Kinetics versus Energetics in Dye-Sensitized Solar Cells Based on an Ethynyl-Linked Porphyrin Heterodimer

Out of the scientific concern on the kinetics versus energetics for rational understanding and optimization of near-IR dye-sensitized solar cells (DSCs), an <i>N</i>-fused carbazole-substituted ethynyl-linked porphyrin heterodimer (<b>DTBC</b>) reported previously by our group was focused upon in terms of photovoltaic, photoelectrochemical, and steady-state and time-resolved photophysical properties in varied electrolyte environments. A primitive attempt to balance the photocurrent against the photovoltage by varying the concentration of the common coadsorbent 4-<i>tert</i>-butylpyridine (TBP) revealed that TBP continuously suppressed injection but provided inadequate compensation in open-circuit voltage (<i>V</i>_oc). This further drew out the perspective of the widely ignored dye–electrolyte interaction in DSCs, specifically the axial coordination of TBP to the central zinc cation in porphyrin sensitizers that may retard electron injection. As an alternative, a TBP-free electrolyte containing guanidinium thiocyanate was developed to realize greatly promoted <i>V</i>_oc with little current sacrifice, thus significantly enhancing overall energy conversion efficiencies. The excited state was protracted to counteract the injection retardation caused by much reduced driving force, setting a successful example of bilateral compromise between kinetics and energetics in near-IR DSCs