Shuqiang Yang

Nanostructured solar cell

Publisher Summary nThis chapter addresses the nanostructured solar cells that play an important role in enhancing the efficiency of future generations of solar cells, whether they are III–V, II–VI, or hybrid organic–inorganic cells. There is a great deal of potential in multiple approaches for these nanostructures. Nanostructures can also be composed of arrays of individual nanomaterials. Semiconducting quantum dots (QDs) can be combined in a three-dimensional array, often through the use of selfordering. The discrete-like energy levels of the QDs will combine and form bands of allowed energy states in an analogous way in which atomic energy levels combine to produce the energy bands in conventional solids. The role of a nanomaterial or nanostructure in a given photovoltaic solar cell design can vary dramatically. In some cases, the goal may be simply to provide the means to disassociate excitons throughout a bulk material as in the use of colloidal QDs in organic or polymeric solar cells.

High-performance wire-grid polarizers using jet and Flash™ imprint lithography

Abstract. Extremely large-area roll-to-roll (R2R) manufacturing on flexible substrates is ubiquitous for applications such as paper and plastic processing. It combines the benefits of high speed and inexpensive substrates to deliver a commodity product at low cost. The challenge is to extend this approach to the realm of nanopatterning and realize similar benefits. In order to achieve low-cost nanopatterning, it is imperative to move toward high-speed imprinting, less complex tools, near zero waste of consumables, and low-cost substrates. We have developed a roll-based J-FIL process and applied it to a technology demonstrator tool, the LithoFlex 100, to fabricate large-area flexible bilayer wire-grid polarizers (WGPs) and high-performance WGPs on rigid glass substrates. Extinction ratios of better than 10,000 are obtained for the glass-based WGPs. Two simulation packages are also employed to understand the effects of pitch, aluminum thickness, and pattern defectivity on the optical performance of the WGP devices. It is determined that the WGPs can be influenced by both clear and opaque defects in the gratings; however, the defect densities are relaxed relative to the requirements of a high-density semiconductor device.

Enhanced photocurrent in thin-film amorphous silicon solar cells via shape controlled three-dimensional nanostructures

In this paper, we have explored manufacturable approaches to sub-wavelength controlled three-dimensional (3D) nano-patterns with the goal of significantly enhancing the photocurrent in amorphous silicon solar cells. Here we demonstrate efficiency enhancement of about 50% over typical flat a-Si thin-film solar cells, and report an enhancement of 20% in optical absorption over Asahi textured glass by fabricating sub-wavelength nano-patterned a-Si on glass substrates. External quantum efficiency showed superior results for the 3D nano-patterned thin-film solar cells due to enhancement of broadband optical absorption. The results further indicate that this enhanced light trapping is achieved with minimal parasitic absorption losses in the deposited transparent conductive oxide for the nano-patterned substrate thin-film amorphous silicon solar cell configuration. Optical simulations are in good agreement with experimental results, and also show a significant enhancement in optical absorption, quantum efficiency and photocurrent.

High-volume nanoscale imprinting

The ability to pattern materials at the nanoscale enables a variety of applications ranging from high-density data storage, displays, photonic devices, and CMOS integrated circuits to emerging applications in the biomedical and energy sectors. These applications require varying levels of pattern control, shortand long-range order, and have different cost tolerances. Extremely large-area roll-to-roll manufacturing on flexible substrates is ubiquitous for applications such as paper and plastic processing.1–3 It combines the benefits of high speed and inexpensive substrates to deliver an affordable commodity product. The challenge is to extend this approach to the realm of nanopatterning and realize similar benefits. The cost of manufacturing is typically driven by speed (or throughput), tool complexity, price of consumables (materials used, mold or master, and so forth) and substrates, and the downstream processing required (e.g., annealing, deposition, and etching). To make nanopatterning practical, it is imperative to move toward high-speed imprinting, less complex tools, near-zero waste of consumables, and low-cost substrates. Unlike common imprint technologies that rely on heat embossing to melt thermoplastic solids, Jet and Flash Imprint Lithography (J-FILTM/ uses inkjet dispensing of UV-curable resists to assist high-resolution patterning for subsequent dry etch pattern transfer.4–6 The technology is actively being used to develop solutions for memory markets, including flash memory and patterned media for hard disk drives. We have developed a roll-based J-FIL process to fabricate flexible bilayer ‘wire grid’ polarizers (WGPs) and high-performance WGPs on rigid glass substrates, and demonstrated it with a prototype we have named the LithoFlex 100: see Figure 1. The LithoFlex 100 has allowed us to explore the features of an inkjet-resist-driven nanoimprinter. The system uses a 150mm Figure 1. Left: Our ‘technology demonstrator,’ LithoFlex100, being used to develop roll-to-roll inkjet-resist-driven nanoimprinting. Right: The imprint tool enclosed within an environment control unit.

High volume nanoscale roll-based imprinting using jet and flash imprint lithography

Extremely large-area roll-to-roll manufacturing on flexible substrates is ubiquitous for applications such as paper and plastic processing. The challenge is to extend this approach to the realm of nanopatterning and realize similar benefits. Display applications, including liquid crystal (LCD), organic light emitting diode (OLED) and flexible displays are particularly interesting because of the ability to impact multiple levels in the basic display. Of particular interest are the polarizer, DBEF, thin film transistor and color filter; roll-based imprinting has the opportunity to create high performance components within the display while improving the cost of ownership of the panel. Realization of these devices requires both a scalable imprinting technology and tool. In this paper, we introduce a high volume roll-based nanopatterning system, the LithoFlex 350TM. The LithoFlex 350 uses an inkjet based imprinting process similar to the technology demonstrator tool, the LithoFlex 100, introduced in 2012. The width of the web is 350mm and patterning width is 300mm. The system can be configured either for Plate-to-Roll (P2R) imprinting (in which a rigid template is used to pattern the flexible web material) or for Roll-to-Plate imprinting (R2P) (in which a web based template is used to pattern either wafers or panels). Also described in this paper are improvements to wire grid polarizer devices. By optimizing the deposition, patterning and etch processes, we have been able to create working WGPs with transmittance and extinction ratios as high as 44% and 50,000, respectively.