Engineering D-A polymer polarity in heterostructure photocatalyst for improved interfacial charge transfer efficiency

Abstract

Conventional inorganic semiconducting photocatalysts are facing insufficient light harvesting as well as severe charge recombination problems. Constructing heterostructures is a well-known strategy for accelerating charge separation, especially when hybridizing with donor–acceptor (D-A) conjugated polymers, which features tunable bandgap and high absorption coefficient, these problems can be simultaneously eased. However, the singlet exciton binding energy of D-A polymers is too high for efficient exciton dissociation. In this work, we designed fluorine substituted D-A polymer PxF-T (x = 1, 2, 4) and studied polarity effect on the interfacial charge transfer in CdS/PxF-T. By adjusting the numbers of F substitutions in the acceptor unit, the electron-withdrawing ability of A site can be improved while the polarity of the whole organic molecules is tuned. Among 1, 2, 4 substitutions, the photocatalytic hydrogen production results show that the single F substitution induces the most efficient hydrogen production activity of 6327.7 μmol·g−1·h−1, which is 30.1 times higher than that of pristine CdS. In addition, electrochemical test and time-resolved transient absorption study further confirmed the improved charge transfer activity. Density functional theory calculations reveal that the F introduction induced polarity change is responsible for the improved interfacial charge transfer efficiency, however the increased number of substitutions is not necessarily favorable for improved polarity. This work uncovers the effect of fluorine substitution on the intramolecular polarity of D-A semiconductor for the fabrication of efficient hybrid photocatalysts.