previous work on cvd-grown sinws single sinw nature| vol 449| 18 october 20070 removed from the...

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Previous work on CVD-grown SiNWs Single SiNW NATURE| Vol 449| 18 October 20070 •Removed from the growth substrate and laid on a foreign substrate •Contacts are formed by optical or e-beam lithography As-grown arrays of SiNWs APL 91, 233117 2007 •wafer-scale active areas, consists in directly integrating an as-grown array of vertically aligned SiNWs •Efficiency is about 0.1%

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Previous work on CVD-grown SiNWsSingle SiNW

NATURE| Vol 449| 18 October 20070

•Removed from the growth substrate and

laid on a foreign substrate

•Contacts are formed by optical or e-beam

lithography

As-grown arrays of SiNWs

APL 91, 233117 2007

•wafer-scale active areas, consists in directly integrating

an as-grown array of vertically aligned SiNWs

•Efficiency is about 0.1%

(100)-oriented

•n-type SiNWs fabricated by CVD

As-grown

D ~ 40 nm

After SOP coated Final structure

The novelty of this study is planarization of the SiNW array

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 processAn 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

P3HT:PCBM

Ca/Al

ITO

PEDOT:PSS

P3HT:PCBM

Ca/Al

The cell structure in this study For the control experiment

Corresponds to a ~16% increase of the total optical

absorption of the devices in the spectral range of 350

– 650 nm

IPCE : Incident Photon to Current Efficiency

Short circuit current increased from 6.2 mA/cm2

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.