Alex Miedaner

Fast-Switching Electrochromic Li+-Doped NiO Films by Ultrasonic Spray Deposition

A low cost, high throughput deposition method for films of nickel oxide NiO and lithium-doped nickel oxide with improved electrochromic performance is demonstrated. This method is based on ultrasonic spray deposition of aqueous-based precursor solutions in air at atmospheric pressure, which represents a significant cost savings compared to vacuum deposition methods. The resultant materials are characterized by X-ray diffraction, Raman spectroscopy, electron microscopy, and electrochemical measurements. Electrochromic performance is demonstrated with in situ optical transmission measurements during electrochemical characterization. Nickel oxide materials color anodically and are thereby ideally suited to be used as counter electrode for the well-known tungsten oxide WO3 system in “smart” window applications. The coloration of nickel oxide materials is known to be slow when compared to WO3 and thereby limits the overall response time of a NiO/WO3 tandem device. The analysis of potential step response data shows that our lithium-doped nickel oxide material achieves 90% of its total coloration change in 29 s, which is comparable to reported measurements for WO3. These results significantly mitigate a potential bottleneck to the adoption of metal oxide electrochromic windows not only by demonstrating similar performance between NiO and WO3, but by achieving this result via low cost, highly scalable processing methods.

Multi-Layer Inkjet Printed Contacts for Silicon Solar Cells

Ag, Cu, and Ni metallizations were inkjet printed with near vacuum deposition quality. The approach developed can be easily extended to other conductors such as Pt, Pd, Au, etc. Thick highly conducting lines of Ag and Cu demonstrating good adhesion to glass, Si, and printed circuit board (PCB) have been printed at 100-200degC in air and N2 respectively. Ag grids were inkjet-printed on Si solar cells and fired through the silicon nitride AR layer at 850degC, resulting in 8% cells. Next generation inks, including an ink that etches silicon nitride, have now been developed. Multi-layer inkjet printing of the etching ink followed by Ag ink produced contacts under milder conditions and gave solar cells with efficiencies as high as 12%

Direct write metallization for photovoltaic cells and scaling thereof

Atmospheric solution processing can help toward a significant cost reduction of photovoltaics. We investigate the use of direct write deposition approaches for deposition of metallization for a variety of solar cell materials. We are studying inkjet printing and aerosol spraying of metal contacts for Si, CIS/CIGS and organic photovoltaics. We have developed metal organic decomposition inks for metals such as: silver, nickel, copper and aluminum. All of these can be deposited in lines with 30–40 µm width and conductivities close to that of bulk metals. For silicon photovoltaics materials have been developed to facilitate Ohmic contact formation through an anti reflection coating. Initial research has been focusing on small cells, but in order to transfer the technology to production it has to be demonstrated on large area cells as well. For this the Atmospheric Processing Platform (APP) was developed at NREL. This platform allows us to scale the deposition of the developed inks and processing to large area (Up to 157 mm × 157 mm) and prototype contact patterns. The APP consists of several deposition, processing and characterization units, most located in a controlled environment. The atmospheric deposition tools in the APP are: inkjet printing, aerosol spraying and ultrasonic spraying. A rapid thermal processing unit is integrated for thermal processing. XRF and XRD can be accessed without leaving the controlled environment to determine the composition and structure of the deposited material. Sputter deposition and evaporation are also part of the APP, even though these techniques are not atmospheric. Details of the individual platforms in the APP will be given together with results of direct write contacts on large area cells.

Spray deposition of high quality CuInSe 2 and CdTe films

A number of different ink and deposition approaches have been used for the deposition of CuInSe2 (CIS), Cu(In,Ga)Se2 (CIGS), and CdTe films. For CIS and CIGS, soluble precursors containing Cu, In, and Ga have been developed and used in two ways to produce CIS films. In the first, In-containing precursor films were sprayed on Mo-coated glass substrates and converted by rapid thermal processing (RTP) to In2Se3. Then a Cu-containing film was sprayed down on top of the In2Se3 and the stacked films were again thermally processed to give CIS. In the second approach, the Cu-, In-, and Ga-containing inks were combined in the proper ratio to produce a mixed Cu-In-Ga ink that was sprayed on substrates and thermally processed to give CIGS films directly. For CdTe deposition, ink consisting of CdTe nanoparticles dispersed in methanol was prepared and used to spray precursor films. Annealing these precursor films in the presence of CdCl2 produced large-grained CdTe films. The films were characterized by x-ray diffraction (XRD) and scanning electron microscopy (SEM). Optimized spray and processing conditions are crucial to obtain dense, crystalline films.

Direct-write contacts: Metallization and contact formation

Using direct-write approaches in photovoltaics for metallization and contact formation can significantly reduce the cost per watt of producing photovoltaic devices. Inks have been developed for various materials, such as Ag, Cu, Ni and Al, which can be used to inkjet print metallizations for various kinds of photovoltaic devices. Use of these inks results in metallization with resistivities close to those of bulk materials. By means of inkjet printing a metallization grid can be printed with better resolution, i.e. smaller lines, than screen-printing. Also inks have been developed to deposit transparent conductive oxide films by means of ultrasonic spraying.

Inkjet printed contacts for use in photovoltaics

Using direct-write approaches in photovoltaics for metallization and contact formation can significantly reduce the cost per watt of producing photovoltaic devices. Inks have been developed for various materials, such as Ag, Cu, Ni and Al, which can be used to inkjet print metallizations for various kinds of photovoltaic devices. Use of these inks results in metallization with resistivity close to those of bulk materials. By means of inkjet printing a metallization grid can be printed with better resolution, i.e. smaller lines, than screen-printing. For metallization on top of silicon photovoltaics also an ink has been developed that will facilitate the burn-through of the contact through the anti-reflection coating. Using this burn-through material may reduce the firing temperature by more than 100°C compared to conventional contact technology.