Method of manufacture for a partially-sprayed layer organic solar photovoltaic cell

Abstract

The fabrication and characterization of large scale inverted organic solar array fabricated using all-spray process is disclosed. Solar illumination has been demonstrated to improve transparent solar photovoltaic devices. The technology using SAM has potential to revolute current silicon-based photovoltaic technology by providing a complete solution processable manufacturing process. The semi-transparent property of the solar module allows for applications on windows and windshields. The inventive modules are more efficient than silicon solar cells in artificial light environments. This significantly expands their use in indoor applications. Additionally, these modules can be integrated into soft fabric substances such as tents, military back-packs or combat uniforms, providing a highly portable renewable power supply for deployed military forces.

Claims

1. A method of manufacturing an organic solar photovoltaic cell, the method comprising: patterning ITO onto a substrate; applying a patterned, non-oxidized Self Assembled Molecule layer onto the patterned ITO, wherein the Self Assembled Molecule layer comprises N-propyl trimethoxysilane or aminopropyl triethoxysilane and wherein the layer of Self Assembled Molecule layer comprises no more than three single molecule layers, each single molecule layer having a thickness of less than or equal to about 2 nm such that the Self Assembled Molecule layer has an overall thickness of less than or equal to about 6 nm; annealing Self Assembled Molecule layer inside a glovebox; spraying an active layer of poly-3-hexylthiophene (P3HT) and (6,6)-phenyl C.sub.61 butyric acid methylester (PCBM) on the Self Assembled Molecule layer, wherein the active layer comprises a plurality of multiple light spray layers, each light spray layer comprising between about 600 μL and 900 μL of poly-3-hexylthiophene and (6,6)-phenyl C.sub.61 butyric acid methylester such that an overall thickness of the active layer is between about 130 nm to about 200 nm to form a solar photovoltaic cell; drying the solar photovoltaic cell in an antechamber under vacuum for at least 12 hours; spraying a layer comprising poly (3,4) ethylenedioxythiophene:poly-styrenesulfonate and 5 vol. % of dimethylsulfoxide on the active layer, wherein the layer comprising poly (3,4) ethylenedioxythiophene:poly-styrenesulfonate and 5 vol. % of dimethylsulfoxide comprises a plurality of individual sprayed-on layers such that the final thickness of the poly (3,4) ethylenedioxythiophene:poly-styrenesulfonate and 5 vol. % of dimethylsulfoxide layer is between about 500 nm and about 700 nm, wherein the poly (3,4) ethylenedioxythiophene:poly-styrenesulfonate and 5 vol. % of dimethylsulfoxide form at least one positive contact; disposing silver paint on the at least one positive contact; placing the solar photovoltaic cell into high vacuum for 1 h; annealing the solar photovoltaic cell; and encapsulating the solar photovoltaic cell with a UV-cured epoxy to form an organic solar photovoltaic cell.

2. The method of claim 1, wherein patterning ITO onto a substrate further comprises: obtaining an ITO-coated substrate; patterning the ITO-coated substrate using a photolithography pattern; etching the ITO-coated substrate; and cleaning the etched ITO-coated substrate.

3. The method of claim 2, wherein patterning the ITO-coated substrate using a photolithography pattern further comprises, spraying the photolithography pattern onto the ITO-coated substrate using a custom made spray mask.

4. The method of claim 2, wherein etching the ITO-coated substrate further comprises, etching the ITO-coated substrate using a mixed solution of HCl and HNO.sub.3.

5. The method of claim 2, wherein cleaning the etched ITO-coated substrate further comprises, cleaning the ITO-coated substrate by sonification in trichloroethylene, acetone, and isopropanol.

6. The method of claim 5, cleaning the ITO-coated substrate further comprises; cleaning the ITO-coated substrate at 50° C. for 20 min in trichloroethylene; cleaning the ITO-coated substrate at 50° C. for 2.0 min in acetone; cleaning the ITO-coated substrate at 50° C. for 2.0 min in isopropanol; and drying the ITO-coated substrate with N.sub.2.

7. The method of claim 1, wherein the active layer is poly-3-hexylthiophene (P3HT) and (6,6)-phenyl C.sub.61 butyric acid methylester (PCBM) in a weight ratio of 1:1 in dichlorobenzene.

8. The method of claim 7, further comprising, stirring the active layer on a hotplate for 48 h at 60° C. prior to spraying the active layer on the Self Assembled Molecule layer.

