Fabricating Binary Cathode Interface Layer by Effective Molecular Electrostatic Potential and Interfacial Dipole to Optimize Electron Transport and Improve Organic Solar Cell

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. The common CIL molecule PDINO has high local polarity and severely separated molecule orbitals, which limits intramolecular charge transfer. To enhance CIL, we design and synthesize a D-A CIL small molecule 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 higher J SC (26.97 mA cm -2 vs. 25.76 mA cm -2 ) and a PCE similar to PDINO (14.17% vs. 14.58%). However, the dipole of the PDINO/Al interface facilitates electron transport to the electrode more efficiently than TSY/Al. Therefore, we further constructed PDINO/TSY, TSY/PDINO double-layers, and TSY:PDINO blend binary CILs to explore the facilitation of electron transport by making good use of CIL molecule ESP and interfacial dipole. On the one hand, the TSY/PDINO promotes electron transport while PDINO/TSY inhibits by the mainly negative ESP surface of TSY and the positive one of PDION. On the other hand, the interfacial dipole of PDINO/Al facilitates the electron collection. As result, the TSY/PDINO OSC obtains better performance than the monolithic CIL (J SC =26.37 mA cm -2 , FF=73.89%, PCE=15.80%), while the performance of PDINO/TSY is lower (J SC =24.84 mA cm -2 , FF=61.12%, PCE=12.18%). This work explains the way of electron transport in the cathode interface layer and provides a method for further optimization of the CIL