Large scale roll-to-roll produced organic photovoltaic devices: manufacturing, lifetime and environmental impact

The world energy production has risen intensely during the last decades bringing human development until the point that our current society cannot function without it. Two-thirds of global greenhouse gas emissions, along with other releases which can be highly harmful to humans and the ecosystem come from electricity production.

Consequentially, the need for clean, renewable and sustainable ways of energy production rises up, due to pollutants and the finite nature of fossil fuels. Solar energy is by far the most abundant renewable resource available and fulfils the requirements of a truly green energy resource. The most efficient form of harvesting energy from the sun is through photovoltaics (PV) devices, for which the most used technology require high amounts of materials and energy, and brings several drawbacks to overall solar energy production such as high price and long energy payback times (EPBT).

The development of new PV technologies brought a new horizon to the PV industry in terms of cost and applications. Organic photovoltaics (OPV) has the shortest EPBT and can avoid the use of high energy demanding processes and hazardous elements, with low environmental impacts over its entire life cycle of the system, i.e., from its manufacturing through its deployment and operation up to its final disposal.

As OPV comes about as an emerging technology just about to be commercialised, this thesis demonstrates the reproducible production of vacuum-, indium tin oxide (ITO)-, and silver-free OPV. The fast roll-to-roll (R2R) processing of these devices can bring such low costs to OPV that it balances its lower efficiencies and lifetime compared with other PV technologies.

Such silver-free devices use carbon as electrode material instead and represent a potential truly green technology. To evaluate the truly environmental friendliness of OPVs, four electrodes alternatives have been assessed using the life-cycle assessment (LCA) methodology, indicating that metal based electrodes are the major contributors to the environmental burden of the OPV modules.

One of the main challenges for OPV relies on the short operational lifetime. Two OPV technologies using electrodes with the lower energy demand and metal content (carbon and silver nanowires) in a total of eight different OPV structures have their stability behaviour analysed in a total of seven standard conditions.

Some outdoor tests lasted for more than 700 days. Many of them presented outstanding operational lifetimes compared with the most recent reports. Such lifetimes are already compatible with applications such as in seasonal greenhouses and electronic devices. The challenges associated with end-of-life management of large scale installation of OPV must be addressed as the technology comes closer and closer to reality.

OPV modules with and without silver installed outdoors had their emission of silver and zinc to the aqueous environment (rain, fog, dew) measured and quantified in a rain runoff setup simulating their use phase. Such studies included intact and deliberately damaged OPV modules exposed to natural weather conditions in Denmark for six months.

Endof-life management was assessed simulating a landfill, or an uncontrolled disposal, at the end-of-life. The setup consisted of buried intact and shredded OPV modules in soil columns simulating best and worst case, respectively. The results revealed the recycling of silver in the disposal is mandatory from an environmental point of view for silver containing OPV.

Finally, the LCA was also used as a tool to quantitatively compare the potential environmental advantage of a product over another. A power bank product including a portable OPV panel brings the possibility of the battery to be charged from the sun and not only from the grid. The environmental burden of this and two other well-established power banks products are assessed through LCA.

One of them also includes a solar panel (made of amorphous silicon – a-Si) and the other is a regular power bank without it. The results point out the advantages in charging the battery using the sun instead of the grid, differences between the products when they are used and disposed in Denmark or in China, and indicate improvements focused on the products ecodesign.

Even though the OPV based product is still at a pilot production scale and have a much more detailed inventory with primary data collection, it scores lower than the a-Si based in some impact categories. Such products with portable solar panels have also the advantage of giving the power of lowering the environmental impact in the hands of the user, and for OPV it is a first step as a commercially available technology contributing to clean and sustainable energy production.