Effects of Nanogeometry on Carrier Multiplication in 2D Lead Chalcogenide Materials
Laurens Siebbeles a
a Chemical Engineering, Optoelectronic Materials, TU Delft, Julianalaan 136, 2628 BL Delft, The Netherlands, Netherlands
Materials for Sustainable Development Conference (MATSUS)
Proceedings of nanoGe September Meeting 2017 (NFM17)
SE2: Opto-electronics of 2-D Nanostructured Semiconductors: Parabolic vs. Linear Dirac Bands
Barcelona, Spain, 2017 September 4th - 9th
Organizers: Daniel Vanmaekelbergh and Cherie Kagan
Invited Speaker, Laurens Siebbeles, presentation 034
Publication date: 20th June 2016

Absorption of sufficiently energetic photons in a bulk semiconductor leads to hot electrons and holes that usually cool to the band edge by thermal relaxation. In semiconductor nanomaterials this cooling can be intercepted by excitation of additional electrons across the band gap. In this way, one photon generates multiple electron-hole pairs via a process known as Carrier Multiplication (CM), which is of interest for the development of highly efficient solar cells and photodetectors.

We studied charge carrier photogeneration, CM, charge mobility and decay in: a) films of PbSe quantum dots coupled by organic ligands, and b) 2D percolative networks of PbSe quantum dots connected by atomic bonds. The studies were performed using ultrafast pump-probe spectroscopy with optical or terahertz conductivity detection.

The nanogeometry of the material was found to have enormous effects on the charge mobility and the yield of free charges resulting from CM. In 2D percolative PbSe networks CM occurs in a step-like fashion with threshold near the minimum energy of twice the band gap. In these 2D materials the CM efficiency and charge mobility are much higher than for films of QDs that are coupled by organic ligands. The effects of nanogeometry on the efficiency of CM and impact on power conversion in photovoltaic devices will be discussed.

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