NOVEL MATERIAL DESIGN AND MANIPULATION STRATEGIES FOR ADVANCED OPTOELECTRONIC APPLICATIONS

Il mio progetto di dottorato è stato focalizzato sui semiconduttori organici per applicazioni fotovoltaiche e di fotorivelazione. Inizialmente ho lavorato sul controllo morfologico di blende binarie di molecole organiche e fullereni usando la cosiddetta strategia dei pigmenti latenti. In particolare ho lavorato sull'ingenierizzazione dello strato attivo di celle solari organiche a eterogiunzione. Ho dimostrato una nuova strategia per controllare la segregazione di fase in film sottili di molecole elettron donatrici e fullereni, introducendo nel sistema un network di legami di idrogeno attivato termicamente. Successivamente ho studiato i processi di accumulazione di carica all’interfaccia tra acqua e un semiconduttore polimerico per applicazioni biomediche per mezzo di nanocristalli colloidali biemissivi con alta sensibilità verso agenti elettronattrattori. In fine, ho dedicato l’ultima parte del mio lavoro all’approfondimento delle possibili applicazioni di questa classe di nanocristalli come sensori raziometrici di pH intracellulare e come vernici per il monitoraggio ottico della pressione.
My PhD has been focused on organic semiconductors for photovoltaics and photodetecting applications. Initially, I worked on the control of the morphology in binary blends of small organic molecules and fullerenes using the so called latent pigment approach. Subsequently, I investigated the charge accumulation and polarization effect occurring at the interface between water and a polymeric semiconductor used as optical component in retinal prosthesis by means of inorganic colloidal nanocrystals featuring a ratiometric sensing ability for electron withdrawing agents. As a last part of the work, I focalized on the applications of these nanocrystals as ratiometric sensors for intracellular pH probing and pressure optical monitoring. Specifically, during the first part of my PhD, I worked in the field of organic photovoltaics on the morphology engineering of the active layer of small molecules bulk-heterojunction solar cells. I demonstrated a new strategy to fine tune the phase-segregation in thin films of a suitably functionalized electron donor blended with fullerene derivatives by introducing in the system a post-deposition thermally activated network of hydrogen bonds that leads to improved stability and high crystallinity. Moreover, this process increases the carrier mobility of the donor species and allows for controlling the size of segregated domains resulting in an improved efficiency of the photovoltaic devices. This work revealed the great potential of the latent hydrogen bonding strategy that I subsequently exploited to fabricate nanometric semiconductive features on the film surface by using a very simple maskless lithographic technique. To do so, I focalized a UV laser into a confocal microscope and used the objective as a “brush” to thermically induce a localized hydrogen bonding driven crystallization with diffraction limited resolution. My work on organic semiconductors continued with a study on the surface polarization driven charge separation at the P3