Single-nanowire Si solar cells

Abstract

Solar cells based on arrays of CVD-grown Si nano-or micro-wires are being considered as a potentially low-cost route to implementing a vertical multijunction cell design via radial p-n junctions. This geometry has been pre dicted to enable efficiencies competitive with planar mul ticrystalline Si designs, while reducing the materials and processing costs of solar cell fabrication [1]. To further assess the potential efficiency of cells based on this de sign, we present here experimental measurements of mi nority carrier diffusion lengths and surface recombination rates within nanowires via fabrication and characterization of single-wire solar cell devices.Furthermore, we con sider a potential Si wire array-based solar cell design, and present device physics modeling of single-wire photo voltaic efficiency. Based on experimentally observed dif fusion lengths within our wires, we model a radial junction wire solar cell capable of 17% photovoltaic energy con version efficiency.

Growth of vertically aligned Si wire arrays over large areas (>1cm2) with Au and Cu catalysts

“…Diffusion of gold into bulk silicon at our VLS growth temperatures of 1000-1050°C leads to carrier lifetimes of Ͼ1 ns, 17 which combined with carrier mobilities expected for the observed dopant densities, 13,18 indicates minority carrier diffusion lengths of ജ1 m. This is in agreement with our near-field scanning optical microscope measurements of the minority carrier diffusion length of Aucatalyzed Si wires. 13 As shown in the present work, photolithography is an ideal method for enabling uniform arrays of wires of this diameter to be grown over large areas. In costsensitive applications such as photovoltaics, it would ulti-FIG.…”

“…27 We have also demonstrated operation of a single wire p-n junction Si solar cell. 13 We expect that these arrays may also be useful as photonic crystals. Finally, it should be possible to extend this methodology to alternative lithographic techniques, as well as to making wire arrays of materials that cannot currently be fabricated with top-down methods.…”

Energy-Conversion Properties of Vapor-Liquid-Solid–Grown Silicon Wire-Array Photocathodes

“…The wire arrays were then sealed face down at the end of glass tubing through which the wire had previously been fed using Hysol 1C epoxy. Black nail polish was used to define the active area of the wire-array device (~0.1 cm 2 ). Prior to photoelectrochemical measurements, the p-Si wire arrays were etched as follows: 10 s 10 % aq.…”

Tuning Light Absorption in Core/Shell Silicon Nanowire Photovoltaic Devices through Morphological Design

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] For example, the optical properties of arrays of nano-and microscale wires have been exploited for enhanced light absorption in photovoltaic devices, [16][17][18][19] however, the ability to substantially manipulate absorption in individual nanoscale structures has not been well established. In order to quantify optical resonances supported in individual NWs, scattering [20][21][22] and absorption cross-sections 5,6,11,[23][24][25][26] have been measured or calculated.…”

“…6,11,23 We recently reported an absolute EQE value of up to ~1.2 using core/shell Si NWs with a size of ~300 nm. 6 By comparison, EQE values of ~0.15 have been reported for microscale devices based on Al-Si Schottky junctions 23 and values of ~1.1 for devices with coaxial p-n junctions that included a back-side reflector. 11 Several reports of relative EQE values have been reported for Si and Ge nanowire devices acting as photodetectors.…”