Application of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) based on multiple treatments with hot alcohol solvents in organic solar cells

Abstract

Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) materials are widely used to replace common indium tin oxide (ITO) transparent electrodes. However, the conductivity of untreated PEDOT:PSS is unsatisfactory. Thus, enhancing the conductivity of PEDOT:PSS has become an urgent task. In this study, we use hot methanol, 2-methoxyethanol, and ethanol to treat PEDOT:PSS films and explore the effect of multiple treatments with hot alcohol solvents on the electrical conductivity of the films. Results show that the conductivity of the PEDOT:PSS films gradually were increased to 2538 S cm−1, 2273 S cm−1 and 1361 S cm−1 after in the number of treatments using methanol, 2-methoxyethanol and ethanol, respectively. The measurement of absorption for the PEDOT:PSS films before and after treatment revealed that the nonconducting PSS components were effectively removed from the PEDOT:PSS materials using the hot alcohol solvent treatment, which led to the exposure of the PEDOT chains to induce the formation of polaritons (PEDOT+) or bipolaritons (PEDOT2+) and thus enhanced the conductivity of the films. The figure of merit (FoM) values after six times treatments with methanol and 2-methoxyethanol were as high as 56.87 and 51.61, respectively. The FoM of ethanol was 33.58, which did not meet the minimum criteria for commercial application. PEDOT:PSS films treated using methanol and 2-methoxyethanol were applied as transparent electrodes in organic solar cells with power conversion efficiency values of 2.14% and 2.05%, respectively, which reached 87.35% and 83.67% for ITO-based transparent electrodes (2.45% for pure ITO).