Molecular Design\nEngineering Regulates the Ground-State\nPassivation Ability of Benzophenone Derivatives in Perovskite Solar\nCells

Intramolecular hydrogen bonding (H-bonding) involved\nin the excited-state\nproton transfer (ESPT) process results in benzophenone derivatives\n(BPDs) with an excellent ability to passivate defects. However, the\nBPDs are in a continuing dynamic transition process between the ground\nstate and the excited state under light radiation conditions. The\nground-state BPDs may lose their ability to passivate defects, resulting\nin an increased defect density of the perovskite. Therefore, enhancing\nthe passivation ability of the ground-state BPDs can help to achieve\nthe full passivation ability of their ground state to excited state.\nHerein, we have researched the various BPDs by density functional\ntheory and found that intramolecular H-bonding can weaken the passivation\nability of ground-state BPDs, but intramolecular H-bonding is indispensable\nin the ESPT process. To address the issue, we investigated the influence\nof electron-donor properties and dipole moments of hydroxyl (−OH),\nmethoxy (−OCH<sub>3</sub>), and <i>n</i>-octyloxy\n(−OC<sub>8</sub>H<sub>17</sub>) groups in BPD molecules on\ntheir coordination capacity through molecular design engineering.\nUltimately, 2-hydroxy-4-<i>n</i>-octyloxy-benzophenone (UV5)\nwith strong electron-donor <i>n</i>-octyloxy (−OC<sub>8</sub>H<sub>17</sub>) and elongated carbon-chain structure was selected\nas an additive, which enhances the passivate defect capability in\nboth the ground and excited states. As a result, the UV5-based champion\ndevice achieved a power conversion efficiency (PCE) of 24.46% and\nremained at 75% of the initial PCE with exposure to UV light. This\nwork focuses on the defect passivation capability of ground-state\nBPDs for the first time and opens a new concept for applying BPDs\nin PSCs.