Performance, Stability and Environmental Impact of Organic Solar Cells: Towards Technology Scale-up

Abstract

The effects of global climate changes are progressively observable on the environment. Their direct correlation with the CO2 emission coming from the fossil fuel combustion and industrial processes elucidates the urgent need of renewable energies. In this context, organic photovoltaics (OPVs) attracts much attention because of the cost-competitiveness and the new device functionalities over existing solar cells. Indeed, the interesting properties of organic materials open the road to the economically sustainable production of flexible and light-weight devices, which also meet aesthetical requirements as semi-transparency and color-tunability. This Ph.D. thesis focuses on the performance, stability and environmental impact of solution-processed polymer solar cells (PSCs). In a preliminary part, the development of novel materials, the optimization of the processing conditions and a deeper understanding of the device physics elucidate the pathways towards the enhancement of the PSCs efficiency. However, PSCs still present some issues of stability under operation conditions, which slow down the widespread commercialization of this technology. To this end, part of the thesis discusses some specific aspects related to the stability of critical materials/layers of organic solar cells. In particular, the light stability of different active materials and ZnO layers is investigated in order to provide guidelines for the development of advanced materials for PSCs. Then, the impact of the processing conditions on the thermal stability of the resulting photovoltaic devices is studied. In particular, the effect of the replacement of common chlorinated solvents with a “greener” analogous is investigated both in terms of device efficiency and thermal stability. Finally, a contribution to the understanding of state-of-the-art tandem architectures is reported as a perspective for the large scale deployment of highly performing solar cells. The analysis of these crucial aspects of OPVs provides the basis for the development of improved devices heading to the widespread deployment of this technology.