Abstract:

In this presentation, I will firstly introduce the basic principal of photovoltaic (PV) materials and devices.  Once the fundamental aspects have been laid out, I will follow with a detail discussion of organic photovoltaics (OPV) and perovskite (PVSK) PV technologies.

OPV technology, utilized organic and polymer materials as the active elements, which has emerged as one of the promising photovoltaic technologies. One of the features of using organic compounds as active materials is the narrow absorption. Recently, in order to broaden the absorption, we successfully designed an OPV device with three components as the active materials. As a result, power conversion efficiencies (PCEs) of 11-12% were achieved. Very recently, we obtained very high performance single-junction OPV by the synthesis of new infrared absorbing non-fullerene acceptors. These single-junction devices were certified by NREL, and a new record PCE of 12.6% PCE was achieved.

On the other hand, perovskite solar cell is another major research in my group. The characteristic grain boundaries (GBs) of the polycrystalline perovskite films were found to contribute to the trap states and further act as vulnerable spots to trigger environmental degradation. In this presentation, I will report our recent understanding on methods for manipulation of the defects in perovskite solar cells. Crystallization kinetics of the perovskite layer was controlled by engineering of intermediate phases, which resulted in significant enhancement in crystallinity with reduced defects. The inevitable defects at GBs were effectively passivated by additives. Significant enhancement in photoluminescence lifetime supported effective passivation of defects at the perovskite layer. As a result, the PCE exceeding 21% (steady-state PCE of 20.64%) was achieved for a planar heterojunction perovskite solar cell. Thanks to the passivated GBs, the device demonstrated significantly enhanced stability. I will also report our progresses on perovskite tandem solar cells. A high performance perovskite tandem solar cell was achieved via engineering of the interconnecting junction, where certified power conversion efficiency over 22% was demonstrated.

Biography:

Dr. Yang received his Ph.D. in Physics and Applied Physics from University of Massachusetts Lowell in 1992. Prof. Yang’s major researches are in the solar energy field.  He has more than 300 refereed papers; 46 patents (20 issued and 26 pending), and 200 invited talks.  His H-Index is 147 (March 2019). His major contribution in the organic solar energy is in the understanding of polymer morphology and the influence on device performance; the invention of inverted organic solar cell, and inverted tandem solar cell. Yang has created several world record high efficiencies in organic solar cells, including the recent 11.5% and 12.6% certified by NREL (2018). In 2014, his group achieved 19.3% PCE in perovskite solar cells. 20.23% PCE (certified by NREL) of perovskite/CIGS solar cell and 22.4% PCE (certified by NREL) CIGS/Perovskite tandem solar cell of record solar cell. (2018). The Carol and Lawrence E. Tannas Jr. Endowed Chair in Engineering (2011); Top Hot Researcher in 2010, Science Watch (published by Thomason Reuters), only 11 scientists were selected, including Andre Geim, the Nobel Prize Laureate in Physics, 2010; Highly Cited Researchers (Materials Science & Chemistry, Thompson Reuter 2014 - now); Fellows of MRS (2015), American Physical Society, Royal Society of Chemistry (2014), SPIE (2014), and the Electro Magnetics Academy (2014). The most Influential Scientific Mind by by Thomson Reuters (2016), Highly Cited Researchers in Chemistry, Materials Science, and Physics cross-fields (2018), only 23 people were selected.

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