May 11-12, 2010

Denver Airport Marriott at
  Gateway Park
16455 E. 40th Circle
Aurora, Colorado 80011
Ph. 303-371-4333




Background

The National Institute of Standards and Technology (NIST) is conducting a broad-based effort to identify the technical challenges in the development of advanced solar photovoltaic (PV) technologies. Advances in solar PV technologies will lead to significant reductions in cost and improvements in performance, enabling a wider spectrum of energy applications to be addressed. In addition to advances in existing technologies that form the basis for commercial manufacturing, advances are also being made in emerging materials and device technologies. Innovative concepts in thin films, multi-junction, and quantum structures could enable paradigm shifts in PV, but will require considerably more research and development. We believe that this development can be accelerated through progress in measurement science.

The workshop discussion was framed as follows:

The workshop objective is to gain input from photovoltaic experts on the key technical challenges and the role of measurement science in finding solutions, focusing on the following topics:

In addition to the quantum-structured PV applications covered under Excitonics, nanoscience and technology will be a potential cross-cutting issue for discussion in other breakout sessions. These will likely emphasize applications where the nanoscale phenomena are secondary to device physics (e.g., light capture, contacts). Advances in nanotechnology have many applications in the PV industry that could increase performance, among other benefits. Two primary cross-cutting approaches are likely: (1) semiconductor quantum structures, such as quantum dots and wells, which may be embedded/incorporated into traditional semiconductor systems (in particular, thin Si and III-V’s) to tailor and enhance their performance; and (2) nano-engineered structures, such as carbon nanotubes and nanowires which may also be integrated into contacts and other non-semiconductor components. The use of nano-engineered structures allows one to tune / expand the spectral response, enhance the local fields, excite multiple excitons from a single photon, or upconvert infrared photons, thus providing possible routes individually or in combination toward substantial (revolutionary) gains in PCE.

Wafer-based Crystalline Silicon PV
Although crystalline silicon holds as much as 85% of the current PV market, additional research is needed into further reduce costs through increasing efficiency, improving manufacturing yield, enhancing module encapsulation, and other approaches. Advanced measurement tools and techniques are required in all of these areas.

Amorphous Silicon and Polycrystalline Thin Film PV
Opportunities exist for further improvement to the main technologies in this grouping: CdTe, multi-junction thin film silicon, and CIGS. Challenges in these technologies include using thinner absorber and window layers, developing higher rate and atmospheric pressure deposition techniques, improving uniformity and control of stoichiometry over large areas, designing new multijunctions, narrowing the gaps between cell and module PCEs, identifying stability issues (from materials to contacts, and water ingress), addressing materials availability/cost issues, environmental concerns, recycling, understanding interfaces and grain boundaries, and manufacturing process and efficiency improvements.

III-V Multi-Junction PV
While these technologies provide some of the highest efficiencies, many core technological challenges still exist, some related to the extreme illumination conditions and others related to concentrators. Challenges include non-uniform illumination, localized heating, solar spectrum modification, current matching for different solar spectra, series resistance, and materials and device fatigue/reliability.

Excitonic and Quantum-Structured PV
This session includes discussion of solar cells whose absorber layers rely on quantum physics (i.e., confined excitons). At least three different excitonic and quantum-structured solar cell technologies are currently being explored: organic-based, dye-sensitized, and quantum dot/wire technologies. Such solar cells exhibit laboratory PCEs of up to 11%. Numerous challenges exist, both fundamental and technological, to achieving broader commercialization. These include a fundamental understanding of the complex microstructure, photophysical processes, charge separation, charge transport, electronic structure/trapping, contacts and series resistance, spectral matching, and materials and device stability. Other technological challenges include development of processing-property relationships among the molecular structure / microstructure / device performance, and the lack of existing manufacturing base / infrastructure and data on long-term reliability. In general, there is a lack of theoretical models on all levels from device physics to materials processing.