Browsing by Author "Chang, Sheng-Yung"

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Efficient Tandem Organic Photovoltaics with Tunable Rear Sub-cells
(2019-02-20)
Cheng, Pei
;
Liu, Yuqiang
;
Chang, Sheng-Yung
;
Li, Tengfei
;
Sun, Pengyu
A tandem structure was invented to enhance photon utilization efficiency and reduce thermal loss. Considering the unique advantages of non-fullerene acceptors (NFAs), the combination of NFAs and the tandem concept shows great potential for organic photovoltaics (OPVs). Herein, a simple strategy to balance the voltage-current trade-off in tandem OPVs by employing mixed NFAs in rear sub-cells is reported. The V-OC and J(SC) of rear sub-cells can be tuned by using the blend of donor/NFA/NFA. This strategy offers an easy approach to balance the V-OC and J(SC) in tandem OPVs toward higher power conversion efficiency (PCE) without rational and careful synthesis of new materials. Tandem OPVs based on mixed NFAs in rear sub-cells exhibited the best PCE of 13.3% in the lab. Importantly, the tandem devices were certified by the National Renewable Energy Laboratory (NREL) under asymptotic scans, and a PCE of 11.52% was achieved and recognized on the most recent NREL chart.
High-Efficiency Organic Tandem Solar Cells With Effective Transition Metal Chelates Interconnecting Layer
(2017-10-01)
Chang, Sheng-Yung
;
Lin, Yu-Che
;
Sun, Pengyu
;
Hsieh, Yao-Tsung
;
Meng, Lei
Organic tandem solar cells have two sub-cells vertically connected via a tunnel junction (or interconnecting layer, ICL), which the ICL plays a critical role of determining the performance of the tandem cell. In this manuscript, we report a new design of the ICL consisting of zirconium (IV) acetylacetonate (Zr-Acac) as the electron transport layer. The Zr-Acac has a suitable work function to pin the Fermi-level of the ICL and hence, can effectively behave as the charge recombination function for the tandem device. Comparing to the reference device consisting of ZnO ETL layer, the Zr-Acac ICL can effectively enhance the efficiency by 20%, from 8.4 to 10.1% power conversion efficiencies. More importantly, the Zr-Acac ETL layer functions effectively without thermal annealing, which not only simplifies the tandem solar cell processing, but also widens the front sub-cell material selection.
Unraveling Sunlight by Transparent Organic Semiconductors toward Photovoltaic and Photosynthesis
(2019-02-01)
Liu, Yugiang
;
Cheng, Pei
;
Li, Tengfei
;
Wang, Rui
;
Li, Yaowen
Because the visible and the infrared (IR) regions take up similar to 47% and similar to 51% of the energy in the solar spectrum (AM 1.5G standard), respectively, utilizing the visible light for plant growth and the IR light for power generation is potentially extremely exciting. IR-absorbing organic semiconductors, with localized IR absorption and visible-light transmittance, would be promising materials for this purpose. Here, flexible transparent organic photovoltaics (TOPVs) based on IR-absorbing organic materials were proposed, which can be a simple, low-cost, and promising way to utilize the IR light for electricity generation, and the penetrated visible light will be utilized for photosynthesis in plants. A power-conversion efficiency of similar to 10% with an average visible transmittance of 34% was achieved for TOPV devices. Meanwhile, the side-by-side comparison showed that plants grown under the TOPVs filtered light, and those under normal sunlight yielded very similar results. These outcomes demonstrated the results from TOPV devices beyond simple photovoltaic applications.