Microreactor-Assisted Nanomaterial Deposition for Photovoltaic Thin Film Production

Technical Objectives

Among the various renewable energy sources, the conversion of sunlight directly into electricity using the photovoltaic (PV) properties of suitable materials is an increasingly attractive option. As a result, the solar PV market is growing at roughly 40 percent per year. However, current PV manufacturing practices suffer from poor energy efficiency and large carbon footprints due to poor material utilization, high processing temperatures and/or high solvent usage. The key enabler for moving PV technology forward is to develop more energy- and material-efficient manufacturing processes for greener, low-cost production of solar cells.

A team of researchers at the Microproducts Breakthrough Institute aims to address this barrier by developing improved processes for the production of nanoscale materials relevant to PV devices. The project will involve improved synthesis, purification, surface functionalization and surface deposition, as well as integration of nanomaterials into composite devices.

To achieve this goal, the researchers are utilizing Microreactor-Assisted Nanomaterial Deposition (MANDTM) and Supercritical Fluid (ScF) technologies. Successful demonstration and commercialization of these technologies could significantly reduce the environmental discharge, manufacturing energy and production costs of current nano-scale thin-film PV manufacturing approaches.

The main objective of this project is to develop and demonstrate a scalable microreactor-assisted nanomaterial deposition pilot platform for the production, purification, functionalization and solution deposition of nanomaterials for PV applications. Phase I of the project focuses on improvement of process unit operations and devices for PV material production. Efforts will target scale-up of the microreactor-assisted deposition of PV nanofilms, as well as the synthesis and purification of PV quantum dot nanoparticles. Phase II of the project will integrate the modular efforts in Phase I to scale-up the microreactor-assisted deposition of PV nanoparticles.

Results to Date

For Generation II solar cell applications, the team has developed recipes and techniques for the production and deposition of CdS thin films on relevant substrates, such as FTO-coated glass plates. This work has progressed from small-scale coupon depositions to larger formats, eventually to culminate in the semi-automated demonstration of thin film deposition on 6-inch substrates—a demonstration of nanomanufacturing as applied to thin film solar cells. Results for small-scale coupons are shown in Figures 1 and 2. The team is currently working on the scale-up of this same technology to a 6-inch platform.

For Generation III solar cells (those enabled by nanocrystals, or quantum dots), the team is developing methods for the production, purification, ligand exchange, solubilization and deposition of target quantum dots on relevant substrates such as TiO2. For instance, Figures 3, 4, and 5 show the results of SnTe quantum dot production from a continuous flow microreactor. Figure 3 shows the ability to control particle shape from sphere to rod. Figure 4 shows the elemental analysis of the materials by EDS, showing a 1:1 relationship between Sn and Te. Figure 5 shows the XRD results for the material, indicating excellent crystallinity.

Implications

Implementation of the project technology would result in both direct and indirect energy, environmental and economic benefits. Direct benefits are seen in the cleaner, more efficient production of PV systems. Very large indirect benefits are seen in the implementation of PV projects, resulting in the displacement of fossil sources of electricity.

The project technology would also reduce chemical waste due to increased material yield, increase productivity due to reduced labor costs and reduced processing time for PV device production and improve material and energy efficiency during the PV device manufacturing process. Estimates indicate MAND-based PV production could save over 16 trillion Btu and reduce carbon emissions by 0.29 million metric tons of carbon equivalent (MMTCE) annually by 2015.

Initial application of the proposed processes will be for improved PV devices that are dependent on nanoscale materials. More broadly, the manufacturing technology (and associated energy savings and waste reduction) developed in this project will be adaptable/applicable to the production of other nanoscale materials and to the devices that use them.

Collaborators

• Daniel R. Palo, PNNL
• R. Shane Addleman, PNNL
• Chih-hung Chang, OSU
• Brian K. Paul, OSU
• Michael O’Halloran, CH2M HILL
• David Schut, Voxtel, Inc.
• Thomas Novet, Voxtel, Inc.

Acknowledgments

This project is primarily funded by the US Department of Energy’s Office of Energy Efficiency and Renewable Energy, through the Industrial Technologies Program under DOE Operating contract DE-AC05-76RL-01830. Additional cash and in-kind cost matching is provided by the Oregon Nanoscience and Microtechnologies Institute, CH2M HILL, Voxtel and Oregon State University.

For Additional Information

Contact the Program Manager Daniel R. Palo.