Near-infrared Materials: The Turning Point of Organic Photovoltaics.

Near-infrared (NIR) absorbing organic semiconductors have opened up many exciting opportunities for organic photovoltaics (OPVs) research. For example, new chemistries and synthetical methodologies have been developed; single junction solar cell efficiency has been improved from less than 5% to around 19%; novel device architectures such as tandem and transparent organic photovoltaics (TOPV) have been realized. The concept of NIR donors/acceptors thus became a turning point in the OPV field. In this article, we review the development of NIR absorbing materials for OPVs. According to the low-energy absorption window, here we classify NIR photovoltaic materials (p-type (polymers) and n-type (fullerene and non-fullerene)) into four categories: 700-800 nm, 800-900 nm, 900-1000 nm, and greater than 1000 nm. Each sub-section will cover the design, synthesis, and utilization of various types of donor (D) and acceptor (A) units. The structure-property relationship between various kinds of D, A units and absorption window will be constructed to satisfy requirements for different applications. Subsequently, we present a variety of applications realized by NIR materials, including transparent OPVs, tandem OPVs, photodetectors. Finally, we discuss challenges and future development of novel NIR materials for the next-generation organic photovoltaics and beyond. This article is protected by copyright. All rights reserved.