Update on Spray-on Solar PV

In a previous post I reported on a number of patent applications related to transparent solar panel technology that could be manufactured by a spray-on process.  This technology was being developed by Prof Xiaomei Jiang under a research agreement with New Energy Technologies Inc.  This company has now changed its name to Solar Window Technologies Inc. and there is much less evidence of the spray-on approach in their technical information suggesting that they are less confident that spraying will be a viable manufacturing route.

The patent applications have been going through examination and until quite recently there had been no granted patents emerging with the spray-on process as the key manufacturing method.  However, on 4 Aug 2015 the US20130255757 application was granted as US9099605 and as far as I am aware becomes the first granted patent with a spray-on process for PV panels.

Phil’s Comments:

I noticed that the first claim had to be modified before the examiner would allow it.  It has been somewhat narrowed in scope to include a 48h at 60°C heating step for the P3HT and PCBM before spraying multiple layers to a final thickness of between 200 and 300nm.  It was necessary to include this to avoid prior art found in the scientific literature which indicated a spray method but the layer needed to be thicker than 1.2 micron.  Other prior art also made mention of the heating requirements but failed to specify the layer thickness. Similarly, where layer thickness was specified in the prior art, it did not teach the heating steps were essential.

 

Spray on Solar PV

New Energy Technologies Inc. have been promoting a new spray-on, see through solar PV coating which can be applied to glass windows.  Earlier this year they were indicating that around 20 new patent filings have been submitted for their proprietary SolarWindow™ technology.  Last year I reported on one of the early patent filings and the article can be viewed here.  Dr Xiaomei Jiang has been leading this effort with New Energy Technologies under a Sponsored Research Agreement at the University of South Florida (USF).

Two more patent applications have emerged this month from Dr Jiang at USF and they continue to reveal further details of the spray on techniques and solar PV architecture.

US20130255757: ORGANIC PHOTOVOLTAIC ARRAY AND METHOD OF MANUFACTURE

Publication date: 03/10/2013

Inventor(s): JIANG XIAOMEI JANE [US]; LEWIS JASON ERIK [US]

Abstract

The fabrication and characterization of large scale inverted organic solar array fabricated using all-spray process is disclosed, consisting of four layers; ITO-Cs2CO3-(P3HT:PCBM)-modified PEDPT:PSS, on a substrate. With PEDPT:PSS as the anode, the encapsulated solar array shows more than 30% transmission in the visible to near IR range. Optimization by thermal annealing was performed based on single-cell or multiple-cell arrays. Solar illumination has been demonstrated to improve solar array efficiency up to 250% with device efficiency of 1.80% under AM1.5 irradiance. The performance enhancement under illumination occurs only with sprayed devices, indicating device enhancement under sunlight, which is beneficial for solar energy applications. The semi-transparent property of the solar module allows for applications on windows and windshields, indoor applications, and soft fabric substances such as tents, military back-packs or combat uniforms, providing a highly portable renewable power supply for deployed military forces.

US20130263916: ALL SPRAY SEE-THROUGH ORGANIC SOLAR ARRAY WITH ENCAPSULATION

Publication date: 10/10/2013

Inventor(s): LEWIS JASON ERIC [US]; JIANG XIAOMEI JANE [US]

Abstract

An inverted organic solar photovoltaic cell is described that may be fabricated onto rigid or flexible substrates using spray-on technology to apply the various layers of the cell. Indium tin oxide with a thin layer of cesium carbonate functions as the cathode for the novel inverted cells. An active layer of poly-3(hexylthiophene) and [6,6]-phenyl C61-butyric acid methylester having a thickness around 200 nm to 600 nm facilitates a high level of light transmittal through the cell. A modified PEDOT:PSS, made by doping a conductive polymer with dimethylsulfoxide (DMSO), functions as the anode. A method of forming the inverted organic solar photovoltaic cell is also described using gas-propelled spraying to achieve thin layers. After the layers are formed, the cell is sealed using a vacuum and temperature-based annealing and encapsulation with UV-cure epoxy.

Phil’s Comments:

These applications are going through the patent office examination process so it is difficult to comment on the claims until we know what will actually be allowed.  The claims do make reference to spraying and the second application indicates that nitrogen is used as a propellant.

The device is an inverted solar cell design and may be fabricated onto both rigid and flexible substrates. Exemplary substrates include cloth, glass, and plastic. For example, the substrate may be a low alkaline earth boro-aluminosilicate glass.

