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

Hybrid 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.