1. What means „organic“ in „organic photovoltaic“?

The word "organic" is derived from the choice of materials for the active layer. The active layer consists of a polymer and a fullerene (both organic) sandwiched between two electrodes (mostly inorganic). For more details concerning materials see FAQ 7.

2. How do OPVs generate electricity?

Organic photovoltaic (OPV) cells convert electromagnetic energy (sun light) into electricity by the photovoltaic effect. Assemblies of cells are used to make solar modules or photovoltaic arrays. The way OPV cells convert electromagnetic energy is described below:

The photons travel through the contact materials and hit the active layer. At this point, three things may happen for the photons:
  • The photons pass straight through the active layer. This generally happens for the lower-energy photons.
  • The photons are reflected off the active layer.
  • The photons are absorbed by the active layer if the photons' energy is higher than the active layer's band-gap value, which is determined by the particular materials used.
When the energy from the photon is absorbed, electrons and holes slightly decouple to form excitons. These excitons then diffuse to the interface between the n-type and p-type semiconductors (active layer), where electrons and holes fully separate from each other, producing direct current (DC). This current is then carried out of the cell through connections. In the end, arrays of cells convert light energy into DC electricity.

3. What are the main goals of the SUNFLOWER project?

Organic photovoltaics (OPV) represent the newest generation of solar-to-power conversion technologies energies offering the benefits of flexibility, low weight, and freedom of design. OPV can operate under low light conditions. The Sunflower project encompasses the development of OPV technology from end to end. While working on increasing performance in terms of lifetime, efficiency, cost, and sustainability by means of R&D activities on the cell and module levels, Sunflower also addressed usage scenarios that are suited to OPV, as well as the technology’s end-of-life environmental impact. With its 17 partners distributed along the value chain, Sunflower aims at major improvements in three fields: materials, processes, and tools and applications. The Sunflower project team is open innovation driven, working in collaboration with interested end-user companies. It is our aim to be guided by the market in developing the best possible solutions and widely acceptable outcomes within our partnerships. Examples of demonstrators developed within the sunflower project:
  • Portable charger demonstrator for tablet and e-reader devices.
  • Vertical window blind demonstrator — a “retrofittable”, adaptive product for existing buildings.
  • An OPV adhesive film to retrofit indoor windows or OPV laminated between two glasses.
4. What are the intended main applications for OPV?

Due to their flexibility, transparency and light weight key applications can be expected in building applications like shading systems, building facades, windows, and consumer applications like tents, backpacks, clothing and consumer electronic covers.

5. Can OPVs be integrated in building facades?

OPV is expected to be a good fit for building-integrated photovoltaics (BIPV) and net-zero building construction and renovations. Since glass is a primary component of most building envelopes, architects and builders are already familiar with its uses and function. With OPV, it will be possible to add functionality to building components without compromising aesthetics. This increases the value of sustainable architecture and net-zero buildings, as well as the value of the building itself. It is expected that OPV can be an important addition to the growing list of available technologies used in sustainable-building design.

6. How can OPV contribute to a sustainable future energy supply?

OPVs installed on existing infrastructures and buildings generate sustainably electricity from sunlight without additional land use. The unique roll-to-roll production process reduces the production costs and the environmental impact.

7. Which basic materials are used for the production of OPVs?

Aside from the substrate (usually PET foils) and conductive electrodes (usually Ag and ITO), OPV tandem cells are usually made of:
  • Active layers consisting of organic semiconducting polymers. It is where photons are converted into electrical current.
  • Recombination layers consisting of an hole transporting layer (HTL), usually made from polymer PEDOT:PSS and an electron transporting layer (ETL) usually made from zinc oxide nanoparticles.
8. Do OPVs contain scarce metals?

Despite the name OPVs also contain metals for the electrodes, however very small amounts compared to other PV thin film technologies and no rare earth metals.

9. What is the benefit of the multilayer/tandem structure?

One method to increase the light to electricity efficiency of an OPV cell is to add layers with complementary light absorbing spectrum.

10. What means roll-to-roll production?

In the field of OPV, roll-to-roll processing, also known as reel-to-reel processing or R2R, is the process of creating OPV cells and modules on a roll of flexible plastic or metal foil. it can refers to any process of applying coatings, printing, or performing other processes starting with a roll of a flexible material and re-reeling after the process to create an output roll. Once the rolls of material have been coated, laminated or printed they are normally slit to their finished size on a slitter rewinder.

11. Is it possible that OPV pose a risk to the environment or to human health?

Since the active layers producing electricity are fully encapsulated in a plastic barrier foil, it is not assumed that OPV can pose a risk during normal use, even though it was not fully investigated so far. In the SUNFLOWER project, we will study the behavior and eco-toxicity of OPV components under environmentally relevant conditions in use and after disposal.

12. How can the behavior of such components be tested?

Applying different scenarios such as OPV dumped into water, OPV on a landfill, or controlled burning of OPV, the components washed out and potentially reaching the environment are detected and quantified. Additionally, it is analyzed whether such components are partitioned into water, soil, biota or air and whether they accumulate in organisms or not. Like this, environmental concentrations of the components can be estimated giving the basis for a risk assessment.

13. How can the toxicity of such components be tested?

Different established assays will be used in order to decide whether an OPV component is toxic or not. Fish cells (not living creatures!) are going to be exposed to different concentrations of OPV single components as well as mixtures of components directly extracted from existing OPV samples. Various endpoints from cytotoxicity over metal bioavailability to alteration of gene expression will be assessed. Like this, it can be accurately estimated up to which concentrations substances used in OPV can be seen as unproblematic.

14. Why are such experiments carried out while still developing the new OPV?

While developing new products, it is particularly crucial to estimate what possible effect the new product could have on the environment including humans. Especially when OPV should be produced in large quantities in near future it is important to know beforehand whether and to which extent such chemical substances might be problematic. Its environmental impact should be addressed before mass production in order to address questions such as: Should old OPV be recycled or incinerated? What emissions occur while producing, using and disposing OPV? How does the eco-efficiency look compared to other electricity production technologies?