Hole (donor) and electron (acceptor) transporting organic semiconductors for bulk-heterojunction solar cells

The field of bulk heterojunction (BHJ) organic photovoltaics (OPVs) or solar cells (OSCs) has experienced a dramatic advance toward a competitive technology reflecting the introduction of new materials, tuning of materials combinations, and optimization of the device architecture. Thus, binary BHJ OSCs with power conversion efficiencies surpassing 18% have been demonstrated. In this review we discuss recent developments in the area of p-conjugated small-molecule and polymeric semiconductors for organic BHJ-OSCs focusing on both electron-donor (hole-transporting) and electron-acceptor (electrontransporting) semiconductors developed during the past three years. Thus, several families of semiconductor materials including donor-acceptor (D-A) polymers, fullerene, and non-fullerene acceptors (NFAs) are reviewed including their combination for poly mer-fullerene, donor polymer-NFA, all-small molecule, and all-polymer solar cells.