Achieving High Efficiency Silicon-Carbon Nanotube Heterojunction Solar Cells by Acid Doping

Abstract

Various approaches to improve the efficiency of solar cells have followed the integration of nanomaterials into Si-based photovoltaic devices. Here, we achieve 13.8% efficiency solar cells by combining carbon nanotubes and Si and doping with dilute HNO(3). Acid infiltration of nanotube networks significantly boost the cell efficiency by reducing the internal resistance that improves fill factor and by forming photoelectrochemical units that enhance charge separation and transport. Compared to conventional Si cells, the fabrication process is greatly simplified, simply involving the transfer of a porous semiconductor-rich nanotube film onto an n-type crystalline Si wafer followed by acid infiltration.

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.…”

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

“…Since the CNT layer is thin, photons can reach the underlying n-type silicon and be absorbed to produce electron-hole pairs (exciton) which then diffuse into a depletion region created at the CNT-Si interface. Under the influence of a builtin potential created from band-bending due to equilibration of the Fermi levels at the junction, these excitons are separated into free holes and electrons which can be collected at the CNT layer and silicon substrates, respectively [9].…”

“…Application of a gate potential to alter electronic junction properties (via ionic liquid electrolyte) was reported to adjust efficiency between 4 and 11 % reversibly and dynamically, and this was interpreted to be due to the modulation of carbon nanotube Fermi level and improvement of the homogeneity of the silicon depletion region [14]. Even higher PCE solar cells (13.8 %) have been reported in which nanotubes were doped in situ by nitric acid (HNO 3 ), where a decrease of tube-tube resistance and shifting of Fermi level down into the valence band contributed to high efficiency [9]. In another work, an insulating polymer poly(dimethylsiloxane) (PDMS) layer, which acted as both an antireflection (AR) and surface protection layer, was deposited onto the active area and the resultant encapsulated device showed improved PCE (> 10 %) and stability (relatively stable with 20 days in air) [15].…”

Interconnecting Carbon Nanotubes for a Sustainable Economy

“…CNT thin films and mats are currently being tested as components of these photovoltaic devices. This section of the chapter will explore how the CNTs have been used to enhance dye-sensitized [3], CdTe [4] and silicon [5] based solar cells, and address some the concerns about the race to produce novel photovoltaic devices and the toxic warnings from the past that may ultimately define the balance between safety and efficiency.…”