Robust hybrid hydrogels with good rectification properties and their application as active materials for dye-sensitized solar cells: Insights from AC impedance spectroscopy

Dihybrid (GP) and trihybrid (GPPS) hydrogels constructed by 5,5′-(1,3,5,7-tetraoxopyrrolo[3,4-f]isoindole-2,6-diyl)diisophthalic acid (P), graphene oxide (GO) and P, GO, and PEDOT:PSS are studied. The gelation occurs through H-bonding and π-π stacking interactions. A magnificent improvement occurs in the mechanical properties of the hybrid gels compared to the P gel. The dc-conductivity of GPPS xerogels is 4-5 orders of magnitude higher compared to the GP and P xerogels. The current-voltage (I-V) characteristic curves of the GP and GPPS gels exhibit rectification properties with the highest rectification ratio of 61; however, the xerogels exhibit semiconducting nature. The GP and GPPS xerogels exhibit photoresponse behavior, and the on-off cycles display a stable photocurrent for the latter system. Dye-sensitized solar cells (DSSCs) are fabricated taking the GPPS gels as active materials and the power conversion efficiency (PCE) increases with the increase of PEDOT:PSS concentration showing a maximum PCE of 4.5%. The IPCE curve shows an absorption range of 360-700 nm with the maximum absorbance of ∼57%. Impedance spectroscopy indicates a considerable difference in the Nyquist plots between the xerogels and gels; the latter exhibit a semicircle with an additional spike corresponding to the Warburg impedance. The Cole-Cole plot of the DSSC consists of three semicircles and the equivalent resistance-capacitance circuits elucidate the PCE values.