Dr. Gang Li, Ph.D.
Organic photovoltaic (OPV) devices are promising for low-cost, flexible, lightweight, large-area energy generation applications. Tremendous efforts on designing new materials, device struc-tures, and processing techniques have been carried out in the past decade to improve the pow-er conversion efficiency (PCE). The state-of-art polymeric OPV cells have achieved over 9% PCE using a single junction bulk heterojunction (BHJ) device structure. To go beyond the theo-retical barrier for single junction OPV, an effective approach is to stack multiple photoactive layers with complementary absorption spectra to form tandem PSC. Compared to a single-junction device, the structure reduces photovoltage loss during the photovoltaic process, be-cause the open-circuit voltage (VOC) from a solar cell is fundamentally limited by the bandgap of the active materials. Recently we demonstrated a highly efficient tandem PSC with a novel low-bandgap conjugated polymer (bandgap~1.44 eV) specifically suitable for tandem structure and a NREL certified 8.62% was reached. It was soon surpassed by a new record of NREL certified 10.61% PCE through progress in new polymer and device architecture. In this talk, we will dis-cuss the key progresses in UCLA which eventually lead to the over 10% solar cell performance, including morphology, interface engineering, material and device architecture innovation. The propose routes towards 15% and beyond OPV efficiency will be discussed.
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