Ladder-Type Heteroarene-Based Organic Semiconductors.

The fusion of heteroaromatic rings into ladder-type heteroarenes can stabilize frontier molecular orbitals and lead to improved physicochemical properties that are beneficial for applications in various optoelectronic devices. Thus, ladder-type heteroarenes, which feature highly planar backbones and well-delocalized π conjugation, have recently emerged as a promising type of organic semiconductor with excellent device performance in organic photovoltaics (OPVs) and organic field-effect transistors (OFETs). In this Focus Review, we summarize the recent advances in ladder-type heteroarene-based organic semiconductors, such as hole- and electron-transporting molecular semiconductors, and fully ladder-type conjugated polymers towards their applications in OPVs and OFETs. The recent use of ladder-type small-molecule acceptor materials has strikingly boosted the power conversion efficiency of fullerene-free solar cells, and selected examples of the latest developments in ladder-type fused-ring electron acceptor materials are also elaborated.