| AVS 62nd International Symposium & Exhibition | |
| Nanometer-scale Science and Technology | Tuesday Sessions |
| Session NS+EN+SS-TuA |
| Session: | Nanophotonics, Plasmonics, and Energy |
| Presenter: | Sara Rupich, University of Texas at Dallas |
| Authors: | S.M. Rupich, University of Texas at Dallas A.V. Malko, University of Texas at Dallas Y.N. Gartstein, University of Texas at Dallas Y.J. Chabal, University of Texas at Dallas |
| Correspondent: | Click to Email |
In order to meet the world’s growing energy demand, harvesting energy from the sun is necessary. While silicon-based solar cells remain the industry standard, hybrid Si/nanocrystal (NC) structures exhibit significant promise for the development of the next generation of photovoltaic devices. In most current NC-based photovoltaics, photons are absorbed, separated and extracted in the NC layer; however, conversion efficiencies are limited by interface quality and carrier mobility. Hybrid Si/NC structures offer an alternative approach. In these structures, light is absorbed in the NC layer and transferred via efficient excitonic radiative (RET) and non-radiative (NRET) energy transfer into the underlying Si substrate where charge extraction and collection occurs. In order to utilize such structures, the controllable deposition of tens of layers of NCs needs to be realized where the composition of each layer can be varied. While many techniques exist to deposit NCs on substrates (i.e. spin coating, dropcasting), these methods result in thick films with limited control over the composition. Composition controlled structures need to be built up one layer at a time.
Here, we present the controllable deposition of dense, NC multilayer structures on Si and SiO2 substrates via evaporation-driven self-assembly at the air-liquid interface. Using a layer-by-layer approach, CdSe/ZnS NC multilayers were assembled, up to 15 layers in thickness. Extensive spectroscopic (UV-vis absorbance, photoluminescence (PL), ellipsometry) and microscopic (scanning electron microscopy and atomic force microscopy) characterization provided evidence for the successful deposition of high quality NC multilayers in each cycle. Additionally, the NCs were found to retain their quantum yields in the multilayers structures indicating that the deposition process does not introduce additional interface trapping centers and showing their promise for integration into optoelectronic devices. Using time-resolved PL measurements, a gradual increase in the average measured NC PL lifetime was observed as a function of layers for NC multilayers on Si surfaces. This behavior was confirmed by theoretical modeling and is indicative of the gradual reduction in ET efficiency as a function of distance and.
As this process is applicable to NCs of different size, shape and composition, the fabrication of band gap graded multilayers structures is possible, which would enable energy harvesting schemes based on directed energy flows.