Interlayer surface energy control for high-efficiency printed organic photovoltaic cells

Abstract

The surface properties of the substrate play a crucial role in regulating the morphology of active layers coated atop and the resulting photoelectronic properties in solution-processed organic photovoltaic (OPV) cells. However, current studies on the relationship between the surface free energy (γ_S) of the substrate and film morphology of the active layers remain superficial. Here, we present an effective method for tuning γ_S by incorporating NiO nanoparticles into commercial PEDOT:PSS hole transport layers (HTLs). Furthermore, we systematically perform the film-forming process and characterize the morphology to quantitatively establish the relationship between surface energy, liquid precursor film length, film-forming kinetics, and morphology. The results indicate that increasing the γ_S of the substrate can elongate the liquid precursor film length, extend the phase separation time, and enhance the crystallinity of the active layer. Consequently, the blade-coated 1.03 cm² OPV cells based on the PEDOT:PSS:NiO HTL and PBQx-TCl:eC9-2Cl active layer yield a record PCE of 18.70% (certified as 18.51% by the National Institute of Metrology, China); the manufactured 23.60 cm² OPV modules achieve an outstanding PCE of 16.5%. This work contributes to a deeper understanding of the interface characteristics and morphological control of the blade-coated large-area active layers toward high-efficiency OPV cells.