SOCl 2 enhanced photovoltaic conversion of single wall carbon nanotube/n-silicon heterojunctions

Abstract

We report solar cells based on high-density p-n heterojunctions between single wall carbon nanotubes (SWCNTs) and a n-type silicon wafer. Chemical modification by thionyl chloride of the SWCNT coating films was found to significantly increase the conversion efficiency by more than 45% through adjusting the Fermi level and increasing the carrier concentration and mobility. Electron-hole pairs are optically excited in the numerous heterojunctions formed between SOCl2-treated SWCNTs thin coating and n-type silicon substrate, and then split and transported through SWCNTs (holes) and n-Si (electrons), respectively.

Implementation of antireflection layers for improved efficiency of carbon nanotube–silicon heterojunction solar cells

“…Later, post-treatments of the device, such as with thionyl chloride (SOCl 2 ) or acids, were developed to improve PCE [11,12]. Similar devices were also reported using the CNT deposition method of Wu [4] which involves vacuum filtration of CNT onto mixed cellulose ester (MCE) membranes which can then be removed by dissolution with acetone [13].…”

Carbon nanotubes for organic/inorganic hybrid solar cells

“…nanometer thin SiOx insulator between the Si and metal, minority charge carriers will be transported through the insulating layer by CNT fibers [119]. By applying a series of doping and gating methods such as SOCl 2 treatment [116], ionic liquid electrolyte infiltration and electronic gating [120,121] as well as nitric acid doping [122], the power conversion efficiencies of the CNT-Si cells have been continuously pushed from initially about 1.3% to 13.8% (within the last several years.…”

Electrical transport properties of isolated carbon nanotube/Si heterojunction Schottky diodes

“…One is the Schottky barrier at the Pd/CNT interface and the other is the conduction band discontinuity at the CNT/n + -Si heterojunction interface. In the band diagram, CNT is an intrinsic semiconductor with band gap of 0.6 eV and electron affinity of 4.5 6 eV and work function of Pd is 5.2 eV. The band diagram indicates that the Pd electrodes deliver a good ohmic contact to CNTs for holes but not for electrons.…”

“…In addition, multiple electron-hole pairs associated with the higher subbands at low temperatures could enhance the device performance. 11 While the SWNT/Si heterojunction could play a crucial role in the CNT based devices, the measurements of electrical transport properties on the heterojunctions between isolated SWNT and Si have yet not been made because most of the work has been done by using CNT composite film 5,6,10 or multiwalled CNTs. 8,9 Figure 1 shows an outline of the CNT/Si diode fabrication process.…”

“…5 This device is ready for integrating the existing Si solar cells which hold a dominant share of the market and an even higher efficiency could be achieved by fabricating multi-junction solar cells. The CNT/Si heterojunction has attracted great interest not only for solar cells [5][6][7] , but also for photodetectors [8][9][10] in the wide wavelength ranging from ultraviolet to near-infrared. For these applications, single walled CNT (SWNT) could provide even higher performance due to the strong absorption at the wide wavelength range.…”