Previous work on CVD-grown SiNWs

1. As-grown arrays of SiNWs Previous work on CVD-grown SiNWs SingleSiNW 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 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%

2. The novelty of this study is planarization of the SiNW array (100)-oriented • n-type SiNWs fabricated by CVD As-grown D ~ 40 nm Final structure After SOP coated

3. 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

4. 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’sproperties. 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

5. 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 ITO PEDOT:PSS PEDOT:PSS AgNP The cell structure in this study For the control experiment P3HT:PCBM P3HT:PCBM Ca/Al Ca/Al

6. 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

9. 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.

10. 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-bandgapcell 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.