Transient Spectroscopic Dynamics of Excitons and Polarons in the P3HT:FLR Blend

Abstract

Transient absorbance spectroscopy is a crucial technique used to understand the excited-state behavior of materials and investigate the photoexcitation dynamics of organic donor–acceptor blends. Here, we use the potential blend of donor polymer poly-3-hexylthiophene (P3HT) and nonfullerene acceptor 1,6,7,10-tetramethylfluoranthene (FLR) to study the charge generation and recombination by transient absorption spectroscopy. We gained new insights into the functioning of the P3HT:FLR blend considering varying excitation energies. First, we show that the rise of polarons in the P3HT:FLR blend is dependent on the excitation energy. This is consistent with the understanding that the enhanced exciton delocalization facilitates the dissociation of excitons in bulk-heterojunction solar cells. Second, the excitation energy-dependent kinetic study provides an insight into charge generation and the recombination mechanism in the P3HT:FLR blend by identifying the recombination pathway. The obtained results in this study suggest that the long-lived polaron formation in P3HT:FLR is higher than that in the fullerene system, which enables it to generate more free charge carriers by reducing nonradiative recombination.

The effect of the intramolecular disorder on hot exciton dynamics in polymer solar cells

“…Up to now, different strategies have been proposed experimentally and theoretically to modulate the hot exciton dynamics. 15,17,18 Among them, the roles of temperature 17 and photoexcitation conditions 15,18 have been highlighted. Moreover, it should be noted that due to the high degree of conformational freedom of molecular chains and the irregular interchain entanglement, polymers usually form highly disordered structures in the nanometer to the micrometer length range.…”