Poly(Styrene Sulfonate) Free Poly (3,4-Ethylenedioxythiophene) as a Robust and Solution-Processable Hole Transport Layer for Organic Solar Cells

We first time report poly(styrene sulfonate) (PSS) free poly(3,4-ethylenedioxythiophene) (PEDOT) as a novel solution-processable hole transport layer (HTL) for organic solar cells. The transparent and conducting PEDOT thin film was obtained by solid state polymerization (SSP) of 2,5-dibromo-3,4-ethylenedioxythiophene (DBEDOT) on ITO coated glass substrate (by heating of the monomer at 60 degrees C for overnight). The thicknesses of the obtained thin films were optimized by using different concentrations of DBEDOT in chlorobenzene during spin coating. Two different combinations of active layers such as poly(3-hexylthiophene): phenyl-C-61-butyric acid methyl ester (P3HT:PC61BM) and poly[N-9'-heptadecanyl-2,7-carbazole-alt-5,5(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)]: phenyl-C-71-butyric acid methyl ester (PCDTBT:PC71BM) were used for device fabrication. Power conversion efficiencies were achieved up to 0.71% and 1.70% in a simple geometry of ITO/ssp-PEDOT/active layer/Al under ambient conditions. The potential importances of the ssp-PEDOT as an HTL are robust, stable, PSS free and solution-processable for organic solar cells.