Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y10/00—Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
  • H10K71/00—Manufacture or treatment specially adapted for the organic devices covered by this subclass
  • H10K71/10—Deposition of organic active material
  • H10K71/12—Deposition of organic active material using liquid deposition, e.g. spin coating
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
  • H10K2102/00—Constructional details relating to the organic devices covered by this subclass
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
  • H10K30/00—Organic devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation
  • H10K30/30—Organic devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation comprising bulk heterojunctions, e.g. interpenetrating networks of donor and acceptor material domains
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
  • H10K30/00—Organic devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation
  • H10K30/50—Photovoltaic [PV] devices
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
  • H10K85/00—Organic materials used in the body or electrodes of devices covered by this subclass
  • H10K85/10—Organic polymers or oligomers
  • H10K85/111—Organic polymers or oligomers comprising aromatic, heteroaromatic, or aryl chains, e.g. polyaniline, polyphenylene or polyphenylene vinylene
  • H10K85/113—Heteroaromatic compounds comprising sulfur or selene, e.g. polythiophene
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
  • H10K85/00—Organic materials used in the body or electrodes of devices covered by this subclass
  • H10K85/10—Organic polymers or oligomers
  • H10K85/111—Organic polymers or oligomers comprising aromatic, heteroaromatic, or aryl chains, e.g. polyaniline, polyphenylene or polyphenylene vinylene
  • H10K85/113—Heteroaromatic compounds comprising sulfur or selene, e.g. polythiophene
  • H10K85/1135—Polyethylene dioxythiophene [PEDOT]; Derivatives thereof
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
  • H10K85/00—Organic materials used in the body or electrodes of devices covered by this subclass
  • H10K85/20—Carbon compounds, e.g. carbon nanotubes or fullerenes
  • H10K85/211—Fullerenes, e.g. C60
  • H10K85/215—Fullerenes, e.g. C60 comprising substituents, e.g. PCBM
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E10/00—Energy generation through renewable energy sources
  • Y02E10/50—Photovoltaic [PV] energy
  • Y02E10/549—Organic PV cells
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
  • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

• This invention relates to spray-manufactured organic solar photovoltaic cell. Specifically, the invention provides a novel method of manufacturing organic solar photovoltaic cells using spray-deposition and the organic solar photovoltaic cell resulting therefrom.
• Photovoltaic cells have been used since the 1970s as an alternative to traditional energy sources. Because photovoltaic cells use existing energy from sunlight, the environmental impact from photovoltaic energy generation is significantly less than traditional energy generation. Most of the commercialized photovoltaic cells are inorganic solar cells using single crystal silicon, polycrystal silicon or amorphous silicon. Traditionally, solar modules made from silicon are installed on rooftops of buildings. However, these inorganic silicon- based photovoltaic cells are produced in complicated processes and at high costs, limiting the use of photovoltaic cells. These silicon wafer-based cells are brittle, opaque substances that limit their use, such as on window technology where transparency is a key issue. Further, installation is an issue since these solar modules are heavy and brittle.
• a photoactive material including an electron donor material and an electron acceptor material is sandwiched between the anode and the cathode.
• the donor material in conventional devices is poly-3- hexylthiophene (P3HT), which is a conjugated polymer.
• the conventional acceptor material is (6,6)-phenyl C 61 butyric acid methylester (PCBM), which is a fullerene derivative.
• PCBM poly-3- hexylthiophene
• Both the ITO and aluminum contacts use sputtering and thermal vapor deposition, both of which are expensive, high vacuum, technologies. In these photovoltaic cells, light is typically incident on a side of the substrate requiring a transparent substrate and a transparent electrode. However, this limits the materials that may be selected for the substrate and electrode.
• the organic photoelectric conversion layer is sensitive to oxygen and moisture, which reduce the power conversion efficiency and the life cycle of the organic solar cell.
• Development of organic photovoltaic cells has achieved a conversion efficiency of 3.6% (P. Peumans and S. R. Forrest, Appl. Phys. Lett. 79, 126 (2001)).
