Solution-processable organic semiconductors for integrated photonics applications

In this work, we investigate the optical properties of solution-processable organic semiconductors that are widely employed in the field of large-area, flexible and portable electronics. The refractive index and extinction coefficient of an n-type organic semiconductor (P(NDI2OD-T2)) were measured in the visible and near infrared range by means of spectroscopic ellipsometry. We also demonstrated integration of P(NDI2OD-T2) as a coating film of low-loss silicon oxynitride waveguides (SiON). Results suggest the possibility to integrate solution-processable electronic devices on photonic integrated circuits and to realize organic transistors on photonic platforms

Integration of non-volatile ferroelectric actuators in silicon photonics circuits

In this work, we investigate a novel approach to realize non-volatile phase-actuators integrated in silicon photonic waveguides. We aim to exploit the ferroelectric response of polycrystalline BaTiO3 (poly-BTO) grown by pulsed laser deposition (PLD), whose domain can be re-oriented by applying an external electric field so as to induce a large change of the refractive index. Owing to the polarization remanence of ferroelectric materials, such refractive index variation is partially maintained when the electric field is turned off. Experimental results on poly-BTO demonstrate the possibility to achieve a non-volatile change of the poly-BTO refractive index in the order of 10(-2), which is consistent with a 90 degrees reorientation of the ferroelectric domains. We also integrated thin poly-BTO films in Si waveguides with a low additional propagation loss (<1 dB/mm), enabling the realization of photonic integrated circuits (PICs) with the proposed poly-BTO Si-photonics platform

Non-volatile ferroelectric actuators integrated in silicon photonic circuits

In this work, we investigate a novel approach to realize non-volatile phase- actuators integrated in silicon waveguides. We aim to exploit the ferroelectric response of polycrystalline BaTiO3 (poly-BTO), whose domain can be re-oriented by applying an external electric field so as to induce a large change of the refractive index. Owing to the polarization remanence of ferroelectric materials, such index variation is maintained when the electric field is turned off. Experimental results on poly-BTO demonstrate the possibility to achieve a non-volatile change of the poly-BTO refractive index in the order of 10-2, which is consistent with a 90° reorientation of the ferroelectric domains. We also integrated thin poly-BTO films on Si waveguides with a low additional propagation loss (<1 dB/mm), enabling the realization of PICs with the proposed poly-BTO Si-photonics platform

Ultrafast Hole Transfer from (6,5) SWCNT to P3HT:PCBM Blend by Resonant Excitation

Nowadays, SWCNTs are envisaged to enhance the charge separation or transport of conjugated polymer-fullerene derivatives blends. In this work we studied, by means of ultrafast transient absorption spectroscopy, three components blends in which commercially available SWCNTs are added to the standard bulk heterojunction. We explored three different configurations that give rise to diverse interfacing scenarios. We found strong evidence of a direct hole transfer from photoexcited SWCNTs to the P3HT polymer. The transfer efficiency depends on the interface configuration. It is the highest for the blend where we achieve closer contact between the (6,5) SWCNTs and the polymer. When the polymer blend is deposited on top of the nanotube film or the nanotube film is deposited onto the polymer blend, the process is slowed down due to less or missing interfacing of the carbon nanotubes with the polymer chains. Additionally we demonstrate a cascading effect in the electron path, which stabilizes charge separation by further transferring the electron left behind by hole transfer to the polymer to the adjacent (7,5) SWCNTs. Our results highlight the potential of semiconducting SWCNTs to improving the performance of organic solar cells

Thermoelectric Properties of Highly Conductive Poly(3,4-ethylenedioxythiophene) Polystyrene Sulfonate Printed Thin Films

Organic conductors are being evaluated for potential use in waste heat recovery through lightweight and flexible thermoelectric generators manufactured using cost-effective printing processes. Assessment of the potentiality of organic materials in real devices still requires a deeper understanding of the physics behind their thermoelectric properties, which can pave the way toward further development of the field. This article reports a detailed thermoelectric study of a set of highly conducting inkjet-printed films of commercially available poly(3,4-ethylenedioxythiophene) polystyrene sulfonate formulations characterized by in-plane electrical conductivity, spanning the interval 10-500 S/cm. The power factor is maximized for the formulation showing an intermediate electrical conductivity. The Seebeck coefficient is studied in the framework of Mott's relation, assuming a (semi-)classical definition of the transport function. Ultraviolet photoelectron spectroscopy at the Fermi level clearly indicates that the shape of the density of states alone is not sufficient to explain the observed Seebeck coefficient, suggesting that carrier mobility is important in determining both the electrical conductivity and thermopower. Finally, the cross-plane thermal conductivity is reliably extracted thanks to a scaling approach that can be easily performed using typical pump-probe spectroscopy