Efficient co-sensitization of novel trimethoxybenzene-based dyes with N-719 for highly efficient dye-sensitized solar cells

Abstract

Five novel metal free organic dyes (AL1-5) have been designed and synthesized as sensitizers/co-sensitizers for dye sensitized solar cells (DSSCs). Theoretical, electrochemical, photophysical and photovoltaic performance properties of the target molecules with respect to their chemical nature were investigated. Compared to other dyes (AL1, AL2, AL4, and AL5), DSSC based on sensitizer AL3 outperformed other dyes in photovoltaic performance, as shown by JSC = 8.28 mA cm−2, VOC = 623 mV, and power conversion efficiency (PCE) = 3.07%. This could be attributed to improved charge transfer of AL3 from donor to acceptor, leading to increased photocurrent (JSC). Consequently, dye AL3 has showcased the highest PCE (9.44%) as a co-sensitizer along with the standard Ru(II) dye (N-719). The N-719 based cells employing AL1-5 as co-sensitizers yielded the PCE of 6.31, 8.42, 9.44, 6.37 and 7.55%, respectively, while N-719 alone displayed 8.12%. Electrochemical impedance spectroscopy analysis showed that the fabricated device (N-719 + AL3) has much lower charge transfer resistance than other devices confirming its highest photovoltage value of 715 mV. Density functional theory (DFT) calculations were performed to theoretically characterize the optical and electrochemical properties of the synthesized dyes. These findings clearly support the role of sensitizer/co-sensitizer molecular structures in the operating performance of DSSCs.