• the photovoltaic process in OPV first starts from the absorption of light mainly by the polymer, followed by the formation of excitons. The exciton then migrates to and dissociates at the interface of donor (polymer)/acceptor (fullerene). Separated electrons and holes travel to opposite electrodes via hopping, and are collected at the electrodes, resulting in an open circuit voltage (V oc ). Upon connection of electrodes, a photocurrent (short circuit current, l sc ) is created.
• These polymeric OPV holds promise for potential cost-effective photovoltaics since it is solution processable.
• ITO a transparent conductor
• OPV hole collecting electrode
• cathode the electron accepting electrode
• ITO-free wrap through by Zimmermann et.al. (Zimmermann, et al., ITO-free wrap through organic solar cells— A module concept for cost-efficient reel-to-reel production.
• Sol. Energy Mater. Sol. Cells, 2007, 91(5), 374) another approach is to add an electron transport layer onto ITO to make it function as cathode.
• Inverted geometry OPVs in which the device was built from modified ITO as cathode first have been studied both in single cells (Huang, et al., A Semi- transparent Plastic Solar Cell Fabricated by a Lamination Process. Adv. Mater.
• photoactive layers were developed using a low-molecular weight organic material, with the layers stacked and functions separated by layer.
• the photoactive layers were stacked with a metal layer of about 0.5 to 5 nm interposed to double the open end voltage (V 00 ).
• V 00 open end voltage
• stacking photoactive layers can cause layers to melt due to solvent formation from the different layers. Stacking also limits the transparency of the photovoltaic. Interposing a metal layer between the photoactive layers can prevent solvent from one photoactive layer from penetrating into another photoactive layer and preventing damage to the other photoactive layer. However, the metal layer also reduces light transmittance, affecting power conversion efficiency of the photovoltaic cell.
• a thin film organic solar array is fabricated employing this layer-by-layer spray technique onto desired substrates (can be rigid as well as flexible). This technology eliminates the need for high-vacuum, high temperature, low rate and high-cost manufacturing associated with current silicon and in-organic thin film photovoltaic products.
• the organic solar photovoltaic cell is manufactured on an ITO-coated substrate, such as cloth, glass, plastic or any material known in the art for use as a photovoltaic substrate.
• plastics include any polymer such as acrylonitrile butadiene styrene (ABS), acrylic (PMMA), cyclic olefin copolymer (COC), ethylene-vinyl acetate (EVA), ethylene vinyl alcohol (EVOH), fluoroplastics, such as PTFE, FEP, PFA.CTFE, ECTFE, and ETFE, Kydex (an acrylic PVC alloy), liquid crystal polymer (LCP), polyoxymethylene (POM or Acetal), polyacrylates (acrylic), polyacrylonitrile (PAN or acrylonitrile), polyamide (PA or nylon), polyamide-imide (PAI), polyaryletherketone (PAEK or ketone), polybutadiene (PBD), polybutylene (PB), polychlorotrifluoroethylene (PCT
• the ITO layer was optionally patterned onto the first face of the glass, forming an anode, by obtaining an ITO-coated substrate, patterning the ITO using photolithography, etching the ITO, and cleaning the etched ITO and substrate.
• the ITO may be etched with a mixed solution of HCI and HN0 3 .
• the etched ITO and substrate was then optionally cleaned by at least one of acetone, isopropanol, or UV-ozone. The cleaning step may be performed at 50 °C for 20 min each, followed by drying with N 2 .
• a layer of Cs 2 C0 3 was prepared and sprayed onto the etched ITO substrate.
• the layer of Cs 2 C0 3 was prepared by dissolving Cs 2 C0 3 in 2-ethoxyethanol at a ratio of 2 mg/ml, and stirred for 1 hour.
• the layer was annealed to the OPV cell inside a glovebox.
• the annealing step occurred at 150 °C for 10 min inside the N 2 glovebox.
