Structure of Diethyl-phosphonicacid Anchoring Group Affects the Charge-Separated State in Iridium(III)-Complex functionalized NiO Surface
in: ChemPhotoChem (2020)
Cyclometalated Iridium(III) complexes, i.e. [Ir(C^N)2(dppz)][PF6], bearing either two or four -CH2PO(OH)2 anchoring groups (IrP2dppz or IrP4dppz) are explored as photosensitizers for p-type dye sensitized solar cell (DSSC). The synthetic route is described and the Iridium(III) complexes are characterized with respect to their electrochemical and photophysical properties. The modified anchoring ligand geometry exploited in this work does not only alter the electronic nature of the complex, i.e. it destabilizes the LUMO energetically, but foremost improves the grafting ability towards the NiO surface. The photoinduced long-lived charge separated state (CSS) at the NiO|IrPxdppz interface is of different nature comparing the two complexes. For IrP2dppz and IrP4dppz the electron density of the CSS dominantly resides on the dppz and the C^N ligand, respectively. The stability of the CSS can be correlated to the solar cell performance in NiO-based p-DSSCs, which yield conversion efficiencies highest among the class of Iridium(III) complexes developed for p-DSSC.