Enhanced control of self-doping in halide perovskites for improved thermoelectric performance

Metal halide perovskites have emerged as promising photovoltaic materials, but, despite ultralow thermal conductivity, progress on developing them for thermoelectrics has been limited. Here, we report the thermoelectric properties of all-inorganic tin based perovskites with enhanced air stability. Fine tuning the thermoelectric properties of the films is achieved by self-doping through the oxidation of tin (ΙΙ) to tin (ΙV) in a thin surface-layer that transfers charge to the bulk. This separates the doping defects from the transport region, enabling enhanced electrical conductivity. We show that this arises due to a chlorine-rich surface layer that acts simultaneously as the source of free charges and a sacrificial layer protecting the bulk from oxidation. Moreover, we achieve a figure-of-merit (ZT) of 0.14 ± 0.01 when chlorine-doping and degree of the oxidation are optimised in tandem

Enhanced low-temperature thermoelectrical properties of BiTeCl grown by topotactic method

We developed a topotactic strategy to grow BiTeCl single crystals. Structural characterization by means of X-ray diffraction was performed, and the high crystallinity of the material was proven. Measurements of the thermoelectrical coefficients electrical resistivity, thermoelectric power and thermal conductivity show an enhanced room temperature power factor of 20 mu W cm(-1) K-2. The high value of the figure of merit (ZT = 0.17) confirms that BiTeCl is a promising material for engineering in thermoelectric applications at low temperature. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved

Tailoring thermal conduction in anatase TiO2

Thermal conductivity (κ) plays an essential role in functional devices. It is advantageous to design materials where one can tune κ in a wide range according to its function: single-crystals and nanowires of anatase polymorph of titanium dioxide, broadly used in applications ranging from photovoltaics, reflective coatings to memristors, have been synthesized in large quantities. Here we identify a new, strong diffusion mechanism of heat by polaronic structures due to oxygen vacancies, which considerably influences both the absolute value and the temperature dependence of κ. The additional decrease of κ is achieved in anatase nanowires organized into foam, where porosity and the quasi-one-dimensional size-effect dramatically hinder the propagation of heat, resulting in an extremely low κ = 0.014 W/Km at room-temperature. Doping this anatase foam could herald promising applications, in particular in thermoelectricity