Organic solar cells are promising for technological applications, as they are lightweight and mechanically robust. This study presents flexible organic solar cells that are less than 2 μm thick, have very low specific weight and maintain their photovoltaic performance under repeated mechanical deformation.

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Ultrathin and lightweight organic solar cells with high flexibility

Flexible CIGS, CdTe and a-Si:H based thin film solar cells: A review

An amorphous silicon solar cell on a periodic nanocone back reflector with a high 9.7% initial conversion efficiency is presented. The optimized back-reflector morphology provides powerful light trapping and enables excellent electrical cell performance. Up-scaling to industrial production of large-area modules should be possible using nanoimprint lithography.

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High‐Efficiency Amorphous Silicon Solar Cell on a Periodic Nanocone Back Reflector

We investigate amorphous silicon (a-Si:H) thin film solar cells in the n-i-p or substrate configuration that allows the use of nontransparent and flexible substrates such as metal or plastic foils such as polyethylene- naphtalate (PEN). A substrate texture is used to scatter the light at each interface, which increases the light trapping in the active layer. In the first part, we investigate the relationship between the substrate morphology and the short circuit current, which can be increased by 20% compared to the case of flat substrate. In the second part, we investigate cell designs that avoid open-circuit voltage (Voc) and fill factor (FF) losses that are often observed on textured substrates. We introduce an amorphous silicon carbide n -layer (n-SiC), a buffer layer at the n/i interface, and show that the new cell design yields high Voc and FF on both flat and textured substrates. Furthermore, we investigate the relation between voids or nanocrack formations in the intrinsic layer and the textured substrate. It reveals that the initial growth of the amorphous layer is affected by the doped layer which itself is influenced by the textured substrate. Finally, the beneficial effect of our optical and electrical findings is used to fabricate a-Si:H solar cell on PEN substrate with an initial efficiency of 8.8% for an i -layer thickness of 270 nm. © 2008 American Institute of Physics.

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Optimization of amorphous silicon thin film solar cells for flexible photovoltaics

SUMMARY
It is well known that current fossil fuel usage is unsustainable and associated with greenhouse gas production. The amount of the world's primary energy supply provided by renewable energy technologies is urgently required. Therefore, the relevant technologies such as hydrogen fuel, solar cell, biotechnology based on nanotechnology, and the relevant patents for exploiting the future energy for the friendly environment are reviewed. At the same time, it is pointed out that the significantly feasible world's eco-energy for the foreseeable future should not only be realized, but also methods for using the current energy and their by-products more efficiently should be found correspondingly, alongside technologies that will ensure minimal environmental impact. Copyright © 2011 John Wiley & Sons, Ltd.

Green nanotechnology of trends in future energy: a review

Fabrication of thin film silicon solar cells on plastic substrate by very high frequency PECVD

Transparent conducting oxide layers for thin film silicon solar cells

The aim of this research is to fabricate high efficiency a-Si/μc-Si tandem solar cell modules on flexible (polymer) superstrates using the Helianthos concept. As a first step we began by depositing the top cell which contains an amorphous silicon (a-Si:H) i-layer of ∼350 nm made by VHF PECVD at 50 MHz in a high vacuum multichamber system called ASTER, with hydrogen to silane gas flow ratio of 1:1. Such amorphous cells on-foil showed an initial active area (0.912 cm2) efficiency of 7.69% (Voc = 0.834 V, FF = 0.71). These cells were light soaked with white light at a controlled temperature of 50 °C. The efficiency degradation was predominantly due to degradation of FF that amounted to only 11% after 1000 h of light soaking. The cell-on-foil data prove that thin film silicon modules of high stability on cheap plastics can be made at a reasonable efficiency within 30 min of deposition time. A minimodule of 8 × 7.5 cm2 area (consisting of 8 cells interconnected in series) with the same single junction a-Si:H p–i–n structure had an initial efficiency of 6.7% (Voc = 6.32 V, FF = 0.65).

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Thin film silicon modules on plastic superstrates

In order to increase industrial viability and to find niche markets, high deposition rate and low temperature depositions compared to standard deposition conditions are two recent trends in research areas concerning thin film silicon. In situ diagnostic tools to monitor gas phase conditions are useful in quick optimization processes of deposition parameters without going into time consuming material characterizations. Optical emission spectroscopy is an efficient technique to monitor/predict growth rate and phase of the material (amorphous or nanocrystalline). However, at high growth rate conditions which are generally achieved at high chamber pressures (p), the simple correlation breaks down. We see that at high pressure condition a higher Hα/Si* is needed for the onset of crystallinity than that is found at lower pressure conditions. Additional methods such as estimating the silane depletion from the experiment and the flux ratio of atomic hydrogen to deposited silicon atoms from simulations can be used for fine-tuning the amorphous to nanocrystalline transition regime. On the other hand, intensity of Si* line loses its character as a monitoring tool for deposition rate. Moreover, the plasma changes its character when the pressure is varied, even when the pd product is kept constant. In situ diagnosis of the ion energy distribution function by a retarding field ion energy analyzer has thrown new lights on the role of hydrogen dilution for depositions at low substrate temperature conditions, namely to compensate the loss in ion energy due to lower gas temperature.

/pdf/gas-phase-considerations-for-the-growth-of-device-quality-2q6wuvb6wf.pdf

Gas phase considerations for the growth of device quality nanocrystalline silicon at high rate

Micromorph silicon tandem solar cells on Asahi U-type SnO 2 :F coated glass substrates have been fabricated by very high frequency plasma enhanced chemical vapour deposition (VHF-PECVD) in an ultra high vacuum multichamber system called ASTER. The hydrogenated microcrystalline silicon (μc-Si:H) intrinsic layer (i-layer) was deposited using a capacitively coupled reactor with a shower head cathode at high pressure depletion (HPD) conditions. We made bottom cell current limited tandem cells on Asahi U-type substrates, and they showed an initial efficiency of 10.2% ( V oc  = 1.34 V, FF = 0.69). To develop the fabrication process of such tandem cells as flexible solar cells, we began as a first step the deposition of hydrogenated amorphous silicon (a-Si:H) p-i-n single junction cells on aluminium foil (provide by Helianthos b.v.) which was then transferred to plastic substrate at Helianthos b.v. Such a-Si:H cells showed an initial active area efficiency of 7.69% ( V oc  = 0.834 V, FF = 0.70) and FF degraded by only 11% after 1000 h of light soaking, showing a high stability of these single junction cells. A minimodule (consisting of 8 cells) on foil delivered an initial aperture area efficiency of 6.7% ( V oc  = 6.32 V, FF = 0.65).

Y. Liu

Papers

Fabrication of thin film silicon solar cells on plastic substrate by very high frequency PECVD

Transparent conducting oxide layers for thin film silicon solar cells

Thin film silicon modules on plastic superstrates

Gas phase considerations for the growth of device quality nanocrystalline silicon at high rate

Development of micromorph tandem solar cells on foil deposited by VHF-PECVD