An EPR investigation on photoactive materials for solar cells

In this work a variety of organic semiconducting materials, suitable as charge transport layers in organic and hybrid perovskite solar cells are investigated using Electron Paramagnetic Resonance Spectroscopy. The reason for the extensive employment of this technique stems from the ubiquitous presence of paramagnetic species in the ground state or after photoexcitation materials used in photovoltaic devices. All the investigated systems are potentially able to efficiently transport charges and participate in the photophysics of a solar cell, while stabilizing the perovskite layer. For this reason, this thesis focuses on multiple EPR spectroscopic characterizations of several classes of materials, aimed at linking the different molecular structures of these compounds to their photophysical and electrical properties. A series of derivatives composed off phosphonic-acid-carbazole units (PACz) were examined to evaluate the effect of substituents on the properties of their radical cations and also the photogeneration of their photoexcited triplet states. Another group of molecular arylamino-based systems is investigated to assess, by conventional and temperature-dependent EPR, the influence of various factors, such as structure, oxidation state, and environmental conditions like solvent and temperature, affecting the intramolecular electron transfer in the radical cations. Also, their photophysics was assessed focusing on the impact of molecular structure toward the generation and decay of their triplet states. In two novel push-pull dyes the photoinduced electron transfer to titanium oxide was explored by EPR steady state and time-resolved methods, trying to rationalize their photoactivity when deposited on perovskites materials. Lastly, the EPR spectroscopic investigation addressed thin films of P3HT blended with properly functionalized reduced graphene oxide (rGO) to evaluate morphological and photoactive properties when the polymer is deposited as thin film on different substrates, including photoactive perovskite.