Science News: 2021 Advanced Materials, Near-Infrared Materials: A Turning Point in Organic Photovoltaics

  Advanced Materials (IF 30.849) published a study by Yang Yang from University of California Los Angeles (UCLA) et al. in October 2021.  Near-infrared (NIR) absorbing organic semiconductors have opened up many opportunities for organic photovoltaics (OPVs) research, such as the development of new chemistries and synthetical methodologies. In addition, single junction solar cell efficiency has been increased from less than 5% to about 19%; novel device architectures such as tandem and transparent organic photovoltaics (TOPV) have also been realized. Therefore, the concept of NIR donor/acceptor became a turning point. This article mainly reviews the development of NIR absorbing materials for OPV and emphasizes that the intramolecular charge transfer (ICT) effect plays an important role in adjusting the absorption window of organic semiconductors.

The optical absorption window is an important indicator for judging NIR materials.

  According to the low-energy absorption window, the authors classify NIR photovoltaic materials (p-type (polymers) and n-type (fullerene and non-fullerene)) into four categories: 700-800nm, 800-900nm, 900-1000nm and greater than 1000nm. Discuss the design, synthesis and utilization of various types of donor (D) and acceptor (A) units respectively. The structure and performance between the various D and A units and the absorption window are closely connected to meet the needs of different applications.

Invention of NIR OPV
absorption window four categories OPV

According to the low-energy absorption window, the authors classify NIR photovoltaic materials into four categories.

  Due to the absorption capacity and good conductivity of the near-infrared spectrum, NIR materials can expand the absorption range of the spectrum, strengthen the photon capture ability of organic optical devices, and affect the development of organic solar cells (OSC). In the article, various applications of NIR materials are also shown, including:
(1) Transparent/ semitransparent OPVs: They can be applied to portable integrated solar charging devices, power generation roofs and self-powered greenhouses.

(2) Tandem OPVs: The stacked device structure can effectively improve the efficiency of OSC, can utilize a larger range of solar spectrum, and effectively reduce the loss of photons in the form of heat.
(3) Photodetectors: As NIR light has long propagation distance and low attenuation characteristics in biological tissues, it can be used in environmental monitoring, clinical diagnosis, night monitoring, and portable electronic equipment.

  Finally, it discusses the challenges and future development of novel NIR materials for the next-generation of organic photovoltaics and other fields, including the following directions: material design, device engineering, device structure and theoretical calculations.

application of NIR in photodetectors

Application of Near Infrared Light in Photodetectors.

Key Word: near-infrared, organic photovoltaic, organic solar cell

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