Molecular design and synthesis of new metal-free organic chromophores for dye sensitized solar cells

Abstract

The quest for neat and cost effective renewable energy has led to added research attention on organic photovoltaics. Over the past two decades, the dye-sensitized solar cell (DSSC), which belongs to the thin film photovoltaic technology, has emerged as an attractive and promising lowcost solar device after the inventive research work reported by Gratzel group. Among the different components of DSSCs, the dye as a photosensitizer plays a crucial role in the process of the cells, which include sunlight harvesting and electron injection from excited dye into the CB edge of TiO2. At present, there is a considerable interest among the researchers to design and develop new n- type organic chromophores for DSSC application. In this context, it was planned to design, synthesize and investigate the photovoltaic performance of new organic dyes based on N, N dimethylaniline (Series-1A, n-C1-5) and carbazole (Series-1B to 5, n-C6-21) as n-type sensitizers/co-sensitizers. In addition, it has been contemplated to design and investigate three new carbazole based dyes (Series-6, p-C1-3) as potential p-type sensitizers for DSSC application. Based on the detailed literature survey, twenty one new n-type organic sensitizers/cosensitizers and three p- type organic sensitizers were designed with various design strategies. They were successfully synthesized following appropriate synthetic protocols. Further, they were wellcharacterized by spectral, optical and electrochemical analyses. Their optical and electrochemical parameters along with molecular geometries were optimized, and DFT has been employed to apprehend the effect of structures of organic sensitizers/co-sensitizers on their photovoltaic performances. Finally, the synthesized dyes were subjected to the photovoltaic studies. Among ntype organic sensitizers, the cell fabricated with n-C13 displayed the optimum PCE of 3.55%. Whereas, the co-sensitization studies, indicated that, under the same conditions, the device cosensitized using n-C6 dye with NCSU-10 sensitizer showcased upheld PCE of 9.55%. Finally, the new three p-type organic dyes were sensitized on NiO and their photovoltaic results revealed that, p-C2 sensitized DSSC exhibited optimum photovoltaic performances which are comparable with that of the bench mark reference P1. To sum up, by appropriately optimizing the molecular structures of metal-free organic dyes, it is possible to further ameliorate the photovoltaic performance of the cells.