Shawn P. Williams

Polymer–Fullerene Bulk‐Heterojunction Solar Cells

Solution-processed bulk heterojunction organic photovoltaic (OPV) devices have gained serious attention during the last few years and are established as one of the leading next generation photovoltaic technologies for low cost power production. This article reviews the OPV development highlights of the last two decades, and summarizes the key milestones that have brought the technology to todays efficiency performance of over 7%. An outlook is presented on what will be required to drive this young photovoltaic technology towards the next major milestone, a 10% power conversion efficiency, considered by many to represent the efficiency at which OPV can be adopted in wide-spread applications. With first products already entering the market, sufficient lifetime for the intended application becomes more and more critical, and the status of OPV stability as well as the current understanding of degradation mechanisms will be reviewed in the second part of this article.

Advances in Plexcore active layer technology systems for organic photovoltaics: roof-top and accelerated lifetime analysis of high performance organic photovoltaic cells

We report NREL-certified efficiencies and initial lifetime data for organic photovoltaic (OPV) cells based on Plexcore PV photoactive layer and Plexcore HTL-OPV hole transport layer technology. Plexcore PV-F3, a photoactive layer OPV ink, was certified in a single-layer OPV cell at the National Renewable Energy Laboratory (NREL) at 5.4%, which represents the highest official mark for a single-layer organic solar cell. We have fabricated and measured P3HT:PCBM solar cells with a peak efficiency of 4.4% and typical efficiencies of 3 - 4% (internal, NREL-calibrated measurement) with P3HT manufactured at Plextronics by the Grignard Metathesis (GRIM) method. Outdoor and accelerated lifetime testing of these devices is reported. Both Plexcore PV-F3 and P3HT:PCBM-based OPV cells exhibit >750 hours of outdoor roof-top, non-accelerated lifetime with less than 8% loss in initial efficiency for both active layer systems when exposed continuously to the climate of Western Pennsylvania. These devices are continuously being tested to date. Accelerated testing using a high-intensity (1000W) metal-halide lamp affords shorter lifetimes; however, the true acceleration factor is still to be determined.

Efficiency and Stability Investigations of Large Area Organic Photovoltaic Modules

Large area organic photovoltaic modules have been fabricated with 232.8 cm2 of total area with 108 cm2 of photoactive area. Efficiencies up to 2.3% by active area (1.1% by total area) demonstrate operation of a multicell module with configurable voltage and current output. NREL certification is reported and is an example of the largest OPV module certified by NREL, as well as the only polymer:fullerene-based module tested. Module lifetime data were collected and with ca. 550 h of light-soaking, > 2000h of lifetime is expected based on extrapolation. The conditions of the test were 100% duty cycle, ~ 1 Sun Xe-arc lamp, KG5-Si reference, ~25 °C controlled temperature. The lifetime data were normalized with respect to the variations and fade of the Xe-arc lamp source.