Improvement in Half-Life of Organic Solar Cells by Using a Blended Hole Extraction Layer Consisting of PEDOT:PSS and Conjugated Polymer Electrolyte

In this study, we fabricated conventional structured organic solar cells (OSCs) by introducing a hole extraction layer (HEL) that consisted of poly­(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) and conjugated polymer electrolyte (CPE) poly­[9,9-bis­(4′-sulfonatobutyl)­fluorene-alt-thiophene] (PFT-D). PFT-D has a −SO₃^– functional group that acts as a conjugate base against the −SO₃H of PSS. In addition, the molecular dipole of PFT-D can screen the Coulombic attraction between PEDOT chains and PSS chains. By blending PEDOT:PSS and PFT-D, the acidity of the HEL solution and changes to the surface morphology and potential of the HEL film as a function of exposure time in air were reduced. As a result, the half-life of the OSC fabricated with blended HEL was five times better at room temperature and 40% humidity without encapsulation as compared to the pristine PEDOT:PSS-based device.