Ti3CN MXenes-induced N-N couplings modifies perylene-diimide-based cathode interlayers for 20 % efficiency organic solar cells

Abstract

The perylene-diimides-based cathode interlayers exhibit unique properties, such as optimal energy levels, strong electron affinities, and insensitivity to film thickness. However, the inherent aggregation features of these molecules result in uneven film surfaces that are difficult to avoid, potentially impairing the devices’ performance. Herein, we propose the N-N couplings strategy for improving the charge extraction ability in the cathode interlayers in organic solar cells by incorporating nitrogen functionalities Ti₃CN with the representative cathode materials, PDIN and PDINN. Upon introducing 1 % Ti₃CN by weight into PDIN, The Ti within the Ti₃CN structure acts as an electron donor, losing electrons to generate a positive charge that attracts the amino end groups of PDIN, leading to N-N couplings. The N-N interactions resulted in a smoother layered surface and enhanced conductivity of the cathode interlayer, thereby increasing the charge extraction property. When these layers were applied in devices comprising PM6 and Y6 derivatives, the dark current leakage was suppressed, and charge extraction processes were optimized, leading to enhanced short-circuit current density and fill factor, thus, an optimum power conversion efficiency of 20.0 %. Our findings on the N-N couplings strategy offer valuable insights into developing hybrid cathode interlayers for highly efficient organic solar cells.