A low-work-function, high-conductivity PEDOT:PSS electrode for organic solar cells with a simple structure

• A low work-function, high conductivity PEDOT:PSS electrode has been prepared.
• A very simple fabrication process of two-step dipping is developed.
• The conductivity of this PEDOT:PSS electrode is up to 1140 S/cm.
• Vacuum-free solar cell based on this electrode exhibits a FF of 61% and a PCE of 4.0%.

We report on a low work-function (WF), high-conductivity poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) electrode by a two-step dipping process. The first dipping into the sulfuric acid is to enhance its conductivity and the second dipping into PEI solution is to lower its work function. After the first dipping, the conductivity of PEDOT:PSS film reaches 1561 S/cm under dipping time of 1 min and the temperature of 60 °C. After dipping into sulfuric acid, the thickness of PEDOT:PSS is reduced to about half but the transmittance was lowered. After the dipping into the PEI solution, the WF of PEDOT:PSS is reduced from 4.9 to 4.0 eV. Although the conductivity were lowered slightly after treated with PEI solution, an electrode with a high conductivity of 1140 S/cm was achieved. The low WF and high-conductivity PEDOT:PSS film is used to fabricate ITO-free, metal-electrode-free and vacuum-free organic solar cells with a simple structure of glass/low-WF PEDOT:PSS/P3HT:ICBA/high WF-PEDOT:PSS, the cells display a fill factor of 61% and a power conversion efficiency of 4.0% under 100 mW/cm2 white light illumination.

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