Revealing the photophysics of N719 dye based dye-sensitized solar cell

Dye-sensitized solar cell (DSSC) has demonstrated promising photovoltaic performance with several photo-sensitizers. N719 dye, is a popular sensitizer used in DSSC due to its ability to absorb light in the visible region and its unique characteristics such as ultrafast electron injection and stable anchoring to the TiO2 surface. However, many of its intriguing optoelectronic properties and charge carrier relaxation at low frequency are contested. Here impedance and modulus spectroscopy were employed to extensively explore the charge carrier dynamics under both light-off and illumination conditions, and it was found that there is a significant change observed in the low-frequency regime in both cases. The fabricated N719 dye based DSSC exhibit the highest JSC of 10.89 mA/cm2, a highest VOC of 0.672 V, a fill-factor of 0.65 and photoconversion efficiency of 4.81%. The Nyquist plot of N719 DSSC under light-off and illumination conditions demonstrates that at higher frequency, a small arc is observed, and at a lower value, a large arc is observed. Moreover, the Nyquist plots exhibit depressed semicircles due to deviation from ideal Debye relaxation nature. The dielectric relaxation is found to follow the interfacial polarization of Maxwell-Wagner type probably attributed to the grain boundary effects. Furthermore, the comparative analysis of modulus and impedance spectra at low frequency reveals the localized carrier relaxation in this N719 DSSC which has been correlated with conductivity hopping process.