July 20, 2011 –  Day 2 of the 3 day Organic Microelectronics & Optoelectronics Workshop VII spent the morning on PV technologies, returning in the afternoon to organic semiconductors. John Benner of NREL opened with an overview of PV economics and technology. Silicon PV is well on its way to $0.70/watt at the module level, but CdTe is still setting the pace for low cost, projected to be under $0.50/W shortly. Alta Devices has a 28.2% cell efficiency on a thin-film device now in pilot production. Multi-band cells are commercially available at >40% efficiency with the ability to fine tune to the local solar spectrum. CPV systems producing 60kW are operating in the field at the 27% system efficiency level, which is a significant milestone for commercialization and capitalization. Installation permit fees are a significant non-technical contributor to the expense of installing systems with any technology.

Jeff Peet of Konarka explained charge carrier recombination in bulk heterojunctions (BHJ) cells. Konarka’s OPV technology is polymer cells cast from sol gel solutions. They’ve opened a new R2R production facility in New Bedford, MA in the old Polaroid plant. One target market is building-integrated semi-transparent OPV window coatings that can be colored and printed with designs. Many of the San Francisco bus stop kiosks have Konarka flex cells mounted on the red kiosk ripple top. Using semiconducting films thicker than 200nm typically leads to a loss of fill factor. A new material (internal label ZZ115) maintains a high fill factor at thicknesses of 200-400nm, which enables a broader flat band for EQE. The material has been shared with NIST and three other collaborators to characterize the material and understand why it works so well.

Decomposition of a high-energy singlet into two low energy triplets was explained by Priya Jadhav of MIT, and elucidated with several device examples. This singlet fission is an example of a multi-exciton generation process that will potentially allow OPV cells to exceed the Shockley-Quiesser limit. An applied magnetic field is found to increase the photocurrent by 5% in a DPT-C₆₀ device and decrease photocurrent in a Tetracene-C₆₀ device.

Moritz Riede of Technische Universit