Bio-inspired Photovoltaic Cells

C.M. Fortmann1,*, M. Sadoqi1,2, S. Kumar3

1 Physics Department, St John’s University, NY, USA

2 department of Pharmaceutical Sciences, St John’s University, NY, USA

3 Mechanical Engineering Department, NYU, NY, USA

* fortmanc@stjohns.edu

 

1) Context / Study motivation

A study of natural plant photon harvesting leads to new strategies for molecular absorber-based photovoltaic cells. The study focused on the natural processes related to photosynthesis that are not well defined. Namely, the study focused on the nature and consequences of the initial photo-absorption mechanism and the properties of the resultant exciton. Surprisingly, experiments described here did not confirm the well-accepted Forster exciton model wherein photons induce energy “storing” electron resonance.

Rather hydrogen-like excitons similar to those found in semiconductors better fit he data. Further experiments are currently being conducted. Nonetheless gained insights establish criteria for a new type of solar cell based on hydrogen-like exciton photo-absorption in chlorophylls and related synthetic molecules. Wherein charge separation is by neutral exciton drift in a permittivity gradient.

The molecular-absorber photovoltaic cell advantages include: in-situ spectral tuning and replenishment of absorber molecules as well as the use of ultra low cost absorber molecules derived natural plant chlorophylls and chromophores.

2) Analysis of Natural Photo-Absorption

The optical absorption of natural chlorophyll (from spinach) and sodium copper chlorophyllin (a synthetic molecule similar to chlorophyll used by the food industry for color and relative stability) was measured in a variety of media of varying refractive index. Since the wavelength of visible light is much larger than that of the molecules studied and since the wavelength of light is predicated on the refractive index of the media, light wavelength was systematically varied. The resonant absorption model was compared and contrasted with a hydrogen-like exciton model. Further experiments probed the possibility of a photo-induced magnetic moment related to the exciton orbit. Prototype photovoltaic structures were designed and tested.

3) Photo-Absorption in Plant Chlorophylls

The principal absorption peak at did not shift with media however the magnitude of the absorption was strongly dependent on the media as seen in Figures 1 as well as Tables I. However, the absorption magnitude was not systematically related to the media refractive index.

      The results for chlorophyll are summarized in Tables I. It is evident that no systemic relation between refractive index and absorption magnitude or peak position is discernable. The lack of systemic change because the well-accepted Forster-resonant absorption model necessarily is dependent on antenna aperture that is wavelength dependent:

      The hydrogen-like exciton has no implicit refractive index dependence however the full manuscript will show that it does have permittivity dependence that is consistent with the measured changes.

      Exciton absorption opens a door to engineering solar cells employing exciton drift to transport and separate charge. Since excitons are neutral drift is not possible in an electric field. However, it is shown (in the full paper) that excitons experience drift in a permittivity gradient towards increasing permittivity due to interaction with the molecular environment. The electric field energy is reduced by increased media permittivity. Among the intriguing implications are the possibilities that plants have evolved to exploit these mechanisms to transport energy away from delicate membrane structures having low permittivity to high dielectric regions in the photosynthesis center where photochemistry occurs.

      In-turn these concepts provide tantalizing design opportunities for: novel, ultra low cost, sustainable, and in-situ spectral tunable solar cells. Solar cell design will be discussed in the full paper.

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BIOGRAPHIE:

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Mostafa Sadoqi is currently Chair and Professor of Physics at St John’s University and he holds a join appointment as a Professor of the pharmaceutical Sciences. He earned his PhD in Physics (Nanotechnology), and two Masters of Science in Physics and Electrical Engineering from Polytechnic Institute of New York University. He was invited scientists at Science and Technology Agency Fellow in Japan.

His research interests are in modeling of propagation of light in soft and hard tissue, developing multifunctional biophotonic nanosystems combine with lasers that can be used to detect, monitor and eradicate tumors in breast and brain tissues, and fabricating polymeric nanoparticles for drug delivery and imaging within tissue. Also, he has interests in optical and thermal analysis of biological materials, and optical and chemical sensors. He is currently working on synthesis and characterization of nanomaterials and related applications for photovoltaic and photonic devices. In addition, he has an interest on green solar energy applications.

Dr Sadoqi has published more than 120 research papers and presentations. Also, book chapters and holds patent.

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