Light harvesting antenna complexes

Abstract

The invention disclosed concerns a simple ring-hub arrangement of interacting two-level systems using a theoretical quantum jump approach which mimics a biological light-harvesting antenna connected to a reaction center.

Claims

1. An element comprising a substrate comprising a substrate material and having a substrate surface having one or more substrate surface regions; and a multilayered structure comprising at least two nanoparticle layers, said multilayered structure being associated with at least one of the one or more substrate surface regions, each of said at least two nanoparticle layers comprising nanoparticles of a different type, a band gap of the substrate material being larger than a band gap of nanoparticles in a layer directly associated with the substrate, and the band gap of the substrate material being smaller than a band gap of nanoparticles in a top-most layer of said multilayered structure, and wherein each of said at least two nanoparticle layers is associated via one or more organic linker molecules to the substrate surface and/or nanoparticles of a neighboring layer, to cause charge or energy transfer between the at least two nanoparticle layers.

2. The element according to claim 1, wherein the multilayered structure comprises (a) a first nanoparticles layer, (b) the top-most layer, and (c) at least one additional layer of nanoparticles, being positioned between the first nanoparticles layer and the top-most layer, wherein the band gap of the nanoparticles of said at least one additional layer (c) being smaller than the band gap of the nanoparticles in the top-most layer (b) and larger than the band gap of the nanoparticle in the first layer (a).

3. The element according to claim 1, wherein the nanoparticles in any of the at least two nanoparticle layers of the multilayered structure are associated to each other or to the substrate via the one or more organic linker molecules.

4. The element according to claim 3, wherein the one or more organic linker molecules is selected to permit charge or energy transfer (up-conversion or down-conversion) between each two layers or a layer and the substrate.

5. The element according to claim 3, wherein the one or more organic linker molecules is bifunctional.

6. The element according to claim 1, wherein the nanoparticles in any of the at least two nanoparticle layers of the multilayered structure are composed of a material selected from a semiconductor and/or a metal.

7. The element according to claim 1, wherein the nanoparticles in any of the at least two nanoparticle layers of the multilayered structure comprise metallic material.

8. The element according to claim 1, wherein the nanoparticles in any of the at least two nanoparticle layers of the multilayered structure are doped with at least one atom or at least one ion.

9. The element according to claim 1, wherein the different type of the nanoparticles of the each of said at least two nanoparticle layers is selected from at least one of nanoparticle material, particle size, particle shape, particle structure, presence or absence of doping atoms (materials), selection of dopants, concentration of dopants, valance band offset, and particle band structure.

10. A device implementing the element according to claim 1.

11. The device according to claim 10, configured for converting light to electrical energy or vice versa.

12. The device according to claim 11, being a photovoltaic cell.

13. The element according to claim 1, wherein each of the at least two nanoparticle layers is associated directly or via the one or more organic linker molecules with the substrate surface and/or nanoparticles of a preceding and/or subsequent layer.

14. The element according to claim 1, wherein the charge or energy transfer between each two nanoparticle layers or a nanoparticle layer and the substrate enables light harvesting.

15. A light harvesting device being an element according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In order to understand the disclosure and to see how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

(2) FIG. 1 is a SEM micrograph of the InAs nanodot monolayer.

(3) FIG. 2 is a photoluminescence (PL) spectrum of InAs nanodots for different linker molecules measured at 10 K with 100 mW, 532 nm laser. The thin line is the PL spectra of the original solution of NP. The inset shows the integrated signal for two excitation wavelengths of 530 and 830 nm for different attaching molecules. The integrated signal was normalized for the smallest response at each wavelength.

(4) FIG. 3 presents, on the left, a schematic illustration of a transistor device; on the middle, absolute response of the device as a function of the source-drain current at 300 K; and on the right, the actual device. Inset: shows the nonlinear absolute response as a function of number of layers.

(5) FIG. 4 presents, on the left a scheme of the designed mask of the Si photo cell; on the right a picture of the PN photo cell used for measurements.

(6) FIG. 5 is an I-V curve of a solar cell with old and new contacts. The new contacts IV shown are ohmic for the 1 to 1V range, with resistance of 1 kOhm.

(7) FIG. 6 is the spectral response curve of a measured cell.

(8) FIG. 7 is a graph of the response to visible light of the same solar cell with NCs, before and after oxidizing the NCs.

(9) FIG. 8 is a normalized response graph of the Si detector to the visible and UV light.

(10) FIG. 9 is a transmission graph of a solar cell with and without 5 monolayers of NCs.

DETAILED DESCRIPTION OF EMBODIMENTS

(11) Antenna complexes of photosynthetic cyanobacteria (oxygen evolving prokaryotes) poses superior excitation transfer efficiency at room temperature. Recent studies showed that the exceptional energy transfer in certain antenna systems could be ascribed to coherent quantum properties. Photosynthetic antenna proteins have been studied that are isolated and dried on several substrates. Preliminary results show ordering of the proteins followed by a peak shift from the in vitro protein emission. It has been demonstrated by the inventors that during the drying process the proteins tend to arrange in super-molecular organization mimicking the native proteins. Such structures can serve as a nano-metric energy transmission lines, and may be used to couple light to nano devices.

(12) In order to build artificial molecules, quantum dots or any other nanoparticle grown by colloidal chemistry (referred to herein in general as nanocrystals, NCs) have been used to demonstrate a controlled growth of composition and size. These systems have been employed in conjunction with semiconducting polymers to create both light-emitting diodes and photovoltaic devices, utilizing the highly tunable level structure of NCs as well as the chemical process ability of the particles.