Two figures from the second application are shown below:

FIG. 1 is a diagram that depicts the modified PEDOT:PSS as it is sprayed onto the substrate through a stainless steel shadow mask with an airbrush. Nitrogen is used as the carrier gas at a pressure of 20 psi.

FIG. 13 is a diagram showing the cross sectional view of the device architecture of an inverted solar array showing series connection

Figure 1 Capture2

Inorganic Nanoparticle Inks for Printed Electronics

Silicon ink has sometimes been described as a “Dream Material” for printed electronics.  Conductive or semi-conductive inks that can be printed directly onto a variety of substrates to create transistors or other electronic devices have been talked about and promoted for a number of years but few companies have succeeded in commercializing products for the mass market.  Silicon ink has been promoted as an enhancer for the production of solar cells to squeeze an extra few percent efficiency from the panel.  One Silicon-valley company NanoGram Corp. acquired last year by the Teijin Group has developed a silicon ink using a laser pyrolysis method to create stable nanoparticles in a dispersion that can be printed by various means including spin coating and inkjet processes.

A recent patent from NanoGram US8263423 was granted on 11 Sept 2012 and completes a trio of US patents granted for their silicon ink approach.  The other patents are US7993947 and US7892872.  These patents all claim a priority date of 3 Jan 2007 for the US provisional application first filed.  The text of all three patents is more or less the same but differs in the claims, each one covering a different aspect of the invention.  The basic technology is described in the first section “Field of the Invention”:

The invention relates to dispersions/inks of silica/germania particles, such as doped silica particles. The invention further relates to inks that are suitable for ink jet printing. Additionally, the invention relates to the use of doped silica/germania particles for the doping of semiconductor substrates, such as through the drive in of dopants with heat and/or light from a silica/germania deposit formed through inkjet printing onto the semiconductor surface.

The three patents break down the invention into i) the dispersion and method for making the dispersion; ii) the method for depositing the dispersion onto a substrate (inkjet printing); and iii) the method for forming solar cells and optical components.

The following paragraph from the text was selected to describe the dispersion approach:

The dispersions comprise a liquid and the dispersed silica particles, which may or may not be surface modified. In general, silica particles formed by laser pyrolysis can be well dispersed in water or alcohols at moderate concentrations with no surface modification, although higher concentration dispersions generally can be formed with surface modification. Suitable alcohols include, for example, small aliphatic alcohols, such as methanol, ethanol, propylene glycol, butanediol, mixtures thereof and the like. Upon surface modification, the silica particles can be dispersed in a broader range of solvents and solvent blends through the matching of the chemical properties of the surface modifying agent with the liquid. Thus, following surface modification, the particles can be well dispersed in a range of less polar solvents, such as ethyl lactate, n-methylpyrrolidinone, gamma-butyl lactone, and the like.

The following paragraph was selected to illustrate the printing approach:

While various coating and printing approaches are suitable, inkjet printing offers desirable features with respect to speed, resolution and versatility with respect to real time selection of deposition patterning while maintaining speed and resolution. However, practical deposition using inkjet printing with inorganic particles requires dispersion properties that have not been available prior to development of both the techniques to form high quality silica nanoparticle along with the improved ability to form high quality dispersions from these particles. Thus, the particles produced using laser pyrolysis combined with the improved surface modification approaches and dispersion techniques provides for the formation of inks that are amenable to inkjet deposition.

The following paragraphs were selected to describe the solar cell modifications:

To deliver dopant into the semiconductor from the silica deposit, the material is heated. For example, the structure can be placed into an oven or the like with the temperature set to soften the particles such that the dopants can diffuse into the substrate. The time and temperature can be adjusted to yield a desired dopant migration into the substrate…

Following the drive in of the dopant, it may or may not be desirable to remove the silica. For photovoltaic applications it is generally desirable to remove the silica to expose the doped semiconductor for the application of conductive electrical contacts. To remove the silica, the oxide can be etched, for example, using conventional approaches, such as using wet (chemical) etching or plasma etching.

Of course, you would need to review the claims to see exactly what has been allowed by the examiner and to understand the scope of the granted patent.

Phil’s Comments

It is quite common to see a provisional patent application emerge as several patents described as continuations of the first or earlier patent.  These can also appear as divisional patents and arise because the patent examiner or inventor has noted that the original application contains more than one invention.  These days the examiners are more strict in ensuring that the method and the material inventions are separated out.  In this case the distinction between the dispersion, the printing method and the application to solar cells or optical displays has been identified and separated into the three patents reviewed here.

