Recent Developments in Copper and Iron Based Dyes as Light Harvesters

Abstract

Application of transition metal complexes as light harvesters or sensitizers for solar cells is an active research field. Second- and third-row transition metal based sensitizers such as Ru, Ir and Pt have been extensively investigated and Ru-polypyridyl dyes have been reported to be the most efficient. But these metals are very expensive and scarce. This has intensified the investigations for alternative sensitising dyes based on more abundant first-row transition metals such as copper, iron and nickel. However, these metal complexes have excited states with a very short lifetime unlike their second and third row analogues due to which electron injection in the TiO2 layer becomes a limiting factor resulting in lower efficiency. To develop efficient DSSCs, the first-row transition metal sensitizer molecule design should focus simultaneously on optimising their chemical properties to enhance spectral coverage and photo-physical properties to enhance the lifespan of excited states. Recently, theoretical studies of electronic and spectral properties of sensitising dye molecules using Density functional theory have served as an important guide to design sensitizers with improved efficiency. A few complexes of Cu(I) and Fe(II) N-heterocylic carbenes have been reported to have great potential as efficient sensitizers. This paper summarises various strategies adopted by researchers and the efforts devoted to exploring the possibility of using these metal complexes as light harvesters in recent years.