Fabricating binary cathode interface layer by effective molecular electrostatic potential and interfacial dipole to optimize electron transport and improve organic solar cell

• A D-A CIL small molecule based on 1,3-indandione is synthesized. • ESP and μ are used to analyze and optimize CIL. • Efficient binary CIL is fabricated in OSC. • Mechanisms of efficient binary are explored by quantum chemical analysis. For the cathode interface layer (CIL) in organic solar cells (OSC), its molecule quantum chemistry properties are important for the transportation and collection of electrons. To enhance CIL, we design and synthesize a D-A CIL small molecule 2-((5-(4-(2-ethylhexyl)-4H-dithieno[3,2-b:2′,3′-d]pyrrol-2-yl)thiophen-2-yl)methylene)-1H-indene-1,3(2H)-dione (TSY) to optimize the electrostatic potential (ESP) of molecule surface in CIL. Due to the alternating arrangement of optimized positive and negative ESP regions of TSY, the TSY-based PM6:Y6 OSC achieves a J SC of 25.56 mA cm −2 and a PCE of 13.50%. However, the dipole of the PDINO/Al interface facilitates electron transport to the electrode more efficiently than TSY/Al. Therefore, we further constructed TSY:PDINO blend binary CILs to explore the facilitation of electron transport by making good use of CIL molecule ESP and interfacial dipole. Combining the effective electrostatic interaction and electron transfer properties between TSY and PDINO molecules, the TSY:PDINO OSC obtains better performance than the monolithic CIL (J SC = 25.66 mA cm −2 , FF = 73.71%, PCE = 15.52%). This work explains the way of electron transport in the cathode interface layer and provides a method for further optimization of the CIL.