Basic Research Needs for Solar Energy Utilization - Office of ...

MATERIALS ARCHITECTURES FOR SOLAR ENERGY: ASSEMBLING
COMPLEX STRUCTURES
Solar energy conversion devices necessarily involve assembly of nanometer-scale structures into
meter-sized articles of manufacture. At present, relatively few methods exist for arranging matter
cheaply, robustly, and precisely over such a span of length scales. To enable low-cost
fabrication of the large areas of solar energy conversion structures that will be needed if solar
energy is to contribute significantly to the primary energy supply, methods must be developed for
self-assembly and/or bonding of structures over this span of length scales.
EXECUTIVE SUMMARY
Controlling organization of matter across various length scales is critical for inexpensive
fabrication of functionally integrated systems for converting solar photons. Self- and directedassembly
are leading strategies for fabricating such systems. The efficiency of solar cells also
depends critically on the morphology and structure of the active materials across many length
scales — from the nanoscale to the macroscale. New techniques, tools, and design principles are
needed to allow optimized, nanostructured materials and photonic structures to be fabricated
over large-area substrates. These techniques may be based on kinetically and/or
thermodynamically driven self-assembly of tailored building blocks, or alternatively, they may
rely upon construction of the active layers and devices using carefully controlled vapor or
solution-based deposition methods. Such new materials and systems are also expected to
incorporate many of the design principles that operate in biological photosynthetic systems. The
synthetic, photocatalytic materials should allow the spatial arrangements of active components,
and the “traffic control” of chemical reactants, intermediates, electrons, and products. The
ultimate objective of this area of research is to develop low-cost approaches to fabricating the
active materials and components of solar photon conversion systems over large-area substrates.
RESEARCH DIRECTIONS
Develop Scalable Deposition Methods for Organic, Inorganic, and Hybrid Building
Blocks
Currently, organic and hybrid photovoltaic (PV) cells are fabricated using wet and vapor
deposition methods to afford small-area prototype cells. A vigorous research effort is required to
develop new approaches for controlled deposition of a variety of building blocks ranging from
small organic molecules and polymers to nanocrystalline inorganic semiconductors. These new
methods should include novel vapor deposition methods and wet processing techniques,
including spin-, dip- and spray-coating, ink-jet and screen printing, and roll-to-roll processing.
An important caveat is that the novel deposition methods should allow control of the morphology
of the active materials (see next section) and at the same time they need to be scalable to allow
large-area solar cells and modules to be constructed.
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