Increasing the Open-Circuit Voltage of Dye-Sensitized Solar Cells via Metal-Ion Coordination

Considerable efforts are dedicated to increasing the open-circuit voltage (V_oc) of dye-sensitized solar cells (DSSCs) by slowing charge recombination dynamics using atomic layer deposition, alkyl-substituted dyes, coadsorbents, and other strategies. In this report, we introduce metal-ion coordination to a metal oxide bound dye as an alternative means of increasing V_oc. Metal-ion coordination has minimal influence on the photophysical and electrochemical properties of the N3 dye, but presumably because of increased steric hindrance at the interface, it slows charge recombination kinetics and increases V_oc by upwards of 130 mV relative to the parent N3 DSSC. With respect to the nature of the metal ion, the trend in decreasing short-circuit current (J_sc) and increasing V_oc correlates with the charge of the coordinated metal ion (M^IV → M^III → M^II). We attribute this trend to electrostatic interactions between the metal cation and I^- or I₃^-, with the more highly charged cations maintaining a higher concentration of mediator anions in proximity to the surface and, as a result, increasing the regeneration and recombination rates.