Eeva-Leena Rautama

High performance low temperature carbon composite catalysts for flexible dye sensitized solar cells

Roll-to-roll manufacturing of dye sensitized solar cells (DSSCs) requires efficient and low cost materials that adhere well on the flexible substrates used. In this regard, different low temperature carbon composite counter electrode (CE) catalyst ink formulations for flexible DSSCs were developed that can be simply and quickly coated on plastic substrates and dried below 150 °C. The CEs were investigated in terms of photovoltaic performance in DSSCs by current-voltage measurements, mechanical adhesion properties by bending and tape tests, electro-catalytic performance by electrochemical impedance spectroscopy and microstructure by electron microscopy. In the bending and tape tests, PEDOT-carbon composite catalyst layers exhibited higher elasticity and better adhesion on all the studied substrates (ITO-PET and ITO-PEN plastic, and FTO-glass), compared to a binder free carbon composite and a TiO2 binder enriched carbon composite, and showed lower charge transfer resistance (1.5-3 Ω cm(2)) than the traditional thermally platinized CE (5 Ω cm(2)), demonstrating better catalytic performance for the tri-iodide reduction reaction. Also the TiO2 binder enriched carbon composite showed good catalytic characteristics and relatively good adhesion on ITO-PET, but on ITO-PEN its adhesion was poor. A DSSC with the TiO2 binder enriched catalyst layer reached 85% of the solar energy conversion efficiency of the reference DSSC based on the traditional thermally platinized CE. Based on the aforementioned characteristics, these carbon composites are promising candidates for replacing the platinum catalyst in a high volume roll-to-roll manufacturing process of DSSCs.

Cationic ordering and interface effects in superlattices and nanostructured materials

Thin film methods offer a versatile approach to overcome the natural preference for disorder or low-dimensional ordering in certain materials by controlling the location of cations in tailored oxide multilayers. Artificial heterostructures have hence been utilized to probe how interlayer coupling and cation ordering at the interface affect magnetic or transport properties. Recently, it was shown that LaTiO/SrTiO3 superlattices exhibit metallic conductivity, similar to a bulk solid solution of La1−xSrxTiO3, even though the heterostructure is based on two insulators [1]. In this contribution, a series of highquality (LaVO3)6m(SrVO3)m superlattices (Figure 1) with a nominal composition close to La6/7Sr1/7VO3 has been grown on [001]-oriented SrTiO3 substrates using standard pulsed-laser deposition [2]. When m=1, the bulk-like insulating resistivity of La6/7Sr1/7VO3 is obtained while for m≥2 the superlattices display a metallic behaviour. The comparison of the superlattice periodicity with the known coherence length of charge carriers across the interface of perovskite oxide heterostructures is used to understand this insulator-metal transition.