Integration of Light Trapping Silver Nanostructures in Hydrogenated Microcrystalline Silicon Solar Cells by Transfer Printing

The overall goal of this transfer printing technique is to provide viable methodology to integrate functional plasmonic nanostructures in devices such as solar cells. This method can help to progress the practical device application of meta nano structures such as prismic solar cells. The main advantage of this technique is that one can quickly introduce, desired, or designed meta nano structures into existing device structures result significant changes in the original fabrication process.

Though this method has been developed, especially for solar cells, it can be also applied to other devices using plasmonic properties such as right emitting diodes and sensors. To begin set a nano hole mold into a polytetrafluoroethylene container. Next place, 0.76 grams of vinyl methyl suboxane dimethyl suboxane copolymer into a disposable glass bottle.

Use a micro pipette with a disposable polypropylene tip to add six microliters of platinum di vinyl tetraethyl dioxane complex to the copolymer. Next, use a micro pipette with a disposable polypropylene tip to add 24 microliters of 2 4 6 8 tetraethyl tetra vinyl cyclo tetra suboxane to the copolymer, and mix the solution. Briefly alter these volumes if necessary, to remain at the same ratio with the copolymer.

Then add 240 microliters of methyl hydros, laane dimethyl suboxane copolymer to the glass bottle, and mix it quickly Using a disposable glass pipette, blow the surface of the mixture with nitrogen briefly, and then pour the resulting hard PDMS pre polymer onto a commercially available patterned mold that has been placed on a spin coter spin coat the mold at 1000 RPM for 40 seconds to achieve a layer thickness of about 40 microns. Then place the spin coated sample into a preheated chamber at 65 degrees Celsius for 30 minutes. To briefly cross-link the hard PDMS during the heating mix six grams of silicone with 0.6 grams of catalyst in a disposable glass bottle.

Vary the amount of catalyst if necessary to keep a one to 10 ratio with the silicone. Then place the glass bottle in a vacuum desiccate and apply a vacuum of about 133 Pascals for 15 minutes to degas the mixture. Next, quickly pour the DGAs mixture onto the heated mold in order to create a soft PDMS layer about three millimeters thick.

Place the resulting sample back into the vacuum desiccate and degas the sample for an additional hour. Then transfer the Degas sample into the heating chamber and heat from room temperature up to 80 degrees Celsius at a rate of about three degrees Celsius per minute. Keep the sample at 80 degrees Celsius for five hours to cross-link the hard and soft PDMS completely after cooling the sample down to room temperature.

Peel off the PDMS stamp carefully from the mold. Reuse the mold up to five times to prepare additional stamps if needed. Cut the resulting nano pillar stamp into seven millimeter by seven millimeter pieces using a knife and store them under air until they are used.

Additionally, prepare the block copolymer binding layer solution and hydrogenated microcrystalline silicone substrates as described in the accompanying text protocol. Wash the PDMS stamps in 30 milliliters of ethanol using an ultrasonic bath for 15 minutes, and then dry the stamp by blowing it with pure nitrogen. Next, use double-sided adhesive tape to affix the cleaned PDMS stamps onto a sample holder.

Then place the samples into an electron beam evaporation system and deposit a 10 to 80 nanometer thick silver film onto the stamps using a deposition rate of five to 10 angstroms per second and a pressure of about 3.5 times 10 to the minus four pascal. Take out the silver coated stamps from the evaporation system and use them immediately in the transfer printing step. Take the thin film silicon substrates prepared as described in the accompanying text protocol and spin coat them with 0.3 milliliters of the block copolymer binding solution at 5, 000 RPM for 40 seconds.

Next, wet the surface of the coated substrates with ethanol using a digital micro pipette, and then apply the silver coated PDMS stamp softly to the ethanol wet surface. Do not press the stamp When you apply the PDM stamp to the subrate. Please avoid pressing it.

Just pressing is enough. The stamp spontaneously makes an intimate contact between the surface rate due to the surface tension of ethanol. Next place the thin film silicon substrate along with a stamp into a vacuum chamber and apply vacuum of about 133 pascals.

After five minutes, fill the vacuum chamber with air and take out the thin film silicon substrate. Remove the stamp from the thin film silicon substrate by holding both sides of the stamp tweezers to transfer print silver nano disks. If successful, the trace of stamping is visible as a greener spot.

Rinse the transferprinted thin film silicon substrate with a continuous flow of ethanol for 15 seconds, and then dry the substrate by blowing on it with nitrogen gas. Next place the transfer printed thin film silicon substrate into the process chamber of an Argonne plasma system. Pump out the air in the process chamber for about five minutes in order to achieve a pressure of about 20 pascals.

Then open the valve of the Argonne gas line and manually adjust the flow rate to about four SCCM or whatever flow rate is necessary to generate plasma. Wait for about five minutes for the pressure to stabilize to 40 Pascals. Then turn on the system to generate Argonne plasma for 108 seconds.

Finally, close the valve of the gas line, stop pumping and fill air into the process chamber to take out the plasma cleaned, transfer printed thin film silicon substrates. Follow the remainder of the accompanying text protocol for details on how to complete the fabrication of the thin film silicon solar cell and measure its efficiency and output. These scanning electron microscopy images of the resulting silver nano disc array on hydrogenated microcrystalline silicon substrates clearly display some of the nanoscale features incorporated into the design.

The diameter of the nano discs averages 200 nanometers. The center to center distance averages 460 nanometers and the thickness of the silver nano discs averaged 40 nanometers. The external quantum efficiency spectra of the fabricated cells are shown here compared to a reference cell.

The silver nano disc incorporated cell showed higher signals in the long wavelength range of 650 to 1, 100 nanometers. Such wavelength selective enhancement clearly indicates the preferential effect of the plasmon active silver nano discs for solar cell use. Namely plasmonic light trapping Once must that the transfer printing process can be completed in less than 30 minutes if it is performed properly.