• the Cs 2 C0 3 layer has an optional thickness of about 5 to about 15 .
• an active layer of P3HT and PCBM was prepared and sprayed onto the OPV cell.
• the active layer solution was optionally prepared my mixing P3HT and PCBM with a weight ratio of 1 :1 in dichlorobenzene.
• the active layer was then optionally stirred on a hotplate for 48h at 60 °C prior to spraying.
• the OPV cell was dried in an antechamber under vacuum for at least 12 hours.
• the the active layer of has an optional layer thickness of about 100nm to about 500 nm, depending on the organic photovoltaic cell materials and transparency requirements.
• a layer comprising poly (3,4) ethylenedioxythiophene:poly-styrenesulfonate and 5 vol.% of dimethylsulfoxide was then disposed on the active layer, providing the cathode for the photovoltaic cell.
• the poly (3,4) ethylenedioxythiophene:poly-styrenesulfonate mixed with 5 vol.% of dimethylsulfoxide was prepared diluting the poly (3,4) ethylenedioxythiophene:poly- styrenesulfonate filtering the diluted poly (3,4) ethylenedioxythiophene:poly-styrenesulfonate through a 0.45 ⁇ filter, and mixing the dimethylsulfoxide into the diluted poly (3,4) ethylenedioxythiophene:poly-styrenesulfonate.
• this cathodic layer has a thickness of about 100nm to about 700nm, and may be 600nm in some variations. Exemplary thicknesses include 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 550nm, 600nm, 650nm, and 700nm.
• the OPV cell was placed into high vacuum for 1 h, such as at 10 ⁇ Torr.
• the OP cell was then annealed at 120°C, 160°C, or at 120°C for 10 minutes followed by high vacuum for 1 hour and annealing at 160 °C for 10 minutes and encapsulated with a UV-cured epoxy.
• the photovoltaic cells may also be in electrical connection, thereby forming an array.
• a series of organic solar photovoltaic cells disposed into an array of 50 individual cells having active area of 12mm 2 .
• the array comprises 10 cells disposed in series in one row, and 5 rows in parallel connection in some variations.
• the inventive device and method has solved the costly and complicated process currently used to make crystalline and thin film solar cells, namely, high-vacuum, high temperature, low rate and high-cost manufacturing. Furthermore, this technology could be used on any type of substrate including cloth and plastic. This new technology enables all solution processable organic solar panel on with transparent contacts. This technique has great potential in large- scale, low-cost manufacturing of commercial photovoltaic products based on solutions of organic semiconductors.
• SAM self assembled molecules
• Fig. 1 is a diagram showing a perspective view of the novel inverted OPV cells containing sprayed-on layers.
• Figures 2(A) and (B) are images of the device structure of an inverted test device. (A) top view; (B) side view.
• Figure 3 is a graph showing the l-V characteristics of three test devices without Cs 2 C0 3 layer (black solid line), and with Cs 2 C0 3 layer at difference thickness (black line with empty triangle and line with filled triangle).
• Figures 4(A) and (B) are graphs showing the comparison of (A) transparency and (B) resistance between ITO and the anode (modified PEDOT SS) at different thickness.
• Figure 5 is a graph showing the transmission spectra of an active layer (P3HT:PCBM) of 500nm (black line with filled square), and with a m-PEDOT:PSS layer of 600nm (gray line with filled circle).
• P3HT:PCBM active layer
• m-PEDOT:PSS layer 600nm
• Figure 6 is a top-view image of the device architecture of an inverted array having 50 cells in the array.
• Figure 7 is a side-view image of the device architecture of an inverted array.
• Figure 8 is a graph showing the IV of four test cells measured with AM1.5 solar illumination under various annealing conditions: 1-step annealing at 120°C (light grey filled circle), or 160°C (black filled square), and 2-step annealing (dark grey filled triangle).
• Figure 9 is a graph showing the IPCE of four test cells measured under tungsten lamp illumination at various annealing conditions: 1-step annealing at 120°C (light grey filled circle), or 160°C (black filled square), and 2-step annealing (dark grey filled triangle).