(13) Attaching NCs to a solar cell device via organic molecules, using self-assembly methods, makes the production of the system simple and flexible in terms of the materials (semiconductors, metals, ferroelectric) and accessible range of NC dimensions. In the approach implemented in the technology of the invention, the inventors introduce a novel nano toolbox enabling control over coupling and charge transfer between the NC and the substrate.

(14) Combining NCs, organic linkers, and a semiconductor solar cell, this tool box can be used to tune the response spectrum by changing the size or nature of the NCs and by controlling coupling. FIG. 1 presents a SEM scan of an InAs nano crystal monolayer attached to the GaAs substrate by organic molecules. The molecules can be selected according to their length and chemical bond strength, which influence the electron or hole conductance, as well as its molecular symmetry affecting the spin conductance.

(15) This combination of semiconductor NCs having various size-tunable properties, together with control over the binding molecules and the possibility of adding gold NCs creates an arsenal of nanotools that allow self-assembly of all its components into a supramolecular system of pre-designed optical as well as electronic properties.

(16) The multilayered systems are constructed by combining, e.g., semiconductor NCs with organic molecules as linkers. An excited electronic state of a NC donor unit will be prepared by photoexcitation. The charge transfer from photoexcited NC to either a second NC or to the semiconductor substrate was studied for different types of organic linker molecules and different types of nanoparticles.

(17) Measurements conducted have been able to determine the parameters that influence the exact charge, spin or exciton passing the constructed organic barrier. Understanding these coupling effects between the quantum world and the classical device is a key in the bottom-up/up-down approach to quantum device design. The optical measurements results, which demonstrate the changes in coupling using different organic molecules, are presented in FIG. 2.

(18) FIG. 2 presents an example of the means to study charge transfer and coupling control using organic molecules by using photoluminescence (PL) measurements. Nanoparticles were connected to a GaAs substrate using three types of molecules: HS(CH.sub.2).sub.2SH (EDT ethanedithiol), HS(CH.sub.2).sub.10SH (decanedithiol DT), and HSCH.sub.2--CH.sub.2SH (benzenedimethanethiol BDMT). The PL spectra of the InAs nanodots for different linker molecules were measured at 10 K with 100 mW, 532 nm laser. The thin line in FIG. 2 is the PL spectrum of the original solution with the nano crystals (NCs). At 530 nm, the GaAs substrate absorbed most of the laser power and a considerable portion of the charge reached the substrate surface. Therefore, the stronger the coupling was, the stronger the PL signals which have been observed. At only 830 nm the NCs adsorbed the laser power and an opposite effect was observed. The inset shows the integrated signal for two excitation wavelengths of 530 and 830 nm for different attaching molecules. The integrated signal was normalized to the smallest response at each wavelength.

(19) The charge and energy transfer efficiency using three layers of NCs is shown in FIG. 3 left. The sensors were prepared by standard photo lithography techniques and coupled to a FET device. FIG. 3 center shows the absolute response of the device as a function of the source-drain current at 300 K. The inset shows the nonlinear absolute response as a function of number of layers. It is clear that the response increases with the number of layers. By changing the coupling efficiency of each layer we achieved a non-linear response as a function of the number of layers.

(20) Together with the optical measurements both the charge and energy transfer could be measured. Charge transfer activates the device response and energy transfer can be measured optically. Exploiting both tools together was essential to probe the properties of the suggested complex structure.
Solar Cells
Properties of Si Solar Cells

(21) The inventors have used a Si PN solar cell and compared the response of the solar cell with and without the nano crystals (NCs) layers. For this propose new n type Si wafers were obtained. All wafers were implanted in core systems creating a p-doped region above the n-type layer. After the implantation the solar cells were realized using standard photolithographic techniques.

(22) FIG. 4 left presents the mask used to fabricate the solar cells. An optical image of the solar cell is presented in the right picture of FIG. 4.

(23) For a full solar cell, optimization of the load was necessary in order to achieve maximum efficiency. In this case contacts with lower resistance were realized. Ohmic contacts with 1K ohm resistance (FIG. 5) were achieved.

(24) FIG. 6 shows the spectral response of a fabricated solar cell. At the UV region the response of the cell was less than 1% of the total response. Comparing the total response of a detector before and after the NCs adsorption, it was possible to measure a greater improvement in the response. This improvement was assumed to originate mainly from the short wavelength increase in efficiency.

(25) In FIG. 7 a comparison between the response of the same cell before and after oxidation of the NCs is demonstrated. To compare the effect of oxidation on the exact same cell, the solar cell with the NCs was deliberately exposed to NCs oxidation process a glove box. It was possible to observe that the layers adsorbed on a solar cell according to the present invention were immune to short time oxidation. Using CdS NCs the response of the device was not changed over a week of measurements.

(26) Using the NCs layer to convert the UV light to the visible, an improvement was achieved in the solar cell performance. The total response of the UV light absorption of the solar cell with NCs layers was around 5% of the visible response (FIG. 8). Without the NCs the response of the UV was around less than half.

(27) Improvement of the Si Cell by 5 Monolayer Adsorption

(28) Comparing the total response of the detector before and after adsorption of 5 monolayers, it was possible to measure about a greater improvement. This improvement was attributed to the short wavelength increase in efficiency. Comparing the transmission in the UV through a transparent film with and without the layers, enhanced emission was observed for the layered structure around 550 nm, as shown in FIG. 9.

(29) Improvement of Si Solar Cell by Using Doped NCs in the UV and IR Regions

(30) In order to increase the cells efficiency using the infrared spectrum, Ag doped ZnO nano crystals that show IR adsorption were used. Using the 5 ZnO NCs layers that converted UV light to the visible, the total response of the UV light absorption of the solar cell with NCs layers was around 8% of the visible response. Without the NCs, the response of the UV was less then one forth of the absorption.