ADDITIVES FOR THE IMPROVEMENT OF THE PERFORMANCE OF ORGANIC AND HYBRID PHOTOVOLTAIC

During the last decades, the climate change induced to an intense policy debate on the future of our planet and the impact of the most common energy sources on the environment. It is known that the most traditional energy sources are no longer sufficient to satisfy the high energy demand without spoiling the earth environment. Therefore, the urgent need to move from fossil to renewable energy sources increased the interest in wind, biomass and solar technologies. Photovoltaic represents a highly promising technology to tackle this global energy issue. Within this context, Organic photovoltaics (OPV) have attracted broad interest from the scientific community because of the recent impressive advances in terms of performance and efficiency. The progress in the new classes of materials’ synthesis and the countless developments in the perspective of scale-up with flexible and transparent supports, make organic photovoltaics very attractive for marketing and inclusion in everyday objects. Even though the device efficiencies increased rapidly, further progresses are fundamental to improve the device stability and performance for the long term and wider usage. In this Thesis the crucial role of additives was investigated to tackle the most common issues in OPVs manufacturing. Firstly, in accordance with the industrial partner Eni S.p.A., some innovative polymeric materials have been synthetized, selecting the main representative moieties from the most promising and attractive monomers in the literature. These materials have been used as an additive, with both standard commercial and Eni property blends to gain more insight into the role played by the additives in the active layer. Having a good solution-processable formulation is crucial during the device fabrication, mostly in the industrial large scale deposition. With this respect, to decrease the imperfection in the final thin-film and improve the ink formulation, some additives were added to fluidify and improve the donor-acceptor blend. Focusing the study at Eni on the industrial perspective, the introduction of an additional innovative class of hole transport layers (HTL) has been studied in both lab and large scale. The most widely used material as HTL is the molybdenum oxide; in order to deposit it on the active layer is necessary to use the thermal evaporator, a process that requires high vacuum and high temperature. Yet, for the industrial perspective, it should be preferable to have all solution-processable materials resulting in all printable devices by means of continuous deposition processes. In this regard, PEDOT:PSS is the most commonly used printable HTL. Differently from its counterpart, PEDOT:PSS affects the device performances giving lower PCE. This behaviour can be ascribed to the different work function of PEDOT and to wetting ability issues. In this context, three innovative molybdenum and vanadium polyoxometallates have been tested as a secondary layer in combination with PEDOT. The studied bilayer in lab-scale strongly improved the device performances resulting comparable and even higher than e-MoOx. Moreover, these materials have been tested in flexible devices fabricated by means of slot-die coating in sheet to sheet, resulting impressively efficient and also with higher performances than the evaporated counterpart. Moving toward the main OPV categories, the present Thesis also focuses also on the role of the additive as third component in ternary solar cells. In this work, two fullerene derivatives have been used as additive acceptor or third component in inverted solar cells with a PCE of over 14%. The introduction of the fullerene derivative astonishingly enhanced the long-term stability of the blend retaining its PCE even after six months in air condition, while the binary blend lost over 70% of the initial PCE. Remarkably, the same results were obtained fabricating the devices in air condition avoiding glove box controlled ambient.