Solid-state synthesis of a conducting polythiophene as efficient Pt-free thin film counter electrode for dye-sensitized solar cells

•I doped PEDOT can be synthesized through solid-state polymerization.•The conductivity and the catalytic activity are enhanced after I doped in PEDOT.•I doped PEDOT CEs shows an η of 6.38%.

An efficient Pt-free counter electrode (CE) based on poly(3,4-ethylenedioxythiophene) (PEDOT) film for dye-sensitized solar cells (DSSCs) has been developed via solid-state polymerization (SSP) approach. The polymerization was simply initiated by sintering the monomer, 2,5-diiodo-3,4-ethylenedioxythiophene (DIEDOT), at the temperature of 135 °C. Furthermore, DIEDOT is not only quite suitable and economic for large scale synthesis, but also very stable in air. Under optimized conditions, the power conversion efficiency of a DSSC with a N719-sensitized TiO2 photo-anode and the SSP-PEDOT CE is 6.38% measured under standard 1 sun illumination (100 mW cm−2, AM 1.5).