(342a) Development of Double-Gyroid Nanowire Arrays for Photovoltaics

Multiple exciton generation (MEG) has been observed and studied in PbS and PbSe quantum dots (QDs). However, despite many advances in the understanding of the photoconversion physics and electron transport in quantum dot arrays, the grand challenge of developing photovoltaic devices that exhibit IQE greater than 100% has yet to be realized. Quantum dots are zero dimensional objects and must be electronically coupled in order to extract any photocurrent. A broader class of structures may be sought in pursuit of achieving this goal that have 0D photophysics but electronic transport more similar to 3D structures [1]. Here, we present experimental and theoretical results on solar cells based on highly ordered “double-gyroid” arrays of PbS quantum wires. The wire segments that compose the ordered array are 4 nm in diameter and intersect at y-junctions every 12 nm. These unique nanomaterials are fabricated using self-assembled double-gyroid nanoporous films as the nanowire template [2,3]. 2D grazing incidence small-angle x-ray scattering (GISAXS) patterns exhibit 96 diffraction peaks from the nanoscale order. The patterns are indexed with a (211) oriented cubic unit cell with Ia-3d symmetry and lattice constant equal to 18 nm. Thus, the PbS wire segments are interconnected with crystallographic periodicity. We have used an envelope formalism with parameters fitted from PbS QD data to calculate the electronic structure of the PbS double-gyroid wire array. The electronic density of states shows a significant blue-shift in the band gap and additional small gaps in the conduction and valence band [4]. All-inorganic Schottky junction and interpenetrated p-n junction photovoltaic devices have been fabricated with a variety of contacts and device architectures. Currently, the best devices show poor power conversion efficiencies, but show unusually high open circuit voltages (as high as 0.45 eV). The presentation will focus on the electronic structure calculations, photovoltaic device fabrication, and device performance.

References:

[1]  Hillhouse H.W. & Beard M.C., “Solar Cells from Colloidal Nanocrystals: Fundamentals, Materials, Devices, and Economics,” Current Opinion in Colloid & Interface Science, 14, 245-259 (2009).

[2]  Urade VN, Wei TC, Tate MP, Kowalski JD, & Hillhouse HW, “Nanofabrication of double-gyroid thin films,” Chem. Mater. 19 (4), 768 (2007).

[3]  Tate, M.P., Urade, V.N., Gaik, S.J., Muzzillo, C.P., Hillhouse,* H.W., “How to Dip-Coat or Spin-Coat Nanoporous Double-Gyroid Silica Films with EO19-PO43-EO19 Surfactant (Pluronic P84) and Know it Using a Powder X-ray Diffractometer,” Langmuir 26 (6), 4357-4367 (2010).

[4] Khlebnikov S & Hillhouse HW, “Electronic Structure of Double-Gyroid Nanostructured Semiconductors: Perspectives for Carrier Multiplication Solar Cells,” Phys. Rev. B 80, 115316 (2009).