Nickel(II) Nitrate Hole‐Transporting Layers for Single‐Junction Bulk Heterojunction Organic Solar Cells with a Record 19.02 % Efficiency

A facile strategy was developed here to improve the film quality of nickel‐based hole transporting layer (HTL) for efficient organic solar cell (OSC) applications. To prevent the agglomeration of Ni(NO3)2 during film deposition, acetylacetonate was added into the precursor solution, which led to the formation of an amorphous and glass‐like state. After thermal annealing (TA) treatment, the film‐forming ability could be further improved. The additional UV‐ozone (UVO) treatment continuously improved the film quality and increased the work function and conductivity of such HTL. The resulting TA & UVO modified Ni(NO3)2 & Hacac HTL produced highly efficient organic solar cells with exciting power conversion efficiencies of 18.42 % and 19.02 % for PM6 : BTP‐eC9 and D18 : BTP‐Th devices, respectively, much higher than the control PEDOT : PSS devices. A facile strategy was developed to improve the film quality of a solution processed nickel(II) nitrate hole transporting layer, which realized a record efficiency of 19.02 % for the binary blend bulk heterojunction organic solar cells.