Influence of solvent treatment with fluoro compounds on the properties of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) polymer as a hole transport layer in polymer solar cells

Abstract

We prepared high conducting poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) by solvent additives for using as a hole transport layer (HTL) in polymer solar cells (PSCs). PEDOT:PSS films treated with fluoro compounds of hexafluoroacetone (HFA) and hexafluoroisoproponal (HFIPA) with various concentrations show a significant enhancement in electrical conductivity without compromising optical transparency. The conductivity increased from 0.2 to 1053 and 746  S/cm after 4 vol. % HFA and 6 vol. % HFIPA treatments, respectively. The high performance of the PEDOT:PSS layer is attributed to preferential phase segregation of PEDOT:PSS with HFA and HFIPA solvent mixture treatment methods. The improved performance of PSC was dependent on the structure of organic solvents and the concentration of fluoro compounds in PEDOT:PSS solution. Using these optimized layers, conjugated PSCs with a poly[[9-(1-octylnonyl)-9H-carbazole-2,7-diyl]-2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2,5 thiophenediyl] polymer:[6,6]-phenyl-C71-butyric acid methyl esters (PCDTBT:PC 71 BM ) bulk heterojunction have been produced. The high power conversion efficiency (PCE) of 4.10% and 3.98% were observed for PEDOT:PSS films treated with 4 vol. % HFA and 6 vol. % HFIPA treatments, respectively. The obtained results show that PEDOT:PSS optimized with HFA and HFIPA organic solvents can be a very promising candidate for transparent anode buffer layer in the low cost organic solar cell devices.