Millennium Prize-winning ALD technology enables the fabrication of highly efficient solar cells

Doctoral student Jesse Saari fabricates titanium oxide and aluminium oxide thin films for solar energy applications with TUT’s ALD reactor.

Doctoral student Jesse Saari fabricates titanium oxide and aluminium oxide thin films for solar energy applications with TUT’s ALD reactor.

The Technology Academy Finland has awarded the Millennium Technology Prize to Finnish inventor and physicist Tuomo Suntola for developing atomic layer deposition (ALD) into a versatile thin film growth method for nanotechnology. Researchers at Tampere University of Technology (TUT) are using ALD, for example, in the development of highly efficient and flexible solar cell materials.

The biennial Millennium Technology Prize given out by the Technology Academy Finland has been awarded to Finnish physicist Dr. Tuomo Suntola, whose ALD innovation is a nanoscale technology in use all over the world. Dr. Suntola was appointed as Adjunct Professor at Tampere University of Technology in 1976.

ALD is an extremely precise and controllable technique for depositing thin films onto a substrate. It is being used in a broad range of everyday applications, such as CD players, fibre-optic communication systems, barcode readers, material processing equipment, radars, sensors, mobile technologies – and even in silver jewellery to prevent them from tarnishing.

“ALD-grown thin films are especially useful in the manufacture of micro- and optoelectronic components that are becoming increasingly smaller and more densely packed. For the memory circuits of computers to work reliably, they must be fabricated to meet the requirements of the ever-shrinking dimensionality of the components. Similar conformal coatings for topographically enhanced substrates are also needed in optical components, sensors and solar cells,” describes Professor Mika Valden from the Laboratory of Photonics at TUT.

ALD is one the technologies that Valden and his surface science research group are utilising in their work.

“ALD-grown thin films have been used at TUT since 2014, when the ALD reactor manufactured by the Finnish company Picosun Oy was deployed in the Surface Science Laboratory. The reactor was acquired as a part of a Finnish infrastructure project with financial support provided by the Academy of Finland and TUT,” says Valden.


The international Millennium Technology Prize was awarded in Helsinki on 22 May 2018. The Millennium Technology Prize is a Finnish €1 million award presented every second year in honour of a pioneering technological innovation that improves people’s quality of life and promotes sustainable development. The winning innovations must have extensive positive social impacts, be commercially viable and promote the welfare of humanity. Read TAF's media release and watch a video of the winner


The ALD technique is based on a sequential, layer-by-layer deposition of mutually reactive compounds onto a substrate.

“What makes the method so special is its controllability. The surface-controlled and self-limiting nature of ALD means that the coating is created one thin film layer at a time, resulting in a uniform coating structure that perfectly conforms to complex 3D surfaces,” says Valden.

New inroads into solar cell development

Valden’s group fabricates ALD-grown thin films for different research groups at TUT, but the most active users are found in the Laboratory of Chemistry and Bioengineering and especially the Laboratory of Photonics at the Faculty of Natural Sciences.

“The material properties of ALD-grown thin films are unique. There is no other method available for fabricating similar thin film structures. Besides, we can adjust the growth conditions in the ALD reactor to create different polymorphic structures of the same thin film and thereby tailor the properties to suit each individual application,” says Valden.

“ALD has allowed us to reach an unprecedented degree of control over the interdependencies between the properties, structure and production of nanomaterials, which has generated widespread interest not only among research groups at TUT but also companies specialising in optics or materials science.”

A whole new avenue of research involving ALD-grown thin films is the manufacture of novel solar cell materials at TUT. Instead of generating electricity, the solar cells utilize the Sun’s energy to convert water and carbon dioxide into hydrogen/carbohydrates and oxygen imitating the natural process of photosynthesis.

“The energy captured from sunlight can be stored in the chemical bonds of hydrogen/carbohydrates.
To optimise the functionality of these solar cells, their surface is decorated by an ALD coating,” says Valden.

Text: Sanna Kähkönen
Photo: Valtteri Pönkkä