Vertical Phase Separation for Highly Efficient Organic Solar Cells Incorporating Conjugated‐Polyelectrolytes

Abstract

AbstractHybrid organic solar cells are made through a simple one‐pot coating process with conjugated polyelectrolytes (CPEs), poly[9,9‐bis(4′‐sulfonatobutyl)fluorenealt‐thiophene‐doped (PFT‐D). The hybrid active layer incorporated with PFT‐D shows vertical phase separation by self‐assembled properties of PFT‐D, which result from a molecular dipole between the conjugated backbone and the side chain. The hybrid active layer with PFT‐D shows that homogeneous morphology, surface potential properties, and hydrophobic surface properties favor for enhancing photovoltaic performance. These results are identified by contact angle characteristics, X‐ray photoelectron spectroscopy (XPS) profiling, and X‐ray diffraction (XRD), atomic force measurement (AFM), and electrostatic force measurement (EFM) analyses. With fullerene based hybrid active layer, the power conversion efficiency (PCE) reaches to 8.7% with the enhanced short‐circuit current density (J SC), open‐circuit voltage (V OC), and fill factor (FF). The hybrid device with PFT‐D has a higher stability with a lower reduction ratio of 5.74% compared with only bulk‐heterojunction device (with reduction rate of 30.15%) and incorporating poly(3,4‐ethylene dioxythiophene)‐poly(styrene sulfonate) (PEDOT:PSS) device (with reduction rate of 10.84%). These results are also found in nonfullerene based system (PCE of 10.8%) and other conjugated polyelectrolytes system (PCE of 8.4%). These results have the potential of significantly contributing to the upsizing and commercialization of organic solar cells.