Energy level tuning of aromatic polyamines by [2+2] cycloaddition-retroelectrocyclization for the optimization of device performances

The highest occupied molecular orbital (HOMO) level of hole-transporting polymeric materials was tuned by postfunctionalization based on a highly-efficient (2 + 2] cycloaddition-retroelectrocyclization (CA-RE) reaction. After the CA-RE reaction, the HOMO level of an aromatic polyamine, determined by the electrochemical first oxidation potential, was lowered from - 5.30 eV to - 5.37 eV. This enabled the smooth hole injection from the perovskite layer of organic-inorganic perovskite solar cells. Although the hole mobility of the aromatic polyamine, determined by the space-charge limited current (SCLC) method, decreased by this postfunctionalization, the energy level adjustment was more significant for the improvement of the solar cell performances. The device based on the postfunctionalized polyamine with the HOMO level of - 5.37 eV showed more than twice the photoconversion efficiency than that based on the precursor polyamine with the HOMO level of - 5.30 eV.