• Figure 10 is a graph showing the IV of 4 inverted spray-on array measured with AM1.5 solar illumination under various annealing conditions: 1-step annealing at 120°C (dashed line), or 160°C (light grey thin line), and 2-step annealing (black filled square). These 3 arrays use m- PEDOT 500 as anode. The 4 th array (thick dark grey line) uses m-PEDOT 500 as anode and was annealed at 160°C
• Figure 11 is a graph showing the improvement of IV of an inverted array under continuous A 1 .5 solar illumination. The first measurement was done right after the array was fabricated and encapsulated.
• Figure 12 is an image showing the transparency of manufactured sprayed solar array using using the disclosed methods.
• ITO indium tin oxide
• Corning® low alkaline earth boro- aluminosilicate glass having a nominal sheet resistance of 4-10 Ohm/ square (Delta Technology, Inc.) using standard photolithography method and cleaned following the procedure described elsewhere (Lewis, et al., Fabrication of organic solar array for applications in microelectromechanical systems. Journal of Renewable and Sustainable Energy 2009, 1, 013101 -9).
• 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% HCI-7%HN0 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. An interstitial layer was formed on top of the patterned ITO layer. A solution of 0.2% wt. Cs 2 C0 3 (2 mg/mL; Sigma-Aldrich Co. LLC, St. Louis, MO) in 2-ethoxyethanol was prepared and stirred for one hour at room temperature.
• Cs 2 C0 3 was chosen to reduce ITO work function close to 4.0 eV to be utilized as cathode.
• the Cs 2 C0 3 solution was sprayed onto the clean ITO substrate through a custom made shadow mask with an airbrush using N 2 set to 20 psi from a distance of about 7-10 centimeters.
• the product was then annealed for 10 minutes at 150°C in an N 2 glovebox (MOD-01 ; M. Braun Inertgas-Systeme GmbH, Garching German).
• the active layer solution was prepared by mixing separate solutions of a high molecular weight poly(3-hexylthiophene (P3HT with regioregularity over 99% and average molecular weight of 42K; Rieke Metals, Inc., Lincoln, NE) and 6,6-phenyl C61 butyric acid methyl ester (PCBM, C 60 with 99.5% purity; Nano-C, Inc., Westwood, MA) at a weight ratio of 1 :1 in dichlorobenzene at 20 mg/mL and stirred on a hotplate for 48 hours at 60°C.
• the active coating was then spray coated onto the Cs 2 C0 3 coated substrate using an airbrush with N 2 set to 30psi.
• the airbrush was set at about 7-10cm away from the substrate and multiple light layers of active layer were sprayed, resulting in a layer thickness of about 200 to about 300nm.
• the device is then left to dry in the antechamber under vacuum for at least 12 hours. After drying, excess active layer solution was wiped off of the substrate using dichlorobenzene (DCB)-wetted cotton followed by isopropanol-wetted cotton.
• DCB dichlorobenzene
• 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.
• This filtered solution of PEDOT:PSS is mixed with 5 vol.% of dimethylsulfoxide to increase conductivity (Lim, et al., Spray-deposited poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) top electrode for organic solar cells. Appl. Phys. Lett. 2008, 93, 193301 ).
• 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 2 ) as the carrier gas, set to 30 psi with the airbruch positioned about 7-10 cm from the substrate.
• 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 " * Torr) for 1 h, followed by a substrate annealing at 120-160°C for 10min.
• the modified PEDOTiPSS (m- PEDOT) was then sprayed onto the substrate using a custom made spray mask.
• the finished device was placed into high vacuum (10 "6 Torr) for 1 h.
• This step was shown to improve the device performance with sprayed active layer (Lim, et al., Spray-deposited poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) top electrode for organic solar cells. Appl. Phys. Lett. 2008, 93, 193301 ).
