We have collected some questions and answers that we believe are interesting and relevant to better understand the conditions of transparent photovoltaic (TPV) solar cells, how it compares to other types of solar cells and what advantages it might offer in different applications.

How do your solar cells differ from regular power generating solar cells?

There are many different kinds of solar cells on the market – silicon cells are the most well-known, but there are also organic solar cells, thin-film solar cells (e.g CIGS, CdTe), perovskite solar cells etc.

Yet, our technology differs from all other solar cell technologies in a fundamental way.

The core of our technology – the process for how light is converted to electricity – is different. In other technologies, the mechanism is based on that when a photon is absorbed by the active material, a certain amount of energy is used up to excite an electron from an electronic level to an empty level, and that electron becomes one of the electrons in the electricity current that the cell generates. For a given material, a specific amount of energy is needed to excite (“kick out”) an electron. If the photon has less energy than needed, no electron will be excited by it. If the photon has excess energy compared to what is needed, the excess will be wasted as heat.

Our solar cells build on a mechanism of plasmonic electron resonance. Instead of each photon exciting one specific electron, each photon contributes to the collective excitation of electrons in the material, that produce the current. A result of this different mechanism, is that for a high-energy photon, all of the energy can be converted to electricity – nothing is wasted. There is a limit for how little energy a photon must have for conversion to occur (to produce a cell voltage), but it is much lower than what is typical for other solar cells.

The use of plasmonic electronic resonance from energy conversion enables us to have a much more efficient process since more energy can be converted from the same amount of photons. This means we need to capture much less light to produce the same amount of electricity than an organic solar cell.

*Note: There are also a type of cells called “plasmonic-enhanced solar cells”, that should not be confused with our technology. These are regular solar cells that use plasmonic nanoparticles to scatter light before it is absorbed by the active material. Our cells are direct plasmonic solar cells, where the energy conversion happens directly on the plasmonic nanoparticles.

What is the difference between organic solar cells and Peafowls' technology?

Organic solar cells share some features with our technology when it comes to cell structure and production methods, since we have built on their development of printing manufacturing – read more here. However, the core of the technology is fundamentally different – we use plasmonic nanoparticles to absorb light, which is a process of electron resonance, while organic solar cells use conventional electron excitation processes. The use of plasmonic electron resonance from energy conversion enables us to have a much more efficient process, meaning we need to capture much less light to produce the same amount of electricity than an organic solar cell.

This is the reason why our cells can be clear and colorless, while organic solar cells typically have a dark tinted color (though they are often semi-transparent).

What does it mean that your solar cells are invisible/transparent?

It can seem counter-intuitive that solar cells can be transparent, since transparency is a property of materials that do not capture light while the idea of a solar cell is to capture light and convert it to electricity. The key to transparent solar cells is to design them so that they capture so little light that it is not noticeable.

There are different techniques to achieve this; some work by capturing light of wavelengths outside the visible spectrum (infrared or ultraviolet light), others design the cell as a thin mesh of lines that appear transparent from a distance.

The Peafowl Solar cell is designed to capture small amounts of light in the visible spectrum using plasmonic nanoparticles. The amount of light captured is less than 5% of the incoming light. This can be compared to a normal window that blocks around 50% of the incoming light. The loss of 5% is not detectable by the human eye, and there is no visible coloring, structure or haze on the cell.

What does 90% transparency look like?

The short answer is that 90% transparency looks like “perfect” transparency. A normal window glass, which most of us perceive as fully transparent, is actually only about 50% transparent – and not because higher transparency is difficult to achieve, but because it is desirable to block out some of the incoming light to prevent buildings from overheating when the sun is shining.

When we talk about transparent or “invisible” design, there are a few different concepts to keep track of. Firstly, there is transparency that is described with a percentage: this is the fraction of light that passes through the surface. So, 90% transparency means 90% of the light passes through. Secondly, there is the matter of color. A surface can have a very high transparency, while still having a visible tint or color shade. This is why we emphasize not only transparency, but colorlessness – because a colorless appearance is as important as transparency to achieve an “invisible” design. Finally, there is also the concept of haze. If a surface is transparent and colorless, but is hazy, this means that when you look through it the image becomes distorted and grainy or unclear. Thanks to the ultra-thin design of the plasmonic layer, there is no visible haze in our cells.

However, there is also need to distinguish between the properties of the cell itself and the materials that surround it (“substrates”). Typically, our cells will be printed on a transparent plastic or glass material – there are many options to choose from depending on what properties are desired for the specific application. If the cell is printed on a material that has a lower transparency, tinted color or hazy surface, these properties will of course be there when you consider the properties of the entire device. If you desire a high transparency, colorless design without haze, the selection of these substrates is the most important issue.

