Opportunity knocks for third generation PV

It quickens the pulse of many within the solar industry to see artists’ visions of the future in which PV is pervasive – on rooftops, integrated into buildings and vehicles, and a part of the very fabric of our cities and urban environments.
It is commonly acknowledged by many in the field that standard PV modules, which still account for the vast majority of the global PV industry, will not be able to meet the needs of ubiquitous PV. This is where third generation PV applications including organic PV (OPV) technology comes into its own.
However, it has been difficult in recent years for OPV to convince the solar market of its potential upside, when prices for higher efficiency conventional PV modules have been falling so fast. But this, argues Belectric OPV CEO Ralph Pätzold, does not take into account the key performance indicators (KPIs) that uniquely apply to OPV.
“What are the KPIs of organic printed PV? Low light performance, shadowing performance, low temperature coefficient – not under STCs – design transparency, color, and freedom of shape,” says Pätzold.
When assessed according to these criteria, OPV has a differentiated place in the market.
Belectric OPV is currently working with the designers of the German pavilion for this year’s World’s Fair, to be held between May and October in Milan, Italy. The fair’s theme this year is “Feeding the Planet, Energy for Life” and Belectric OPV’s modules will be integrated into solar trees that will “connect the interior and exterior space” of the German Pavilion, in the words of Belectric OPV’s Hermann Issa, who is the Project Manager for the application of OPV in the pavilion. Carl Stahl GmbH, U.I. Lapp GmbH, Merck KGaA and the German Federal Ministry for Education and Research are also contributing to the OPV component of the World’s Fair pavilion.
Beyond this striking and visionary application of OPV technology, Belectric’s Pätzold additionally argues that building regulations and rating systems in the EU (EnEf) and the U.S. (LEED) will be drivers of OPV deployment. With insulation and energy efficiency measures only going so far towards building construction and operation achieving low or eventually zero energy consuming structures, Pätzold says that BIPV applications using OPV can now be applied to the overall energy performance of a building.
“Thirty percent of our energy is consumed in buildings,” explains Pätzold. “The new regulations work on a net balance model, so to a certain extent you can substitute passive insulation with actively produced PV electricity.” Looking towards market size, he points to the 450 million m² of new building surfacexAdvertisementarea per year that could potentially be addressed by OPV in Germany alone.

Products and cost

To address even a part of this emerging market, OPV products need to meet cost, performance and durability requirements. A range of research bodies and companies investing in endeavors are doing just this.
One such project is the Rotrot project launched in 2011, which involved seven participating parties from five different countries. The project’s name stands for ‘roll-to-roll production of organic tandem cells’. Rotrot was funded by the EU.
“Rotrot proposed a complete solution process using significant advances in roll-to-roll (R2R) techniques ending up with an environmentally friendly and safe deposition process,” explains Owen Lozman, Merck’s OPV R&D Manager. “To fulfill this goal, specific advances were made in high performance materials (photoactive polymer, electrodes, high performance interface, barrier adhesive), device architecture design based on tandem structure, development of an ‘R2R all solution process’ using simultaneous multilayer formation.”

Tandem challenges

A tandem structure for the OPV solution targeted by the Rotrot project was chosen for its conversion efficiency boosting qualities. With a tandem organic PV stack, a larger part of the solar spectrum can be harnessed by the OPV cells. But this does not come without its challenges.
“The production becomes more complicated since the structure requires multiple layers to be deposited on top of each other,” says Merck’s Lozman. Through tapping “state of the art materials and delicate processes,” Lozman says that in early 2014 the Rotrot project was able to achieve its goal.
In a joint workshop hosted at the Technical University of Denmark, Rotrot collaborators were able to achieve the production of a 14 layer tandem ITO-free OPV structure that could be produced under atmospheric pressure and low temperature.
A roll-to-roll process was employed in the Rotrot project, as Lozman says printing technologies on to flexible substrates fulfilled “low cost and easy manufacturing” criteria.

Low cost is key

As with all PV technologies, cost remains king. The Rotrot team produced a range of material and production scenarios through which production costs could be analyzed.
The findings were published in the Energy & Environment journal in July 2014, under the title: “Cost analysis of roll-to-roll fabricated ITO free single and tandem organic solar modules based on data from manufacture.” A cost target of €0.05/W ($0.05) was set and various configurations of the tandem layer, swapping in and out high cost active layers, and a range of production sizes, such as pilot-scale, 100 MW and even up to 100 GW, were modeled. “The challenges faced on the path to commercialization are now much more tangible and clearly defined than they were at the start of the project,” says Merck’s Lozman.

Early applications

Looking towards early applications of the technology, Lozman identifies a range of potential applications. These include opportunities in supplying the rapidly growing but early stage Internet of Things applications, such as in powering indoor sensors and relays facilitated by the relatively high efficiency in indoor application; and application in wearable devices due to the variety of colors that can be achieved.
Color and semi-transparency also offer commercial applications in the longer term. The Rotrot team envisages inte
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gration into smart buildings and mobility devices, from trains to automobiles.
“We can start to make beautiful and functional energy harvesting surfaces out of many structural materials such as glass and building facades,” adds Lozman.
The words “beautiful and functional” are almost as key as cost when it comes to BIPV applications. As Belectric OPV’s Pätzold says, the way a BIPV component is defined is completely different to standard PV modules. “You need to convince the building owner and the architect that you are not delivering a PV product but a building construction product,” says Pätzold. “The architect wants to have design, not black, not rectangular, it needs to be something cool.” Something “cool” is also something that OPV pioneer Michael Grätzel has been working towards throughout his long career in the field, although perhaps unwittingly. “The market asks for grey and blue colors,” says Grätzel, “especially in the MENA countries.” Grätzel has long been working on the commercialization of dye-sensitized PV, now incorporating the fast-growing field of pervoskites.
Swiss company g2e (glass2energy) is currently producing and supplying architects with dye-sensitized glass under license, and some of the applications clearly qualify as being both beautiful and cool. The glass facade of the SwissTech convention center on the EPFL Campus is an excellent example, with Grätzel himself reporting that people come from as far away as South America to take in the innovative and striking use of PV material.
pv magazine understands that the conversion efficiency for the glass in the SwissTech building is in the low single digits range, but it clearly demonstrates that design may triumph over function when it comes to third generation PV applications. Grätzel says that indoor spaces will also soon be “overtaken by PV,” something that Merck’s Lozman too indicates. With markets clearly emerging, a low-cost tandem structure may have the flexibility of applications and aesthetic qualities required to open the promise of ubiquitous OPV.
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