The necessary length of carbon nanotubes required to optimize solar cells

Chemistry Central Journal, Oct 2007

Background In recent years scientists have been trying both to increase the efficiency of solar cells, whilst at the same time reducing dimensions and costs. Increases in efficiency have been brought about by implanting carbon nanotubes onto the surface of solar cells in order to reduce the reflection of sunrays, as well as through the insertion of polymeric arrays into the intrinsic layer for charge separation. Results The experimental results show power rising linearly for intrinsic layer thicknesses between 0–50 nm. Wider thicknesses increase the possibility of recombination of electrons and holes, leading to perturbation of the linear behaviour of output power. This effect is studied and formulated as a function of thickness. Recognition of the critical intrinsic layer thickness can permit one to determine the length of carbon nanotube necessary for optimizing solar cells. Conclusion In this study the behaviour of output power as a function of intrinsic layer thicknesses has been described physically and also simulated. In addition, the implantation of carbon nanotubes into the intrinsic layer and the necessary nanotube length required to optimize solar cells have been suggested.

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The necessary length of carbon nanotubes required to optimize solar cells

Majid Vaezzadeh 0 Mohammad Reza Saeedi 0 Tirdad Barghi 0 Mohammad Reza Sadeghi 0 0 Address: K.N. Toosi University, Department of Physics , 41, Shahid Kavian St., 15418-49611 Tehran, Iran Background: In recent years scientists have been trying both to increase the efficiency of solar cells, whilst at the same time reducing dimensions and costs. Increases in efficiency have been brought about by implanting carbon nanotubes onto the surface of solar cells in order to reduce the reflection of sunrays, as well as through the insertion of polymeric arrays into the intrinsic layer for charge separation. Results: The experimental results show power rising linearly for intrinsic layer thicknesses between 0-50 nm. Wider thicknesses increase the possibility of recombination of electrons and holes, leading to perturbation of the linear behaviour of output power. This effect is studied and formulated as a function of thickness. Recognition of the critical intrinsic layer thickness can permit one to determine the length of carbon nanotube necessary for optimizing solar cells. Conclusion: In this study the behaviour of output power as a function of intrinsic layer thicknesses has been described physically and also simulated. In addition, the implantation of carbon nanotubes into the intrinsic layer and the necessary nanotube length required to optimize solar cells have been suggested. - Background Developing inexpensive and renewable energy sources is one of the most important scientific and technological challenges of our time. Solar energy is an inexhaustible energy source that can be harnessed to meet our growing future energy needs. However, traditional photovoltaic (solar-to-electric conversion) technology is too expensive to be the suitable alternative for fossil fuels or even other competing renewable energy sources. A significant leap in the scientific and technological progress of renewable energy sources will be required to displace proven, but unsustainable energy production methods. Nanotechnology is driving new interesting developments in photovoltaic technology. Advances in organic synthesis and characterization techniques allow us to coax a photocurrent from organic, 'soft' molecules in a process that mimics photosynthesis in plants, thus potentially opening up the way to cheap, ubiquitous solar cells. Power production resulting in zero greenhouse gas emissions is economically and environmentally desirable. Direct photovoltaic conversion of sunlight into electricity is therefore the highly attractive alternative to unsustainable energy sources such as fossil fuels. Although silicon solar cells have gained a considerable market share and commercial success, high production and up-front installation costs still limit their commercial viability. In this study, we explore the use of low-cost advanced materials for photovoltaic energy production and the mechanism of photovoltaic action in a new class of solar cell, that is, the heterojunction photovoltaic. These are constructed from a thin film of cheap composite material, a mixture of carbon nanotubes and conductive polymer [1]. Results We now aim to address the issues that determine the thickness of the absorber (or "intrinsic") layer. Figure 1 illustrates a computational calculation that shows how the output power of an a-Si-based pin cell varies with intrinsic layer thickness. The curves differ in the specified cFCeiogllmuarpseuat1efurnccatlicounlaotifointorifntshice lpayoewretrhiocuktnpeusts from a pin solar Computer calculation of the power output from a pin solar cell as a function of intrinsic layer thickness. The differing curves indicate results for monochromatic illumination with absorption coefficients from 5000/cm to 100 000/cm; for typical a-Si: H, this range corresponds to a photon energy range from 1.8 to 2.5 eV. Solid symbols indicate illumination through the p-layer and open symbols indicate illumination through the n-layer. Incident photon flux = 2 1017/cm2s; no back reflector. The data are obtained from real experiments, with the curves calculated using methods outlined in the references [3-8]. absorption coefficients for a monochromatic illumination using varying photon energies. All curves were calculated for the same photon flux. Such illumination conditions might be achieved by experiment using a laser whose photon energy can be tuned from 1.8 to 2.3 eV, however the presence of sunlight, of course, presents a much more complex situation. We will first discuss the results for illumination through the p-layer (solid symbols in the figure). For intrinsic layers that are sufficiently thin, the power is proportional to the number of photons absorbed (i.e. to the product of the thickness, d and the absorption coefficient, ). Within this limit the fill factors have nearly ideal values around 0.8. As the thickness of the cell increases, the power saturates. In figure 1 the first plot ( = 100 000/cm corresponding photon energy of about (...truncated)


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Majid Vaezzadeh, Mohammad Reza Saeedi, Tirdad Barghi. The necessary length of carbon nanotubes required to optimize solar cells, Chemistry Central Journal, 2007, pp. 22, Volume 1, Issue 1, DOI: 10.1186/1752-153X-1-22