• the final device was annealed at various conditions, including 120°C, 160°C, and step step annealing comprising 120°C for 10 minutes followed by high vacuum for 1 hour and annealing at 160°C for 10 minutes.
• the annealed device was encapsulated using a UV-cured encapsulant (EPO-TEK OG142-12; Epoxy Technology, Inc., Billerica, MA) was applied to the edge of the encapsulation glass, and the glass is placed into the glovebox for at least 15min, 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 15min of UV to cure the encapsulant epoxy.
• EPO-TEK OG142-12 Epoxy Technology, Inc., Billerica, MA
• Inverted organic photovoltaic cell 1 seen in Figure 1 , was created using the method described in Example 1 , using pre-cut 4"x4" ITO glass substrates with a nominal sheet resistance of 4-10 Ohm/ square and Corning® low alkaline earth boro-aluminosilicate glass (Delta Technology, Inc., Tallahassee, FL).
• Inverted photovoltaic cell 1 was composed of different layers of active materials and terminals (anode and cathode) built onto substrate 5.
• Interstitial layer 40 covers anode 10, except for the outermost edges, as seen in Figure 2(A), and permits ITO to be used as an anode as discussed in Example 1.
• 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 ⁇ X 4 im array was found to possess over 30% transparency.
• An inverted single-cell test device was used as a starting point to ensure a good reference point for the multi-cell array, which consists of four identical small cells (4mm 2 ) on a 1 " x1 " substrate, as seen in Figure 2(B).
• the cell is sandwiched between two cross electrodes, designated as 50 and 51.
• the test device was fabricated using the same procedure described in Example 1 , with m-PEDOT 500 as anode.
• ITO normally has a work function of ⁇ 4.9eV.
• the function of ITO in a traditional OPV device is as an anode.
• an electron transport layer such as ZnO (Jingyu Zou, et al., Metal grid/conducting polymer hybrid transparent electrode for inverted polymer solar cells. Appl. Phys. Lett. 2010, 96, 203301), Ti0 2 (Huang, et al., A Semi-transparent Plastic Solar Cell Fabricated by a Lamination Process. Adv. Mater. 2008, 20(3), 415; Bang-Ying Yu, et al., Efficient inverted solar cells using Ti0 2 nanotube arrays.
• Figure 3 shows how the Cs 2 C0 3 layer affects the performance of the inverted cell.
• the control cell without Cs 2 C0 3 black solid line
• V oc (0.03V).
• the difference between the present invention and previous work can be explained by the use of an electron transport layer to alleviate non-ohmic contact with the cathode (PEDOT in this case) in their work.
• PEDOT cathode
• Cs 2 C0 3 was spin coated on to the cleaned ITO substrate in these devices.
• the optimal thickness of Cs 2 C0 3 layer was achieved at a spin rate of 5000rpm. At higher rate of 7000rpm, the device was less efficient owing to the fact of a discontinuous Cs 2 C0 3 layer. The optimal thickness was later determined to be around 15A.
• the l-V was measured by shining light from m- PEDOT side.
• the device was analyzed by exposing the cell to continuous radiation.
• the current-voltage (l-V) characterization of the solar array was performed with a 1.6 KW solar simulator under AM1 .5 irradiance of 100 mW/cm 2 (Newport Corp., Franklin MA). No spectral mismatch with the standard solar spectrum was corrected in the power conversion efficiency (PCE) calculation.
• the incident photon converted electron (IPCE), or the external quantum efficiency, of the device was measured using 250W tungsten halogen lamp coupled with a monochromator (Newport Oriel Cornerstone 1/4 m).
• the photocurrent was detected by a UV enhanced silicon detector connected with a Keithley 2000 multimeter.
• Example 2 An inverted single-cell test device was prepared, as discussed in Example 1 , but using different thicknesses of m-PEDOT to determine cell characterisctics at different cell thicknesses.
• ITO was chose as a reference for comparison.
• the transparency of m-PEDOT is about 80%, comparable with ITO, as seen in Figure 4(A).
