work was published in the journal Nature in 1990. The scientific world was provided with the evidence of its existence. Soon after that the fullerenes experienced a boom. Everybody wanted to research this peculiar molecule. Fullerenes were in high demand, although the scientists had to pay over 1000 $ for 1 g of C₆₀.

Fortunately that time is over. Today you can buy fullerenes for much affordable prices thanks to the advanced technology and progress in the processes of synthesis.

The First Synthesis of PCBM 60

[6,6]-phenyl-C₆₁-butyric acid methyl ester was synthesized for the first time in 1995, only ten years after the first fullerene was discovered. The aim was to produce soluble fullerene derivatives so that they could be used for applications in physics and medicine.

First PCBM was developed by a group of scientists around Prof. Wudl at the University of California in Santa Barbara.

Who is Prof. Fred Wudl?

Prof. Wudl is famous for his research of organic conductors and superconductors. He discovered the electronic conductivity of the predecessor to the first organic metal and superconductor. He is also behind the discovery of the first transparent organic conductor and the first self-doped polymers.

Right now he is researching the optical and electro-optical properties of conjugated polymers. He is also interested in the design and production of self-healing and self-melding materials and also in the organic chemistry of fullerenes.

More Important Facts about [6,6]-phenyl-C₆₁-butyric Acid Methyl Ester

• It is an electron acceptor material. This means that it can accept electrons that are transferred to it from another compound. The electron accepting power of an acceptor molecule is measured by its electron affinity (E_ea). The electron affinity is in fact the energy that is released when filling the lowest unoccupied molecular orbital (LUMO). We will get back to it later in separate chapters, where you can find more elaborate information.
• Thanks to its unique structure and properties it is used in plastic solar cells and electronics. That is in conjunction with electron donors polymers.
• The example of such a conjunction is P3HT PCBM, which is also the most efficient solar cell.
• If compared with other fullerenes, PCBM is a more practical option for an electron acceptor, because it is soluble in chlorobenzene.

PCBM Solubility in Organic Solvents

As you can read above this fullerene derivative can be dissolved in chlorobenzene.

It is soluble in other organic solvents as well, such as:

• chloroform
• toluene
• xylenes

It is insoluble in water.

Does the Use of Aromatic and/or Chlorinated Solvents Have an Impact on the Environment?

The aim is to get higher performances (energy efficiency) of the photovoltaic devices. The thing is that it is still necessary to use aromatic and/or chlorinated solvents in the organic semiconductor ink formulations.

The scientists already substitute the chlorinated solvents by xylene in order to lower the negative impact on the environment. However the use of such aromatic solvents can not be considered environmentally friendly as they still have quite significant impact on it.

But there is an alternative to those solvents. It is the formulation of water-based colloidal inks for organic photovoltaics.

Kietze and Landfester started the research on that matter in 2002. In 2004they produced the first organic photovoltaic device using water-based colloidal inks.

They adapted and optimized the mini-emulsion technique in order to create different kind of colloidal solutions of organic semiconductors. They used:

• Donor polymer: PFB (poly(9,9-dioctylfluorene-co-N,N-bis(4-butylphenyl)-N,N-diphenyl-1,4-phenylenediamine))
• Acceptor polymer: F8BT(poly(9,9-dioctylfluorene-co-benzothiadiazole))

The result was up to 4 % at 380 nm in the external quantum efficiency. The performance was low, but many other scientists continue to develop this idea.

Fortunately we have the unlimited source of clean energy; the Sun. What could be a hard nut to crack is that the scientists have to find low cost and effective way how to utilize it. The challenge is on.

Nevertheless, the nanotechnology is a very fast evolving science. So we might witness a major progress in very near future.

Look below at the timeline of the solar cells development.

From the First Solar Cells to the P3HT PCBM Synthesis

It might surprise you, but the idea of photovoltaic effect was discovered already in the 19^th century. However the first actual solar cell was produced decades later.

The Development of the Solar Cells

1. The Si p-n junction modern solar cell was created in 1954.
2. The first highly effective GaAs heterostructure cell was produced by Zhores Alferov and his team in the Soviet Union in 1970.
3. In 1980 there were made the first thin film cells. It was at the University of Delaware and they reached 10 % efficiency (with Cu2S/SdS).
4. The first dye-sensitized cell was developed in 1991.
5. In 1994 when the scientists used GaInP/GaAs, they reached the efficiency of 30 %.
6. To exceed the barrier of 40 % took twelve more years, they achieved it in 2006.

Nowadays the scientists focus on the carrier collection, the cell stability and also increasing the sunlight concentration.

Moreover, the scientists are interested not only in inorganic chemistry. That is definitely a step in the right direction.

Although it is true that the organic polymers are not as effective as the organic ones, their structure is so unique that it is definitely worth investigating.

PCBM Solar Cells Could Be More Effective and Less Expensive Alternative to Conventional Silicon Solar Cells

The scientists are literally on the quest to find a low cost, renewable and clean energy source. Considering that matter PCBM solar cells might be just it.

To be absolutely clear we speak about P3HT PCBM solar cells as this fullerene derivative proved to be the most effective.

As its formula suggests it consists of two components:

• PCBM - [6,6]-phenyl-C₆₁-butyric acid methyl ester
• P3HT – its full form is poly(3-hexylthiophene). It belongs to the Polythiophene family. This conducting polymer is mainly used in organic electronics. It has regular end-to-end arrangements of the side chains. The photovoltaic effect in P3HT PCBM is possible thanks to the excitation of the π-orbit electron in P3HT.