9. The method of claim 1, wherein spraying the layer comprising poly (3,4) ethylenedioxythiophene:poly-styrenesulfonate and 5 vol. % of dimethylsulfoxide on the active layer further comprises, prior to spraying the layer comprising poly (3,4) ethylenedioxythiophene:poly-styrenesulfonate and 5 vol. % of dimethylsulfoxide on the active layer: diluting the poly (3,4) ethylenedioxythiophene:poly-styrenesulfonate; filtering the diluted poly (3,4) ethylenedioxythiophene:poly-styrenesulfonate through a 0.45 μm filter; and mixing the dimethylsulfoxide into the diluted poly (3,4) ethylenedioxythiophene:poly-styrenesulfonate.

10. The method of claim 1, wherein the vacuum is 10.sup.−6 Torr.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For a fuller understanding of the invention, reference should be made to the following detailed description, taken in connection with the accompanying drawings, in which:

(2) FIG. 1 is a diagram showing a perspective view of the novel inverted OPV cells containing sprayed-on layers.

(3) FIG. 2 is a diagram showing the novel organic photovoltaic cell as it receives photons having energy hv.

(4) FIG. 3 is a graph showing current-voltage (I-V) of an inverted array using SAM under continuous AM1.5 solar illumination measured at different time points.

(5) FIG. 4 is a diagram of the device architecture showing a top view of the of an inverted array.

(6) FIG. 5 is a diagram showing the cross sectional view of the device architecture of an inverted solar array showing series connection.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

(7) The present invention for the fabricatation of a see-through organic solar array via layer-by-layer (LBL) spray may be understood more readily by reference to the following detailed description of the preferred embodiments of the invention and the Examples included herein. However, before the present compounds, compositions, and methods are disclosed and described, it is to be understood that this invention is not limited to specific compounds, specific conditions, or specific methods, etc., unless stated as such. Thus, the invention may vary, and the numerous modifications and variations therein will be apparent to those skilled in the art. It is also to be understood that the terminology used herein is for the purpose of describing specific embodiments only and is not intended to be limiting.

(8) As used herein, “about” means approximately or nearly and in the context of a numerical value or range set forth means ±15% of the numerical.

(9) As used herein, “substantially” means largely if not wholly that which is specified but so close that the difference is insignificant.

(10) All masks described herein for spray were custom made by Towne Technologies, Inc.

EXAMPLE

(11) The indium tin oxide (ITO) is patterend onto a glass substrate using a positive photo resist, such as Shipley 1813, spin coated at 4500 rpm and soft baked on a hotplate for 3 minutes at 90° C. The substrate is then exposed to a UV-lamp for 1.4 seconds in a constant intensity mode set to 25 watts. The structure was developed for about 2.5 minutes using Shipley MF319 and rinsed with water. The substrate was then hard-baked, at 145° C. for 4 minutes and any excess photoresist cleaned off with acetone and cotton. After cleaning, the substrate was etched from about 5-11 minutes with a solution of 20% HCl-7% HNO.sub.3 on a hotplate at 100° C. The etched substrate was then cleaned by hand using acetone followed by isopropanol and UV-ozone cleaned for at least 15 minutes.

(12) The Self-Assembled Monolayer (SAM) layer was formed on top of the patterned ITO layer. A solution of N-propyl trimethoxysilane (3 mM) in ethanol was prepared and stirred for 10 minutes at room temperature. Once the SAM solution was ready, the ITO substrate was placed in the prepared SAM solution and soaked for 36-48 hours inside an N.sub.2 glovebox at room temperature. The SAM solution provides a single-layer thickness of about, or less than, 2 nm. The substrate was then rinsed with ethanol, followed by a toluene wash and an isopropanol wash, each performed for 10 minutes.

(13) The active layer solution was prepared by mixing separate solutions of P3HT (high molecular weight) and PCBM (C.sub.60) in dichlorobenzene at 20 mg/mL and stirred on a hotplate for 24 hours at 60° C. These two separate solutions were then mixed together at a 1:1 ratio and stirred for 24 hours at 60° C., producing a final solution of 10 mg/mL. The active coating was then spray coated onto the SAM layer using an airbrush with N.sub.2 set to 30 psi. The airbrush was set at about 7-10 cm away from the substrate and multiple light layers of active layer were sprayed. For each spray, the solution used was about 600-900 μL.

(14) A final thick continuous coat of active layer was applied onto the multiple thin layers to complete the active layer coating, forming a thickness of between about 130 nm to about 200 nm. After drying, excess active layer solution was wiped off of the substrate using dichlorobenzene (DCB)-wetted cotton followed by isopropanol-wetted cotton. The substrate was then left to dry in the antichamber, under vacuum for at least 8-12 hours.