I have not seen any recent evidence that the Teijin group have announced any products based on this approach and about 1 year has elapsed since they were actively promoting the technology.  It has been a tough year for solar cell manufacturers and a number of promising companies exploring plastic electronics approaches have filed for bankruptcy (e.g. Konarka and Novasolar).  It remains to be seen whether the silicon ink approach will be adopted as a means to increase efficiency and lower cost of conventional solar cells.

Can you really spray on Solar cells?

Back in January 2010 New Energy Technologies unveiled a patent pending process for “spraying” solar panels and their related components onto glass.  The spray concept seemed to catch the publics imagination and of course the idea that you could simply spray from a can onto glass and have a functioning solar window does indeed seem a fantastic breakthrough.  The reality is somewhat different and while the research does indeed show that functional organic layers can be spray coated onto a substrate this is but one step of a multi-phase process to create a fully functional solar panel.

Although the patent applications had been filed a considerable period has to elapse before they become published and available in the public domain.  Earlier this month one of the US patent applications was published and so it is possible to delve a bit deeper into the technology that is being developed.  The research is based on the work of Professor Xiaomei Jiang in the Nanostructure Optoelectronics Lab at the University of South Florida.  New Energy Technologies Inc. are in the process of developing their SolarWindow™ product using this technology.  More recently they have entered into a cooperative Research and Development agreement with the US Department of Energy’s National Renewable Energy Lab. to advance development of SolarWindow™.

The patent application is US20120156825 and summary details are shown below:

Title: Transparent Contacts Organic Solar Panel by Spray

Inventors: Jason Lewis, Jian Zhang, Xiaomei Jiang

Assignee: University of South Florida

Abstract: A method of fabricating organic solar panels with transparent contacts. The method uses a layer-by-layer spray technique to create the anode layer. The method includes placing the substrate on a flat magnet, aligning a magnetic shadow mask over the substrate, applying photoresist to the substrate using spray photolithography, etching the substrate, cleaning the substrate, spin coating a tuning layer on substrate, spin coating an active layer of P3HT/PCBM on the substrate, spray coating the substrate with a modified PEDOT solution, and annealing the substrate.

Claims: The first six claims are worth noting:

1. A method of fabricating organic solar panels with transparent contacts, comprising: applying photoresist to a substrate by spray photolithography; spin coating a tuning layer on the substrate; spin coating an active layer coating on the substrate; spray coating the substrate with a modified PEDOT solution; and annealing the substrate.

2. The method of claim 1, wherein the substrate is an ITO glass substrate.

3. The method of claim 1, wherein the substrate is plastic.

4. The method of claim 1, wherein the substrate is cloth.

5. The method of claim 1, wherein the tuning layer is Cs2CO3.

6. The method of claim 1, wherein in the active layer coating is P3HT/PCBM.

There are an additional 17 claims which give further details of the method.

Phil’s comments:  As you can see the concept of simply spraying a solar cell onto glass is a long way from reality.  However, this patent application does explain the technical approach quite well and indicates that the various layers including the contacts are all transparent so that the final result is a solar cell on glass that will still resemble a window.

Fujifilm files patent for flexible solar cell technology

Fujifilm used to be a major competitor when I was involved in photographic film and plate manufacture for Kodak.  It is interesting to see that they have converted their expertise in these areas to the fabrication of flexible Aluminium based films for solar cell technology.  In a recent announcement Fujifilm Corp announced they have formed a CIGS photovoltaic (PV) cell on an aluminum flexible substrate and achieved a conversion efficiency of 17.6% with an aperture area of 0.486cm2.  Also, they confirmed a conversion efficiency of 12.5% with an aperture area of 72cm2.

Interestingly a US patent application (US20100224249) appeared just a few days ago covering this technology.  Fujifilm used anodic oxidation to form an aluminium oxide (Al2O3) layer on an aluminium foil as the substrate which is treated with a diffusion barrier layer of either titanium or chromium. On the substrate, a molybdenum (Mo) layer, CIGS layer, cadmium sulfide (CdS) layer and zinc oxide (ZnO) layer are stacked. Furthermore, sodium doping is used to increase conversion efficiency.  Full details can be found in their concrete examples 1 and 2.  A comparison with an example not containing the diffusion barrier layer had a lower conversion efficiency.