Hierarchical TiO_1.1Se_0.9-wrapped carbon cloth as the TCO-free and Pt-free counter electrode for iodide-based and cobalt-based dye-sensitized solar cells

A titanium oxide-selenide (TiO_1.1Se_0.9) composite material was successfully obtained on a flexible substrate of carbon cloth (CC); this TiO_1.1Se_0.9/CC electrode was used as the counter electrode (CE) in a dye-sensitized solar cell (DSSC). Each carbon fiber in the CC was wrapped with a composite layer of TiO_1.1Se_0.9, and the composite layer contained TiO_1.1Se_0.9 nanospheres and one-dimensional (1D) nanorods. Thus, each carbon fiber with its TiO_1.1Se_0.9 layer has a hierarchical core-shell structure, in which the carbon fiber acts as a one-dimensional conductive core for electron transfer and the TiO_1.1Se_0.9 layer around the fiber functions as an electro-catalytic shell. In iodide-based electrolyte, the DSSC with the TiO_1.1Se_0.9/CC exhibits a power conversion efficiency (η) of 9.47%, which is higher than cells with CEs of Pt/CC (7.75%) and pristine TiO₂/CC (4.90%). Under dim light conditions, the best TiO_1.1Se_0.9/CC electrode rendered its cell an η of 10.00% at 0.5 sun and the best η of 10.39% at 0.1 sun. In cobalt-based electrolytes, a DSSC with the TiO_1.1Se_0.9/CC shows an attractive η of 10.32% at 1.0 sun, the best η of 10.47% at 0.5 sun, and an impressive η of 10.20% at 0.1 sun. The earth abundant and low-cost TiO_1.1Se_0.9 is a promising alternative to Pt for the CE of a DSSC in both iodide and cobalt electrolytes.