Salleo Group:

The Salleo group's research focuses on novel materials and processing technologies for large-area and flexible electronic/photonic devices.

Organic Semiconductor Microstructure and Charge Transport

Organic semiconductors have garnered significant interest in recent years for applications in large-area, low-cost, and flexible electronics. These materials can be processed from solution and are compatible with inexpensive and high-throughput printing and coating deposition techniques. We are interested in structure/property relationships in these materials, and use an array of techniques to characterize the structural, optoelectronic, and electrical properties of polymer and small molecule thin films. Our group has special expertise in synchrotron-based X-ray diffraction techniques and we conduct many experiments at the Stanford Linear Accelerator Center (SLAC). Fabrication of nano-scale devices is also used to characterize fundamental transport processes in these materials.

a) Polarized microscope image and b) phase mode AFM image of directionally crystallized P3HT.

Upconverting Nanoparticles

Although recent innovations in cell architecture and fabrication techniques have yielded substantial improvements, the efficiencies of single-junction solar cells remain fundamentally limited by transmission of sub-band gap photons. Photon upconversion represents a promising approach toward overcoming this efficiency limit; by absorbing sub-band gap light and upconverting it to energies above the solar cell's band gap, an upconverting layer can significantly boost the efficiency of any single-junction cell by enabling it to utilize photons it would otherwise waste. Our group is actively exploring routes to boost the efficiency of upconverting systems and elevate the technology from a largely academic pursuit to a commercial breakthrough.

a) Schematic depicting proposed device architecture. (b) Dispersion of NaYF4:Er,Yb nanoparticles illuminated with near-infrared light and emitting green light.

Organic Solar Cells

The efficiency of organic solar cells has improved dramatically in recent years, reaching values in excess of 10%. However, many aspects of the internal workings of these devices are still unclear, and there remains significant potential for increasing the efficiency further. Our group studies the mechanisms of charge generation, separation, and transport in these devices, particularly the relationship between microstructure and the efficiency of opto-electronic processes determining the photovoltaic action.

The internal aspects which affect photovoltaic performance in polymer:fullerene solar cells.

Nanoparticle Synthesis

Transparent conducting oxides have gained great industrial importance. Zinc oxide is extensively used as a transparent conductor for optoelectronic applications due to its wide band gap and high conductivity when doped. Precise control of the nanoscale morphology and controllable doping of zinc oxide nanoparticles are active areas of research for colloidally synthesized metal oxide nanocrystals. Realization of anisotropic doped zinc oxide nanocrystals could enable fundamental studies on doping in nanoscale systems as well as new applications in plasmonics. Our group, in collaboration with the Molecular Foundry (LBNL), is developing nanocrystal syntheses for anisotropic zinc oxide nanocrystals and new strategies for doping them.

TEM images and size distributions of colloidally grown zinc oxide nanorods with varying aspect ratios.
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Last Updated:
May 25, 2013