Hot hole transfer at the plasmonic semiconductor/semiconductor interface

Localized surface plasmon resonance (LSPR)-induced hot-carrier transfer provides an attractive alternative for light-harvesting using the full solar spectrum. This defect-mediated hot-carrier transfer is identical at the plasmonic semiconductor/semiconductor interface and can overcome the low efficiency of plasmonic energy conversion, thus boosting the efficiency of IR-light towards energy conversion. Here, using femtosecond transient absorption (TA) measurements, we directly observe the ultrafast non-radiative carrier dynamics of LSPR-driven hot holes created in CuS nanocrystals (NCs) and CuS/CdS hetero nanocrystals (HNCs). We demonstrate that in the CuS NCs, the relaxation dynamics follows multiple relaxation pathways. Two trap states are populated by the LSPR-induced hot holes in times (100-500 fs) that efficiently compete with the conventional LSPR mechanism (250 fs). The trapped hot holes intrinsically relax in 20-40 ps and then decay in 80 ns and 700 ns. In the CuS/CdS HNCs, once the CuS trap states have been populated by the LSPR-generated hot holes, the holes get transferred through plasmon induced transit hole transfer (PITCT) mechanism in 200-300 ps to the CdS acceptor phase and relax in 1-8 and 40-50 mu s. The LSPR-recovery shows a weak excitation wavelength and fluence dependence, while the dynamics of the trap states remains largely unaffected. The direct observation of formation and decay processes of trap states and hole transfer from trap states provides important insight into controlling the LSPR-induced relaxation of degenerate semiconductors.

Automated summary

Localized surface plasmon resonance (LSPR)-induced hot-carrier transfer is an attractive option for efficient energy conversion, particularly in the infrared (IR) range. By using femtosecond transient absorption measurements, the researchers observed the dynamics of LSPR-driven hot holes in CuS nanocrystals (NCs) and CuS/CdS hetero nanocrystals (HNCs). In CuS NCs, hot holes relax through multiple pathways, populating two trap states before decaying. In CuS/CdS HNCs, the hot holes are transferred to the CdS phase through plasmon-induced transit hole transfer (PITCT) and relax in a longer timescale. This study provides important insights into controlling LSPR-induced relaxation in semiconductors.