liu-et-al-2019-unraveling-sunlight-by-transparent-organic-semiconductors-toward-photovoltaic-and-photosynthesis

Unraveling Sunlight

  • Authors: Yuqiang Liu, Pei Cheng, Tengfei Li, Rui Wang, Yaowen Li, Sheng-Yung Chang, Yuan Zhu, Hao-Wen Cheng, Kung-Hwa Wei, Xiaowei Zhan, Baoquan Sun, Yang Yang.

  • Institutions: University of California Los Angeles, Soochow University, Peking University, National Chiao Tung University.

Abstract

  • The solar spectrum contains ~47% visible light and ~51% infrared (IR) light.

  • Transparent Organic Photovoltaics (TOPVs) can utilize IR for electricity and visible light for photosynthesis.

  • Achieved power-conversion efficiency (PCE) of ~10% with 34% average visible transmittance.

  • Plant growth under TOPV light similar to growth under normal sunlight.

  • KEYWORDS: Infrared light, Transparent, Flexible, Organic Photovoltaic, Photosynthesis.

Introduction

  • IR-absorbing organic semiconductors can be optimized for narrow IR absorption while allowing visible light transmission.

  • Absorption spectrum for photosynthesis (400-700 nm) is outside IR semiconductors' absorption range.

  • Even 10% visible light transparency can suffice for plant growth.

Flexible TOPV Devices

  • Materials: Flexible TOPV devices made from IEICO-4F, F8IC, FOIC with power-conversion efficiencies of 10.02%, 8.92%, and 9.26% respectively.

  • Top structures: PET, Ag mesh, PH 1000, ZnO, various active layers.

  • Schematic showing sunlight absorption for power and transmission for photosynthesis.

  • Notable transmittance properties allow simultaneous power generation and plant growth.

Results and Discussion

  • Plants grown under TOPVs exhibited comparable growth to those under normal sunlight.

  • The devices maintained PCE even when bent at angles up to 60°.

  • External and internal quantum efficiency spectra showed high utilization of visible light.

Performance Data

  • PCE Achievements:

    • PTB7-Th/IEICO-4F: Average PCE 9.66%, JSC 20.27 mA/cm², VOC 0.707 V.

    • PTB7-Th/F8IC: Average PCE 8.69%, JSC 18.97 mA/cm², VOC 0.687 V.

    • PTB7-Th/FOIC: Average PCE 8.86%, JSC 17.82 mA/cm², VOC 0.756 V.

Implications for Agriculture

  • Mung bean growth under TOPVs was slightly slower but ultimately comparable to normal sunlight.

  • Lack of light led to wilting in beans grown without light.

Conclusion

  • TOPVs effectively separate energy use for electricity and photosynthesis without compromising growth.

  • Performance suggests a promising future for transparent photovoltaic applications in agriculture.

Experimental Section

  • Materials: Specific organic materials and fabrication substrates were essential for optimal performance.

  • Fabrication Process: Included PET substrate preparation, coating with various layers, and creating specific structures for light transmission.

Acknowledgments

  • Financial support from various institutions including AFOSR and ONR.