(15) A kovar shadow mask was aligned in position with the substrate and held in place by placing a magnet underneath the substrate. The series connection locations were wiped using a wooden dowel to expose the cathode for later electrical connection.

(16) The modified PEDOT (m-PED) layer was prepared by adding dimethylsulfoxide at a concentration of 5% by volume to a solution of filtered PEDOT:PSS. The solution was then stirred at room temperature followed by 1 h of sonification. The m-PED coating was prepared by placing a substrate/mask on a hotplate (90° C.). The m-PED layer was spray coated using nitrogen (N.sub.2) as the carrier gas, set to 30 psi, with the airbruch positioned about 7-10 cm from the substrate. Multiple light layers were applied until the final thickness of about 500 nm to about 700 nm was reached. The substrate was then removed from the hotplate and the mask removed. Care was taken to avoid removing the mPED with the mask. The substrate was placed into high vacuum treatment (10.sup.−6 Torr) for 1 h, followed by a substrate annealing at 120-160° C. for 10 min.

(17) The substrate was encapsulated using a silver paint applied to the device contacts, which were then allowed to dry. The encapsulation glass was notched and cleaned by hand using acetone and isopropanol, followed by UV-ozone cleaning. UV-cure epoxy encapsulant (EPO-TEK OG142-12; Epoxy Technology, Inc., Hiflerica Mass.) was applied to the edge of the encapsulation glass, and the glass is placed into the glovebox for at least 15 min, with UV exposure. The device was then flipped upside down, and the epoxy applied on top of the encapsulation glass. The device was finally exposed to 15 min of UV to cure the encapsulant epoxy.

EXAMPLE 2

(18) Inverted organic photovoltaic cell 1, seen dissected in FIG. 1, was created using the method described in Example 1. Inverted photovoltaic cell 1 was composed of different layers of active materials and terminals (anode and cathode) built onto substrate 5. Anode 10, comprised of ITO in the present example, was sprayed onto substrate 5 forming a ‘’ pattern extending from a first set of edges of substrate 5. SAM layer 40 covers anode 10, except for the outermost edges, as seen in FIG. 2. The components of the SAM layer were chosen to provide a gradient for charges crossing the interface, approximating a conventional p-n junction with organic semiconductors, thereby providing an increased efficiency of heterojunctions. Active layer 30 is disposed directly on top of interfacial buffer layer 40, and was prepared using poly(3-hexylthiophene) and 6,6-phenyl C61 butyric acid methyl ester. Anode 20 was disposed on the active layer in a pattern, similar to the cathode, but perpendicular to the cathode. Exemplary anode materials include PEDOT:PSS doped with dimethylsulfoxide. The fully encapsulated 4 μm×4 μm array was found to possess over 30% transparency.

(19) The device was analyzed by exposing the cell to continuous radiation, as seen in FIG. 2. The photovoltaic cell was exposed to continuous illumination from a Newport 1.6 KW solar simulator under AM1.5 irradiance of 100 mW/cm2. Current-voltage (I-V) results from continuous AM1.5 solar illumination from the UV lamp showed that the inverted array using SAM under generated a voltage of V.sub.oc=1.2 V, current of I.sub.sc=3.2 mA, FF=0.23, and a power conversion efficiency (PCE) of 0.3% for the 3.sup.rd measurement, as seen in FIG. 3.

EXAMPLE 3

(20) Solar illumination has been demonstrated to improve solar array efficiency up to 250%. Device efficiency of 1.80% was observed with the array under AM1.5 irradiance. Data have shown that the performance enhancement under illumination only happens with sprayed devices, not devices made by spin coating (See, Lewis, et al., PCT/US11/54290). This means that solar cells made using the present spray-on technique perform better under sunlight, which is beneficial for solar energy application.

(21) A solar array was prepared by forming 50 individual inverted cells as described above, each with an active area of 60 mm.sup.2. The array was configured with 10 cells in series in one row to increase the voltage, and five rows in parallel connection to increase the current. The neighboring cells were connected using the organic layer configuration, seen in FIG. 4 and in cross section in FIG. 5.

(22) In the preceding specification, all documents, acts, or information disclosed does not constitute an admission that the document, act, or information of any combination thereof was publicly available, known to the public, part of the general knowledge in the art, or was known to be relevant to solve any problem at the time of priority.

(23) The disclosures of all publications cited above are expressly incorporated herein by reference, each in its entirety, to the same extent as if each were incorporated by reference individually.

(24) While there has been described and illustrated specific embodiments of an organic photovoltaic cell, it will be apparent to those skilled in the art that variations and modifications are possible without deviating from the broad spirit and principle of the present invention. It is intended that all matters contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.