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.


Publication date: 03/10/2013



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.


Publication date: 10/10/2013



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

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.

The Millenium Technology Prize for 2010 awarded to Prof. Michael Grätzel

The 2010 Millennium Prize Laureate Michael Grätzel is the father of third generation dye-sensitized solar cells. Grätzel cells, which promise electricity-generating windows and low-cost solar panels, have just made their debut in consumer products.  The technology often described as ‘artificial photosynthesis’ is a promising alternative to standard silicon photovoltaics. It is made of low-cost materials and does not need an elaborate apparatus to manufacture. Though DSC cells are still in relatively early stages of development, they show great promise as an inexpensive alternative to costly silicon solar cells and an attractive candidate for a new renewable energy source.

The key patent describing Grätzel’s invention was first filed as a GB patent with a priority date of 17th April 1990.  The technology was published in Nature in 1991 and the first patents were granted in 1994.  US5350644B1 was published on 27th Sept 1994 and has now been cited by over 70 other patents indicating the significance of this invention.  However, it was not until 2009 that mass production of the solar cells began.

The opening sentence of the patent very simply states the essence of the invention: “The invention relates to new transition metal dyestuffs and to their use in photovoltaic cells. These dyes can be coated on titanium dioxide films rendering such devices effective in the conversion of visible light to electric energy”

The first claim reads as follows:

  1. A solar-light-responsive photovoltaic cell comprising a first electrode comprising

    i) a light transmitting electrically conductive layer deposited on a glass plate or a transparent polymer sheet;

    ii) at least one porous, high surface area titanium dioxide layer applied to said light transmitting electrically conductive layer;

    iii) a dopant applied to at least the outermost titanium dioxide layer, optionally also to the second to the outermost and third to the outermost layer, said dopant being selected from a divalent metal ion, trivalent metal ion, and boron; and

    iv) a photosensitizer applied to the dopant-containing TiO2 layer, said photosensitizer being attached to the TiO2 layer by means of interlocking groups, said interlocking groups being selected from carboxylate groups, cyano groups, phosphate groups and chelating groups with conducting character selected from oximes, dioximes, hydroxy quinolines, salicylates, and α-keto-enolates.

Wake Forest University: Patent granted for Fibre-Solar Cell Technology

EP2022108B1 was granted last year and provides the University with a first patent for a new solar-cell technology that can double the energy production of today’s flat cells at a fraction of the cost.  The patent on the technology has been licensed to FiberCell Inc. to develop a way to manufacture the cells. The company, based in the Piedmont Triad Research Park in downtown Winston-Salem, is producing its first large test cells.

The new solar cells are made from millions of miniscule plastic fibres that can collect sunlight at oblique angles – even when the sun is rising and setting.  Flat-cell technology captures light primarily when the sun is directly above.

A diagram from the Fibercell website shows the design structure of the fibre:

First Claim:

1. An apparatus comprising

an optical fiber core (102);
a first electrode (104) surrounding the optical fiber core (102);
at least one photosensitive organic layer (108) surrounding the first electrode (104) and electrically connected to the first electrode (104); and
a second electrode (110) surrounding the organic layer (108) and electrically connected to the organic layer (108).
characterized in that
said first electrode (104) is radiation transmissive.

According to Wake Forrest, to make the cells, the plastic fibers are assembled onto plastic sheets, with a technology similar to that used to create the tops of soft-drink cups. The absorber – either a polymer or a dye – is sprayed on. The plastic makes the cells lightweight and flexible – a manufacturer could roll them up and ship them anywhere cheaply.  A diagram of this arrangement maybe similar to the one found in the patent in Fig. 5 but no details of the manufacture are available.