P3HT PCBM full form is poly (3-hexylthiophene) (P3HT) and 1-(3-methoxycarbonyl) propyl-1-phenyl [6, 6] C 61 (PCBM)

This polymer blend has several amazing advantages over the silicon made solar cells.

• It is more effective (higher energy efficiency).
• It is cheaper to produce.
• It has better physical durability.
• It also has more accurate allocation of resources.
• It is lighter.

However, as amazing as it sounds there are also certain disadvantages that still need to be solved. P3HT PCBM solar cells do not have a long life span. Why is that? It is because P3HT reacts with the water vapor that is present in the air. Such solar cells would have to be changed more often.

The Fossil Fuels Still Run the World

In the present time crystalline Si solar cells are the most dominant photovoltaics in the market (85 %). But they represent only 0.1 % of the total world energy production.

To sum it up, although silicon is a non-toxic material that is present in the Earth’s crust, the large production costs for silicon based technology are very high. The sustainability of such technology is also limited to the availability of the raw material.

That is why it is necessary to develop new materials and device structures. P3HT PCBM is one of the promising candidates that could fulfill such requirements.

“If we use our fuel to get our power, we are living on our capital and exhausting it rapidly. This method is barbarous and wantonly wasteful, and will have to be stopped in the interest of coming generations. The heat of the sun’s rays represents an immense amount of energy vastly in excess of waterpower.”

Nikola Tesla, 1915

The die of fossil fuels was cast the day we started to use them for energy production. Nikola Tesla could foresee that more than 100 years ago. He could also see the huge potential in utilizing the energy from the sun radiation.

In this chapter were summarized the pros and cons of both silicon based and organic solar cells to get a better idea of what obstacles lie on the way to low cost, high efficient and clean energy.

But we are not going to stop just there. Instead we are going to get to the heart of the matter.

The following chapters will focus on electron affinity of PCBM.

Electron Affinity – PCBM HOMO LUMO

As it was already mentioned before the electron affinity refers to the energy released when the lowest unoccupied molecular orbital (LUMO) is filled.

What Is Molecular Orbital?

Molecular orbital (MO) is described as an orbital or wave function of an electron in the molecule.

This function can be used to determine chemical and physical properties. For instance, it can calculate the probability of finding an electron in any specific region.

This term was introduced for the first time by Robert S. Mulliken in 1932. He was American physicist and chemist, who developed the molecular orbital theory.

The orbital is in fact an abbreviation for one electron orbital wave function. It represents the region of space. In this space the function has significant amplitude.

Molecular orbital is usually built by combining atomic orbitals or hybrid orbitals (from each atom of the molecule).

There are three types of molecular orbitals:

• Bonding MOs
• Antibonding MOs
• Nonbonding MOs

HOMO and LUMO Bonding in Molecular Orbitals

HOMO – highest occupied molecular orbital

LUMO – lowest unoccupied molecular orbital

You can also come across the term HOMO-LUMO gap, which represents the difference of their energies.

What Is the Electronic Structure in Organic Semiconductors?

You should know that the electronic structure of all organic semiconductors is based on conjugated π-electrons.

Just imagine that a conjugated organic semiconductor is formed by an alternation of single and double bonds (carbon-carbon).

• Single bonds – also known as σ bonds. They are associated with localized electrons.
• Double bonds – they consists of σ bonds and π bonds.

It is important to mention that the π electrons are much more mobile than the σ electrons.

What does it mean in practice?

It means that the π electrons can literally jump from site to site between carbon atoms. This is possible thanks to the mutual overlap of π orbitals.

The result is that the wave functions delocalize over the conjugated backbone.

And we are getting to the point. The π bands are either empty (LUMO) or they are filled with electrons (HOMO).

To sum it up in organic materials such as PCBM or P3HT PCBM the energy equals the difference between the energy of the lowest occupied molecular orbital and the energy of the highest occupied molecular orbital. The extra energy is wasted (as heat).

Important Data – P3HT and PCBM LUMO and HOMO

What is Bis-PCBM?

Bis refers to bis-adduct, which is in fact a product of two simultaneous addition reactions on one molecule.

Why you should know more about it? Recently scientists have become very interested in fullerene bis-adducts. What attracts their attention is the high-lying LUMO level.

This means that bis- PCBM can increase the efficiency of the solar cells.

For More Detailed Information about Particular Products Check PCBM MSDS

If you want to make sure about certain chemical or physical properties of PCBM or any other fullerene material, you can look into its Material Safety Data Sheet (MSDS).

Material Safety Data Sheet is required under the OSHA Hazard Communication Standard.

Good Advice

The MSDS provides detailed information about a hazardous chemical (product). It is prepared by the producer or importer. It should be an accurate list of all chemical and physical properties, emphasizing all the possible risks. However, you should not rely on it completely as many MSDS contain inaccurate information. Be always cautious.

The Summary

PCBM represents a cleaner, cheaper and renewable alternative to fossil fuels.

This article stressed out that the energy crisis is a real problem that needs to be solved as soon as possible.

Fortunately there are many ongoing researches whose aim is to find an effective and inexpensive way to utilize solar energy.

Thanks to this article you know the difference between silicon and organic solar cells.

You are aware of their advantages and disadvantages.

It was also mentioned that one of the latest focus is two substitute the aromatic solvents by water based colloidal solvents in order to improve the impact on the environment.

Last but not least you got to know more about molecular orbitals.

This article has only scratched the surface of the development of effective organic solar cells.

Hopefully it encourages you to find out more interesting facts about PCBM fullerene derivatives.

Do you agree that the solar energy is the best solution of the fossil fuels crisis?

Do you think that it is not a matter of research, but also about politics?

Are fullerenes the right choice materials?

Please share your opinion and theories with us.