Innovative Plasmon-induced Carrier Separation

Researchers at University of Tokyo have proposed a promising new strategy to improve the efficiency of optoelectronic devices.

In an invited paper for a special section on hot carrier energy harvesting and conversion in the Journal of Photonics for Energy, Professor Tetsu Tatsuma and doctoral students Kazutaka Akiyoshi and Koichiro Saito report on a new type of hybrid Au-TiO₂-Ag nanoparticle that leads to more efficient plasmon-induced carrier separation (PICS).

Hot carrier generation and separation processes, albeit inefficient, have been recognized in classic semiconductor physics for a long time. Achieving high power-conversion efficiency, however, is still a challenge and is less than 1% for hot-carrier photodetectors or photovoltaic devices using these plasmonic effects.

Researchers coated the ligand-protected silver nanocubes with a TiO₂ film and a 5-nm-thick gold layer.

When colloidal metal nanoparticles are used for PICS, their organic protecting layer often suppresses electron transfer from the nanoparticles to the semiconductors. Although the protecting layer can be removed by annealing, the nanoparticles may easily lose their anisotropies.

Tatsuma and his team addressed this issue by coating the ligand-protected silver nanocubes with a TiO₂ film and a 5-nm-thick gold layer. This led to about 20 times enhancement in the observed photocurrent, which could be attributed to the accelerated electron transfer from the silver nanocubes to TiO₂ via the highly conductive gold layer.

Another possible mechanism is due to the localized field generated around the Ag nanocubes, which significantly enhances light absorption within the 5-nm-thick gold film and leads to more efficient PICS at the gold/TiO₂ interface. This latter mechanism seems to be the dominant one based on a comparison between the photocurrent and the optical absorption spectra.

The findings in the open-access paper, “Enhancement of plasmon-induced charge separation efficiency by coupling silver nanocubes with a thin gold film,” provide a promising strategy to develop functional materials for hot carrier energy harvesting and conversion applications based on PICS.

Source: dx.doi.org/10.1117/1.JPE.6.042505

–Qiaoqiang Gan is an assistant professor at the University at Buffalo (USA) and a member of the editorial board of the Journal of Photonics for Energy.

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