Solar Energy Conversion Materials by Design...........................................................
Materials play a key role in various aspects of solar energy conversion. Presently available
materials are generally deficient in performance, cost, stability, or some combination thereof.
New materials systems, guided by the interplay between rational design, high-throughput
screening, and theory, are needed to improve the performance of light absorbers, photovoltaic
materials and photoelectrodes, catalysts, thermoelectrics, and infrastructural aspects of solar
energy conversion systems.
EXECUTIVE SUMMARY
Materials play a key role in solar energy conversion to electricity, fuels, and heat. Materials used
in photovoltaics have traditionally been derived from research and development advances in
other technology fields (e.g., Si from microelectronics industry, GaAs from optoelectronics
industry), and as a result, the range of materials currently available for use in photovoltaics is
highly limited compared to the enormous number of semiconductor materials that can in
principle be synthesized for use in photovoltaics. Similarly, high-efficiency thermoelectric and
thermophotovoltaic converters coupled to solar concentrators have the potential to generate
electricity at converter efficiencies from 25 to 35%. Significant progress has been made in these
areas over the last decade, particularly by exploiting nanoscience and nanotechnology. Further
fundamental research can lead to cost-effective materials that enable efficient solar-thermal
energy utilization systems, by developing thermoelectric materials with ZT up to 4, selective
thermal emitters that can withstand >1,000°C, high thermal conductivity polymer-based
materials, and new photovoltaic absorbers and transparent conductors. In order to identify
materials that are ideally suited to solar energy conversion and storage applications, new
experimental and theoretical methods are required that can rapidly assess and select promising
materials from a very large number of candidates. Moreover, the materials selection principle
should be the desire to first optimize a particular material property for use in a device, and
subsequently search among all possible materials for a few specific candidates based on
property-driven selection criteria. Thus, both experimental methods for high-throughput
screening of materials and theoretical methods that identify electronic and atomic structure based
on targeted material properties are needed. Solar concentrators and hot water heaters call for new
low-cost polymer-based materials/composites, while new solar thermal storage materials are
required for several solar thermal conversion applications.
RESEARCH DIRECTIONS
Solar Photon Converters
The traditional approach to development of new materials for application in photovoltaics has
been to identify materials developed for other technological purposes and assess their suitability
to adaptation in photovoltaics. Thus, the materials themselves were developed for other
purposes, and their development often follows the basic sequence in which (1) an interesting
property is discovered; (2) a useful application is invented; (3) “basic research” starts; and
(4) development occurs until the material is of adequate quality for the identified application.