• the resistance decreases as thickness increases, which is consistent with the bulk model, seen in Figure 4(B).
• the trade-off between transparency and resistance is another important fabrication parameter.
• the current array was fabricated with thickness of about 600nm, which has moderate resistance of 70ohm/square, and transparency about 50%.
• a solar array was prepared, as disclosed above, comprising 50 individual cells each has active area of 12mm 2 , seen in Figure 6. The array was configured with 10 cells in series to increase in one row to increase voltage, and 5 rows in parallel connection to increase current, seen in cross section in Figure 7. The arrays were prepared with have m-PEDOT 750 or m- PEDOT 500 as semitransparent anode.
• Annealing has shown to be the most important factor to improve organic solar cell performance (Shaheen, Brabec, Sariciftci, Padinger, Fromherz, and Hummelen, Appl. Phys. Lett. 2001, 78, 841 ; Padinger, et al., Effects of Postproduction Treatment on Plastic Solar Cells. Adv. Fund. Mater. 2003, 13(1), 85-88).
• Cells were exposed to a 1.6 KW solar simulator under AM 1.5 irradiance of 100 mW/cm 2 (Newport Corp., Franklin MA).
• the second annealing step at 160°C worsens the device performance, mainly due to unfavorable change of film morphology, which was confirmed in AFM images (data not shown).
• the PCE of 1 -step annealing at 160°C was in between that of 1 -step annealing at 120°C and 2-step annealing, yet the device has the worst FF.
• Table 1 listed the details of the IV characteristics of these three test cells.
• IPCE measurement shows 2-step annealing was worse than 1 step annealing, seen in Figure 9, which was consistent with IV measurements (data not shown).
• IPCE measurement was done under illumination from Tungsten lamp, whereas IV was done under solar simulator which has different spectrum than that of the tungsten lamp. Nevertheless, the integration of IPCE should be proportional to l sc .
• AFM images of topography and phase of 4 different test arrays at different annealing conditions an as-made cell, made using the method of Example 1 without annealing, having a roughness of 7.41 nm, 1-step annealing at 120°C having a roughness of 6.60nm, annealing at 160°C having a roughness of 3.68 nm, and (d) 2-step annealing having a roughness of 9.76 nm.
• the 1-step annealing at 120°C showed the improved film roughness and the best phase segregation of P3HT and PCBM, which explains why the device performance was the best, seen in Figures 8 and 9.
• Device by 2-step annealing has the smoothest film, however, the phase segregation was much less distinct. This indicates that P3HT chains and PCBM molecules are penetrating through each other more after the second annealing at 160°C, and form much smaller nano-domains, which are favorable for charge transport between the domains (Kline and McGehee, Morphology and Charge Transport in Conjugated Polymers. J of Macromol Sci, Part C: Polymer Reviews, 2006, 46(1): 27-45).
• the phenomenon may be a result of the porosity of sprayed film being much larger than the spin- coated film, and polymer chains have much more loose arrangement in sprayed device, with the heat from solar illumination, the polymer chains relax more and the film nanomorphology was improved, with possibly PCBM penetrating into the voids between polymer chains and causing better phase segregation (Geiser, et al., Poly(3-hexylthiophene)/C 60 heterojunction solar cells: Implication of morphology on performance and ambipolar charge collection. Sol. Eng. & Sol. Cells 2008, 92(4), 464). This effect is similar to thermal annealing performed on hot plate.
• a large area organic array was fabricated using the all spay technique described in Example 1.
• a fully encapsulated 4"x4" array was prepared and found to have over 30% transparency, with power conversion efficiency (PCE) as high as 1.80 % under constant illumination of simulated sunlight.
• PCE power conversion efficiency
• Thermal annealing has proven to be essential to improve device PCE, and the optimal annealing conditions are not the same with small single cell and large solar array consisting of 50 cells.
• Systematic studies of optical, electronic and morphologic properties of the device reveals the influence of nanomorphology over device power conversion efficiency.

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