Enhancing the efficiency of near-infrared iridium (III) complexes-based OLEDs by auxiliary ligand functionalization

Sensitizers of Metal Complexes with Sulfur Coordination Achieving a Power Conversion Efficiency of 12.89%

“…38,39 The electron-withdrawing ability of the auxiliary electron acceptor can be regulated by the strength of the coordination bond between the central metal and the ligand. 40 The stronger the coordination bond, the greater the electron-withdrawing ability of the complex, which facilitates intramolecular electron transfer. 41−44 According to the soft and hard acid−base principle, the strength of the coordination bond is regulated by the ligand atom and metal ions.…”

“…The insertion of an auxiliary electron acceptor in between the electron donor and π-bridge can modulate the highest occupied molecular orbital (HOMO) and HUMO energy levels and energy gap ( E g ) of the dye molecule, reduce the electron recombination, and improve absorption spectra and photovoltaic performance of the dye sensitizer. − Generally, quinoxaline (Qu), , phthalimide, benzotriazole (BTZ), , diketopyrrole (DPP), and benzothiadiazoles (BTD) , have been used as auxiliary electron acceptors. Organic dye sensitizers have many advantages, such as higher V oc , the availability of higher performance dyes in a wide range of colors, etc., but there are also some disadvantages, such as poor thermal stability, low molar extinction coefficients, and poor PCE enhancement. , However, adopting metal complexes to replace the above organic compounds as auxiliary electron acceptors can improve the thermal stability of dyes sensitizer, improve the molar extinction coefficient, enhance intramolecular charge transfer (ICT) ability, and strengthen their electron-withdrawing ability. , The electron-withdrawing ability of the auxiliary electron acceptor can be regulated by the strength of the coordination bond between the central metal and the ligand . The stronger the coordination bond, the greater the electron-withdrawing ability of the complex, which facilitates intramolecular electron transfer. − According to the soft and hard acid–base principle, the strength of the coordination bond is regulated by the ligand atom and metal ions. − For a series of soft acid metal ions Ni­(II), Cu­(II), Zn­(II), Cd­(II), and Hg­(II), the coordinating ability of soft base sulfur (S) with them is stronger than that with oxygen (O) and nitrogen (N), which can cause the coordinate bond of these metal with sulfur (S) to be stronger than that with oxygen (O) and nitrogen (N) and therefore will enhance the electron-withdrawing ability of auxiliary electron acceptor and improve their photovoltaic performance.…”

Two Novel Neutral Cyclometalated Iridium(III) Complexes Based on 10,11,12,13-Tetrahydrodibenzo[a,c]phenazine for Efficient Red Electroluminescence

“…In addition, heavy atom effect can effectively enhance the progress of intersystem crossing from excited-singlet state to excited-triplet state. For instance, in the iridium(III) complex-based OLEDs, both excited-singlet and excited-triplet state excitons can be captured simultaneously, thus obtaining 100% internal quantum efficiency theoretically [ 18 , 19 , 20 ]. Red emission is one of the important primary colors for display applications, and has aroused tremendous interest.…”

Rational design of orange-red iridium(iii) complexes by an isomer engineering strategy for improved performance of white organic light-emitting diodes

“…Iridium(III) complexes are being rapidly developed due to their superior quantum efficiency, short triplet excited-state lifetime, and tunable color gamut. [14][15][16][17][18] The central iridium(III) core can induce a strong spin-orbit coupling effect that facilitates the intersystem crossing process, leading to an efficient emission of the resulting devices. 16 Therefore, extensive research efforts have been devoted to constructing varied iridium(III) complexes for meeting the requirements of practical applications in the past few decades and investigating the relationship between the structure and EL performance.…”