Quantum-Dots-on-Silicon Hybrids: Towards Energy Transfer Based

Nanostructured Photovoltaics.

 

Yuri Gartstein

 

Department of Physics, The University of Texas at Dallas

 

Energy transfer (ET) based hybrids comprise components with a clear separation of the functionalities: one component of the nanostructure is chosen for its strong light-matter interaction while the other for its high charge-carrier mobilities. Conceptually reminiscent of photosynthesis, solar light is envisioned to be harvested in the well absorbing component followed by exciton diffusion and ET across the interface with the subsequent separation and transport of charge carriers entirely within the high-mobility semiconductor component. The crucial energy exchange between the components is enabled by the strong near-field electromagnetic interactions. The excitonic sensitization is particularly appealing for crystalline silicon as it would eliminate the weak solar light absorption in the indirect band-gap Si as a defining design factor thus possibly leading to ultrathin silicon devices.

 

In this talk I will discuss recent progress of our collaborative team from Departments of Physics and Materials Science and Engineering in studying ET from photoexcited colloidal quantum dots (QDs) into Si substrates. The quantitative analysis of the time-resolved photoluminescence reveals that this ET can be highly efficient over a broad range of wavelengths including into ultrathin (~ 100 nm) Si nano membranes. It is demonstrated that ET occurs by means of both non-radiative (NRET) and radiative (RET) mechanisms exhibiting different distance and wavelength dependences. While NRET corresponds to the direct production of electron-hole pairs in Si, in the RET process the QD excitons preferentially decay into photonic modes propagating within Si (waveguiding modes in thin layers).We find that our systems make an interesting “case study” for the general problem of modification of radiative lifetimes of electric-dipole emitters by polarizable environments. As a further step towards exploration and utilization of optically thick QD assemblies, we provide evidence for the concept of directed ET by analyzing energy relaxation pathways through QD-size-gradient bilayer structures on Si substrates.

 

http://www.utdallas.edu/news/2012/10/9-20061_Researchers-Seek-Way-to-Make-Solar-Cells-Ultra-Thi_article-wide.html

 

This research has been supported by grants from NSF (DMR-1207123) and DOE/BES (DE-SC0010697).

 

Host: Prof. V. Podzorov