Download Previous work on CVD

As-grown arrays of SiNWs
Previous work on CVD-grown SiNWs
Single SiNW
NATURE| Vol 449| 18 October 20070
•Removed from the growth substrate and
APL 91, 233117 2007
laid on a foreign substrate
•wafer-scale active areas, consists in directly integrating
•Contacts are formed by optical or e-beam
an as-grown array of vertically aligned SiNWs
lithography
•Efficiency is about 0.1%
The novelty of this study is planarization of the SiNW array
(100)-oriented
•n-type SiNWs fabricated by CVD
As-grown
D ~ 40 nm
After SOP coated
Final structure
Illuminated with 100 mW/cm2
Shot-circuit current 17mA/cm2
Open-circuit voltage 250 mV
FF= 44%
Efficiency= 1.9%
Control experiment with p-type SiNWs
In order to improve the efficiency of organic solar cells, one approach, addressed in this paper, will be to
yield increased optical absorption and photocurrent generation in the photoactive layer over a broad
range of visible wavelengths by inducing surface plasmons through careful control of metallic
nanoparticle’s properties.
With incident light, the surface charges of metallic nanoparticles interact with the electromagnetic field,
leading to an electric field enhancement that can then be coupled to the photoactive absorption region. It has
been extensively studied that surface plasmons can be tuned by changing the size, shape, particle material,
substrates and overcoating of the metal particles
Fabrication process
An organic salt of Ag was decomposed under controlled condition resulting in formation of Ag nanoparticles.
The nanoparticles were capped by carboxylic ligand
ITO
PEDOT:PSS
AgNP
ITO
PEDOT:PSS
P3HT:PCBM
P3HT:PCBM
Ca/Al
Ca/Al
The cell structure in this study
For the control experiment
Corresponds to a ~16% increase of the total optical
IPCE : Incident Photon to Current Efficiency
absorption of the devices in the spectral range of 350
Short circuit current increased from 6.2 mA/cm2
– 650 nm
to 7.0 mA/cm2
One very definite cell requirement for composite cell measurements is that total energy illuminating the
cells is not larger than the energy in the reference spectrum i.e. portions of the solar spectrum are not
used twice. Examination of the results in Table I shows that this requirement is met in principle but not
in detail for this data set.
The authors [4] recognise this limitation but suggest that, as the GaInP cell is the current
limiting cell, this overlap is not important. Even if correct, however, the overlap would
improve the voltage and fill-factor of the combination, at least marginally.
The corresponding current measured experimentally for the silicon cell in the split-spectrum
combination of Table I is 11.7 mA/cm2, immediately confirming a contribution from wavelengths
beyond 1100 nm. Correcting for this would result in about 10% relative reduction in performance
(0.5% absolute efficiency reduction). Correcting for the overlap in the 871–890 nm range would result
in a similar further reduction. Considering that the GaAs cell in the high-bandgap cell stack might not
be at full response over this range, as argued by the authors [4], it can be concluded that the two
regions of overlap inflate the absolute efficiency reported for the silicon cell and hence for the cell
combination by 0.5–1% absolute.