A study on the impact of betalain chemical modification on the efficiency and stability of dye-sensitized solar cells

Abstract

This study investigates the effect of the chemical modification of betalain pigments, extracted from purple Bougainvillea glabra, on the photovoltaic performance of dye-sensitized solar cells (DSSCs). The extraction yield of crude betacyanin from B. glabra was approximately 8.75%. The unmodified betalain (B) and the modified betalain (MB) were used as natural sensitizers; their adsorption behaviors on TiO2 were analyzed and compared. The structural and optical properties of both dyes were characterized using Fourier-transform infrared (FTIR) spectroscopy, proton nuclear magnetic resonance (1H-NMR) spectroscopy, and ultraviolet-visible (UV–Vis) spectroscopy. The chemical modification of the crude betacyanin extract proceeded with a yield of 69.5%. The photovoltaic performance of DSSCs based on B and MB was evaluated under standard solar illumination (100 mW/cm2). The DSSC sensitized with B exhibited a higher power conversion efficiency (PCE) of 0.31% and a short-circuit current density (Jsc) of 2.31 mA/cm2, whereas the DSSC sensitized with MB demonstrated a lower efficiency (0.14%) and Jsc of 0.91 mA/cm2. Despite this decrease in efficiency, a 100-hour stability test showed that DSSCs sensitized with MB retained approximately 73% of their initial efficiency, while those based on B retained only 31%, highlighting a significant improvement in long-term stability. EIS characterization of DSSC based on the two different sensitizers were made. These results suggest that MB-based DSSCs are more durable and potentially more competitive with inorganic-based solar cells. Overall, the findings highlight the trade-off between initial efficiency and long-term stability and provide valuable insights into the development of natural dye-based DSSCs with improved performance.