Investigation of exciton photodissociation, charge transport and photovoltaic response of poly(N-vinyl carbazole):TiO₂nanocomposites for solar cell applications

Abstract

The photogeneration of charge carriers in spin-coated thin films of nanocrystalline (nc-)TiO(2) particles dispersed in a semiconducting polymer, poly(N-vinylcarbazole) (PVK), has been studied by photoluminescence and charge transport measurements. The solvent and the TiO(2) particle concentration have been selected to optimize the composite morphology. A large number of small domains leading to a large interface and an improved exciton dissociation could be obtained with tetrahydrofuran (THF). The charge transport mechanism and trap distribution at low and high voltage in ITO/nc-TiO(2):PVK/Al diodes in the dark could be identified by current-voltage measurements and impedance spectroscopy. The transport mechanism is space charge limited with an exponential trap distribution in the high voltage regime (1-4 V), whereas a Schottky process with a barrier height of about 0.9 eV is observed at low bias voltages (<1 V). The current-voltage characteristics under white illumination have shown a dramatic increase of the short circuit current density J(sc) and open circuit voltage V(oc) for a 30% TiO(2) volume content corresponding to the morphology exhibiting the best dispersion of TiO(2) particles. A degradation of the photovoltaic properties is induced at higher compositions by the formation of larger TiO(2) aggregates. A procedure has been developed to extract the physical parameters from the J-V characteristics in the dark and under illumination on the basis of an equivalent circuit. The variation of the solar cell parameters with the TiO(2) composition confirms that the photovoltaic response is optimum for 30% TiO(2) volume content. It is concluded that the photovoltaic properties of nc-TiO(2):PVK nanocomposites are controlled by the interfacial area between the donor and the acceptor material and are limited by the dispersion of the TiO(2) nanoparticles in the polymer.

Tunable of Open-circuit Voltage In Bilayer Hybrid Solar Cells by Binary Polymer Blends

“…It has been demonstrated that there is often an interface activation energy barrier Φ B at the heterojunction. At present, the formation of the Φ B are usually explained as a result of the energy level bending by the vaccum level misalignments at the heterojunction or the formation of interface chargetransfer states, [11] and Φ B can be evaluated from the dark reverse saturation current in dark J-V characteristic by: [12,13] …”

Progress in Organic Photovoltaic Fibers Research

“…Organic solar cells have many advantages such as potential to be semi-transparent, manufacture on both large or small areas compatible with mass production and low-cost, production possibility with continuous coating and printing processes on lightweight and flexible substrates (for example textiles), ecological and low-temperature production possibilities (Dennler et al, 2006a;Dennler & Sariciftci, 2005). Polymer heterojunction organic solar cells have attracted much attention because of their potential applications in large area, flexible and low-cost devices (Park et al, 2009;Chang et al, 2009;Dridi et al, 2008;Peet et al, 2009;Oey et al, 2006;Yu et al, 2008). Polymer based thin films on flexible and non-flexible substrates can be achieved by various printing techniques (see Fig.…”

Synthesis of Poly(2,7‐carbazole)s and Derivatives

“…Recent reports have shown that PVK could be very useful as a host material in white-organic light-emitting diodes (WOLEDs) [29,41], in combination with other layers, because of its high energy blue-emissive singlet excited state and the absence of low energy triplet state [30]. Moreover, PVK has also been used in dye-sensitized solar cells blended with TiO 2 as the electron donor and hole-transporting material [31][32][33][34]42]. The interest has grown up recently because of new promising performances in PCs, FETs, and LEDs for carbazole derivatives and related polymers [35].…”