Coaxial multishell nanowires with high-quality electronic interfaces and tunable optical cavities for ultrathin photovoltaics

Thomas J. Kempa, James F. Cahoon, Sun Kyung Kim, Robert W. Day, David C. Bell, Hong Gyu Park, Charles M. Lieber

Research output: Contribution to journalArticle

156 Citations (Scopus)

Abstract

Silicon nanowires (NWs) could enable low-cost and efficient photovoltaics, though their performance has been limited by nonideal electrical characteristics and an inability to tune absorption properties. We overcome these limitations through controlled synthesis of a series of polymorphic core/multishell NWs with highly crystalline, hexagonally-faceted shells, and well-defined coaxial p-type/n-type (p/n) and p/intrinsic/n (p/i/n) diode junctions. Designed 200-300 nm diameter p/i/n NW diodes exhibit ultralow leakage currents of approximately 1 fA, and open-circuit voltages and fill-factors up to 0.5 V and 73%, respectively, under one-sun illumination. Single-NW wavelength-dependent photocurrent measurements reveal size-tunable optical resonances, external quantum efficiencies greater than unity, and current densities double those for silicon films of comparable thickness. In addition, finite-difference- time-domain simulations for the measured NW structures agree quantitatively with the photocurrent measurements, and demonstrate that the optical resonances are due to Fabry-Perot and whispering-gallery cavity modes supported in the high-quality faceted nanostructures. Synthetically optimized NWdevices achieve current densities of 17 mA/cm 2 and power-conversion efficiencies of 6%. Horizontal integration of multiple NWs demonstrates linear scaling of the absolute photocurrentwith number ofNWs, as well as retention of the high open-circuit voltages and short-circuit current densities measured for single NW devices. Notably, assembly of 2 NW elements into vertical stacks yields short-circuit current densities of 25 mA/cm 2 with a backside reflector, and simulations further show that such stacking represents an attractive approach for further enhancing performance with projected efficiencies of >15% for 1.2 μm thick 5 NW stacks.

Original languageEnglish
Pages (from-to)1407-1412
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume109
Issue number5
DOIs
Publication statusPublished - 2012 Jan 31

Keywords

  • Nanodevices
  • Nanomaterials
  • Nanophotonics
  • Optical nanocavities
  • Solar cells

ASJC Scopus subject areas

  • General

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