Hot
carriers rapidly lose kinetic energies on a subpicosecond time
scale, posing significant limitations on semiconductors’ photon-conversion
efficiencies. To slow the hot carrier cooling, the phonon bottleneck
effect is constructed prevalently in quantum-confined structures with
discrete energy levels. However, the maximum energy separation (ΔEES) between the energy levels is in a range
of several hundred meV, leading to unsatisfactory cooling time. To
address this, we design a novel organic semiconductor capable of forming
intermolecular charge transfer (CT) in J-aggregates, where the lowest
singlet excited state (S1) splits into two states due to
the significant interplay between the Coulomb interaction and intermolecular
CT coupling. The ΔEES between the
two states can be adjusted up to 1.02 eV, and an extremely slow carrier
cooling process of ∼72.3 ps was observed by femtosecond transient
absorption spectroscopy. Moreover, the phonon bottleneck effect was
identified in organic materials for the first time, and CT-mediated
J-aggregation with short-range interactions was found to be the key
to achieving large ΔEES. The significantly
prolonged carrier cooling time, compared to <100 fs in the isolated
molecule (10–6 M), highlights the potential of organic
molecules with diversified aggregation structures in achieving long-lived
hot carriers. These findings provide valuable insights into the intrinsic
photophysics of electron–phonon scattering in organic semiconductors.