Molecular modifications in fluorene core for efficient organic photovoltaic cells

The upgraded version of solar cells is organic photovoltaic (OPV) device. Substantial efforts have been made in development of new light sensitive materials (donor, acceptors and hole transport materials etc.), and further modification in different units of these materials and device fabrication process to achieve better performance in OSCs. Fluorene is a fluorescent, poor electron providing polycyclic aromatic molecule shows absorption from 220 to 310 nm with lambda max of 329 nm and deep lying HOMO energy level which is favorable to gain high value of open circuit voltage (Voc) of fluorene based materials. Several acceptor materials have been synthesized by using fluorene as a building block for solution processable organic photovoltaics (OPVs). A variety of climatic type fluorene based NFAs by placing different donor (D) and acceptor (A) units with a structural arrangement of A-D/ A-D-D/A-A were explored for OPV cells. Further several modifications in molecular backbone of the acceptors were performed by modifying central donor such as fluorene, spiro fluorene and fluorene unit fused with other aromatic ring and by revamping at pi-bridge, terminal units and alkyl side chain to enhance the power generation efficiency of solar cells. This review for the most part focuses on encapsulating the simple fluorene and its derivatives core based small molecule NFAs based.