Exeger ($130M for flexible solar cells)

Exeger is a Swedish company that specializes in developing and producing customizable solar cells that can convert all forms of light into electrical energy. The company aims to provide world-changing technologies to improve everyday life. Exeger has received significant funding to ramp up production of its flexible solar cells for self-powered gadgets. The company has several products under development, including headphones for JBL.

Challenges: solar power

The use of solar cells to power consumer electronics is nothing new. Today, there are numerous such products available on the market, including solar-powered calculators. The majority utilize semiconductor thin-film solar cells, such as amorphous silicon photovoltaics (PV).

It is well known that mesoscopic dye-sensitized solar cells (DSCs) perform well in ambient light. DSCs are the best alternative to wired and battery-powered energy sources, because they are capable of maintaining a high photovoltage under diffuse light conditions.

DSCs were born in the Laboratory of Photonics and Interfaces directed by Professor Michael Graetzel of EPFL in the late 1980s. The team first introduced a mesoporous TiO₂ colloidal film in the DSC to increase by thousands of times the loading of dye molecules on the surface of TiO₂ films. The mesoscopic DSC significantly improves the ability to harvest light, with a power conversion efficiency over 7%. This is a disruptive innovation. In 1991, their findings were published in the journal Nature.

The author of the book from Professor Graetzel’s lab provides a comprehensive look at this promising technology.

Conventional dye-sensitized solar cells.

Small area laboratory DSC fabrication is simple. Using screen printing technology, mesoporous electrodes are created. In order to establish an electronic connection between the nanoparticles and the printed electrodes, the electrodes were typically sintered at 500 degrees Celsius. In a dye bath, the mesoporous TiO₂ electrode is stained. The TiO₂ electrode and counter catalytic electrode are assembled and sealed with adhesive polymer foil. There is an electrolyte in between. The small area laboratory DSCs have achieved stability under dual light soaking and heat stress aging conditions, and their power conversion efficiency can exceed 10%.

A conventional flexible dye-sensitized solar cell typically employs two conductive films as charge collectors. Both conductive charge collectors may be transparent conductive oxide coated polymer foils, or one may be metal foil and the other transparent conductive oxide (such as indium tin oxide) coated polymer foil. Generally, the transparent conductive oxide coated polymer foils are manufactured using vacuum coating technology. The cost is high. Thereby, the cost of flexible DSCs may be higher than amorphous silicon photovoltaics.

Exeger Technology

Exeger has created Powerfoyle, an emerging flexible and lightweight PV technology based on DSCs. It is the result of more than ten years of Exeger research and development.

Exeger powerfoyle technology

Powerfoyle employs a piece of inexpensive glass fabric (tens of microns thick) coated on both sides with conducting porous layers that serve as charge collectors. On the surface of the first conducting porous layer is coated with mesoporous TiO₂ film of several microns in thickness. An insulating porous layer is provided at the bottom to prevent the electronic contact between the first conducting porous layer and the platinum-loaded nanoparticles embedded in the glass fabric. The platinum-loaded nanoparticles that form an interconnected network within the fabric are connected to the second conducting porous layer. After high temperature sintering, room temperature sensitization, and electrolyte deposition, the fabric and electrolyte are laminated with polymer foils.

Therefore, in Powerfoyle, the light utilization is the most effective, as no light is lost due to the transparent conductive oxide layer’s light absorption, as in conventional DSCs. The photo-excited dye molecules inject electrons into the TiO₂ film, which transport the electrons to the first conducting porous layer. The oxidized dye molecules are regenerated by iodide ions in the electrolyte, yielding triiodide ions. The iodide/triiodide redox couple diffuses through the insulating porous layer. The electron flow reaches the second conducting porous layer through an external power load, and the electrons are distributed on the surface of the platinum-loaded nanoparticles to reduce triiodide ions to iodide. This smart solution revolutionizes flexible dye-sensitized solar cell technology.

Thanks to the highly conducting fabric as charge collectors, Powerfoyle is able to maintain efficient power conversion efficiency despite the expansion of the photosensitive area. The large-area Powerfoyle can therefore adopt a single-cell design, without internal sub-cells, embedded silver wires, and internal sealants, to avoid the stability problems caused by sealants and shadow.

Powerfoyle’s power conversion efficiency and stability under standard testing conditions are not disclosed. However, stable laboratory dye-sensitized solar cells have a power conversion efficiency of 5 to 10% in direct and diffuse sunlight. Under indoor lighting, their performance surpasees that of amorphous silicon PV. According to prior research on DSCs, Powerfoyle is capable of achieving good performance and stability. Future advancements in photosensitizers, electrolytes, and interface engineering will reduce the charge recombination in Powerfoyle, thereby enhancing its performance.

Exeger Products

Products with elegant designs and solar energy solutions can always win the hearts of consumers. Exeger and JBL collaborated to release Powerfoyle-powered headphones. JBL uses Indiegogo to crowdsource interest for this product. JBL hopes to obtain user feedback on this technology through close collaboration with potential users so that it can meet the needs of users. Exeger is collaborating with others to integrate their solar cell technology into other products, such as solar bags.

Exeger Funding

Exeger has raised a total of $185.7M in funding over 12 rounds, including a Funding round, a Second Market round, seven Venture-Series Unknown rounds, a Debt Financing round, and two Series B rounds. Their latest funding was raised on Feb 23, 2023 from a Series B round.