Which are the most suitable applications for your solar cells given the power generated?

We are currently testing our technology for two types of applications: indoor sensor devices and dynamic windows. Indoor sensors are used to monitor and optimize the indoor environment of buildings – this is often referred to as “smart buildings”, and is part of the concept called Internet of Things. Buildings that are optimized in this way can be considerably more energy-efficient than buildings with conventional energy management and the technology also enables the tenants to utilize the space more efficiently.

Dynamic windows is an advanced window technology that can adjust the opacity of a window to allow more or less light to pass trough, thereby regulating the energy flow between outdoors and indoors and reducing the need for heating and cooling of the building. Dynamic windows are also used to flexibly change windows panels into multiple purposes indoors for privacy or ambience like walls, dividers or monitors.

A third type of application that we have identified as promising is low-power displays, like e-paper.

Do your cells work indoors?

Yes! Some transparent technologies that are depending on ultraviolet or infrared light need sunlight, but since we capture light in the visible spectrum, this works well with the light sources that are used indoors. Read more here.

What is the efficiency of your cells?

Efficiency of solar cells is generally measured by dividing the electrical energy that is produced by the light energy that falls on the surface. For example, if 100 Watts of light energy falls on a solar cell, and it generates an output of 10 Watts of electrical energy, this cell would be said to have a 10% efficiency.

For transparent solar cells, this becomes a little more complicated, since a lot of the light simply passes through the surface. Say that we have a cell of 50% transparency, and it is exposed to light of 100 Watts. If this cell produces an output of 10 Watts of electrical energy, this would by the conventional definition still count as a 10% efficiency – but it could also be seen as a 20% efficiency of conversion of the light that was intercepted. Only 50W out of the 100W got intercepted by the cell, and if out of these 10W were converted to electricity, this implies a “conversion efficiency” twice that of the opaque cell in the first example.

Since our cells are over 90% transparent, this distinction is important to point out. If we would calculate efficiency the conventional way, we get extremely low values – a few percent, at the very best. This is because most of the light simply passes through the cell.

If we, on the other hand, try to calculate the “conversion efficiency” by comparing the electricity production to the light that is intercepted by the cell, we run into more practical issues. So little light is intercepted by the cell that the amount is difficult to measure accurately, which results in efficiency estimates that are both very high and rather unreliable. Statements about record-breaking conversion efficiencies would furthermore be misleading, since they could easily be understood as that we could produce massive amounts of power, which is not the case.

For practical purposes, the power production is more relevant than efficiency. To power a device, you do not need a certain level of efficiency – what you need is an appropriate combination of voltage and current.

How much do the cells cost?

The cost of a cell will depend on the application and the customer demands – sizes, volumes, durability. A core consideration is what substrate material is needed. If the cell is to be printed on high-quality glass it will be more expensive than if a plastic material can be used.

If you have a specific application in mind and wonder if the Peafowl solar cell could be a feasible solution, please reach out to us with your requirements!

I want to to try it, how do I know if it will work for my application?

The Peafowl cell is not available as a standalone power-source. We would typically work together with developers and manufacturers of low-power devices to develop new, self-powered devices where our cell is an integrated power source.

To assess if the Peafowl cell could be a good solution for a specific application, there are a couple of criteria you can go by:

  • Is there a smooth surface that is exposed to light, where the cell could be mounted?
    Our cell does not need sunlight, or outdoor light, but there needs to be some light available, and there needs to be a smooth surface to print it on.

  • Does the design of the device matter?
    If design is unimportant – as it will be, for example, for many outdoor, industrial or agricultural applications – it is likely that conventional solar cells can do the job at a lower cost. Our advantage is primarily for applications where discrete or appealing design is critical.

  • How much power is needed?
    The power production of a cell is depending on a number of factors – most notably the desired level of transparency, and expected light and surface availability. A rough estimate, however, is that the Peafowl solar cell could be considered as a power source for devices that would otherwise be powered by small batteries for an extended period of time. Mobile phones and laptops are, for example, out of the scope of what our cells could power, for the time being.

If you have a specific application in mind and wonder if the Peafowl solar cell could be a feasible solution, please reach out to us with your requirements!

Can I do a student project/my thesis with you?

We really appreciate the interest we get from ambitious and creative students, but generally we do not have the resources to supervise projects or give interviews for students. There can, however, be exceptions to this if you have very specific skills and training that applies to our technology. If you want to reach out with a request to do a student project with us, please email us with a description of what you would like to do as well as details of your time plan and who your academic supervisor would be. We do not initiate collaborations with students if they do not yet have an academic supervisor connected to the project.

Have another question?

Please, let us know by sending us a message!