Modifying the nanostructures of PEDOT:PSS/TiCT composite hole transport layers for highly efficient polymer solar cells

Two-dimensional (2D) transition metal carbides, MXenes, typically represented by Ti 3 C 2 T X , have shown great promise in optoelectronic devices due to their metallic electrical conductivity, large surface area, superior hydrophilicity and excellent transparency. Herein, to improve the conductivity of polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) films, we incorporate solution-processable 2D Ti 3 C 2 T X nanosheets into PEDOT:PSS to fabricate PEDOT:PSS/Ti 3 C 2 T X composite layers, and polymer solar cells (PSCs) with PEDOT:PSS/Ti 3 C 2 T X composite films as hole transport layers (HTLs) are fabricated for the first time. The nanostructures and the corresponding hole injection properties of PEDOT:PSS/Ti 3 C 2 T X composite layers are systematically evaluated. Based on the non-fullerene PBDB-T:ITIC system, a power conversion efficiency (PCE) of 11.02% is obtained for the device with PEDOT:PSS/Ti 3 C 2 T X as the HTL, which is improved by 13.5% compared to that of the control device with pure PEDOT:PSS as the HTL (9.72%). When using the PM6:Y6 system as the active layer, the PCE of the device based on PEDOT:PSS/Ti 3 C 2 T X is improved to 14.55% from 13.10% for the PEDOT:PSS reference device. 2D Ti 3 C 2 T X nanoflakes with higher conductivity construct additional charge transfer pathways between the PEDOT nanocrystals and induce conformational transition of PEDOT from a coil to a linear/expanded-coil structure, leading to an improvement in conductivity and device performance. Interestingly, PEDOT:PSS/Ti 3 C 2 T X based devices also exhibit enhanced long-term stability compared to PEDOT:PSS based devices. These results show that PEDOT:PSS/Ti 3 C 2 T X composite films have a promising prospect in high efficiency organic optoelectronics. PEDOT:PSS/Ti 3 C 2 T X composite hole transport layers with fine-tuned nanostructures are facilely fabricated, which shows obviously higher efficiency and stability than that of the control device with pure PEDOT:PSS as HTL.