The introduction of a rigid triptycene moiety as a three-dimensional (3D) bulky framework into a thiophene-fused porphyrin dye (TrpZnP) for dye-sensitized solar cells (DSSCs) is reported. The triptycene unit effectively suppresses dye aggregation and charge recombination with the redox shuttle. However, DSSCs based on TrpZnP exhibited a significantly lower power conversion efficiency (PCE, 3.57%) compared to the reference porphyrin dye TrpZnP (9.84%), primarily due to reduced short-circuit current density and incident photon-to-current efficiency (IPCE). Transient absorption spectroscopy reveals that the dye regeneration efficiency of TrpZnP is markedly decreased, indicating inefficient electron transfer from the redox shuttle to the oxidized dye. This reduced regeneration efficiency is attributed to steric hindrance and weakened electronic coupling arising from the bulky and electronically insulating sp 3 -hybridized triptycene framework. These findings demonstrate that while 3D steric blocking effectively suppresses charge recombination, excessive bulkiness can hinder dye regeneration. This study highlights the importance of balancing steric protection and electronic coupling in the molecular design of high-performance porphyrin sensitizers.
Higashino et al. (Fri,) studied this question.