(Invited) Atomic Layer Deposition of Core-Shell Nanowires for Solar Energy Conversion Devices

Recently, there has been a dramatic increase in research of nanoscale materials for energy conversion and storage applications due to several advantageous features such as high surface areas, short transport distances, novel optical phenomena, and tunable material properties.  However, with these benefits come challenges. In particular, the ability to precisely control the properties of surfaces and heterogeneous interfaces at the nanoscale limits the performance of many of these devices, and requires novel approaches. This problem becomes increasingly important as dimensions decrease, as the surface-to-volume ratios contiunally increase with decreasing feature size.

Semiconductor nanowires (NWs) posses several advantages for energy conversion devices owing to their high surface areas, tunable compositions, and efficient charge transport properties [1].  However, precise control of surfaces and interfacial properties is crucial to maximize charge-transfer efficiency across the interfaces between NWs and the surrounding device components, while minimizing undesirable side reactions and recombination losses.  One technique that has been increasingly explored for surface and interfacial engineering of nanostructured energy conversion and storage devices is Atomic Layer Deposition (ALD).  This gas-phase process allows for highly conformal deposition of a wide variety of materials with sub-nm precision in material thickness and tunable chemical composition.  By coating the surfaces of NWs with ALD, core-shell structures can be fabricated with atomic-scale control.  This combination of conformality and thickness control facilitates precise tuning of the electronic, optical, thermal, and chemical properties of nanowire surface to optimize their interfaces in energy conversion devices.

This talk will present several examples of using ALD to fabricate highly-controlled core-shell for energy conversion and storage devices, with an emphasis on solar energy applications.  Examples include quantum-dot sensitized nanowires [2], earth abundant core-shell NW photovoltaics at the singe nanowire and array level [3], and coating of nanowire surfaces with passivation layers and co-catalysts for photoelectrochemical water splitting [4-5].  Additionally, the use of ALD for precise control of heterogeneous interfaces in hierarchical nanomaterial synthesis will be presented. The importance of fully understanding ALD surface chemistry will be discussed from a theoretical and experimental perspective.  The talk will conclude with a perspective on future directions and challenges for widespread commercial adaption of these technologies.

References:

[1]  N. P. Dasgupta et al. “25th Anniversary Article: Semiconductor Nanowires - Synthesis, Characterization, and Applications”, Adv. Mater. 26, 2137 (2014).

[2]  N. P. Dasgupta et al. “Atomic Layer Deposition of Lead Sulfide Quantum Dots on Nanowire Surfaces”, Nano Lett., 11(3), 934 (2011).

[3]  S. Brittman, Y. Yoo, N. P. Dasgupta, S.-I. Kim, B. Kim and P. Yang, “Epitaxially Aligned Cuprous Oxide Nanowires for All-Oxide Single-Wire Solar Cells” Nano Lett. 14, 4665 (2014).

[4]  N. P. Dasgupta, C. Liu, S. Andrews, F. B. Prinz and P. Yang, “Atomic Layer Deposition of Platinum Catalysts on Nanowire Surfaces for Photoelectrochemical Water Reduction”, J. Am. Chem. Soc. 135, 12932 (2013).

[5]  J. Resasco, N. P. Dasgupta, J. Rosell, J. Guo, and P. Yang “Uniform Doping of Metal Oxide Nanowires Using Solid-State Diffusion” J. Am. Chem. Soc. 136, 10521 (2014).