Recent advances in copper complexes for electrical/light energy conversion

A great deal of research effort has been put in green energy applications in the past few decades based on organic optoelectronics. Compared with conventional inorganic semiconductors, organic counterparts offer a much simpler strategy for low-cost mass production and structural modification. Hence, continuous and intensive academic and industrial research works have been done in these areas. In terms of the materials used, transition-metal complexes with the unique features of the transition metal centers represent a large group of candidates, showing high performance in energy conversion technologies. However, the commonly used transition metals, like Pt(II), Ir(III) and Ru(II), are expensive and of relatively low abundance. Concerning elemental sustainability and marketability, some abundant and cheaper metals should be investigated and further developed to replace these precious metals. Cu(I) complexes have shown their potentiality in solar energy harvesting and light emitting applications, due to their well-studied photophysics and structural diversity. In addition, copper is one of the earth-abundant metals with less toxicity, which makes it competitive to precious transition metals. As a result, a series of rational molecular engineering has been developed to boost the device performance of copper complexes. In this review, the recent progress of copper complexes in the fields of organic light emitting devices (OLEDs), photovoltaic cells (dye-sensitized solar cells (DSSCs) and bulk heterojunction solar cells (BHJSCs)) in the past two decades will be presented. Representative examples are chosen for discussion.