Research On Carbazole-based Dyes In Dye-sensitized Solar Cells

Two triazatruxene（TAT）-based D-π-A’-π-A organic dyes LS101 and LS102 were synthesized.The difference between the two is that the auxiliary acceptors are benzo[c][1,2,5]thiadiazole（BT）and difluorobenzo[c][1,2,5]thiadiazole（DFBT）,respectively.Compared with the electron-withdrawing induction effect of fluorine atoms,the conjugation effect of electron donation is dominant,so the electron-withdrawing ability of DFBT is weaker than that of BT,and the maximum absorption wavelength of dye LS102 is blue-shifted.In addition,the dye loading capacity of LS102 is also weaker than that of LS101.The lower short-circuit current density of LS102 is mainly due to the above two factors.The larger recombination resistance,chemical capacitance and longer electron lifetime also explain the higher open circuit voltage of LS101.In the Co²⁺/Co³⁺electrolyte system,the LS101-sensitized DSSCs achieved a photoelectric conversion efficiency of 10.2%(J_sc=15.1mA cm^-2,V_oc=966 mV,FF=70.1%),while the LS102-based device achieved 8.6%(J_sc=13.4 mA cm^-2,V_oc=934 mV,FF=69.1%).On the basis of the above research,the TAT donor was replaced with triphenylamine（TPA）to synthesize a new organic dye LS103.As a result,it was found that the dye LS101obtained a wider spectral response range than LS103 due to the stronger electron donating ability of TAT.The flatness and structural rigidity of LS101 molecule are also better than LS103,so the higher electron injection efficiency is obtained.In the case of no significant difference in molar extinction coefficient and dye loading capacity,J_sc of dye LS103 is lower.The presence of long alkyl chains in the dye LS101 makes up for its disadvantage of molecular planarity in inhibiting electron recombination.When LS101 is adsorbed on the surface,the Fermi level of TiO₂ shows a greater degree of negative shift.Therefore,the V_oc of LS101 is also higher than that of LS103.Finally,the optimal efficiency of DSSCs with dye LS103 was only 8.1%(J_sc=12.1 mA cm^-2,V_oc=910 mV,FF=73.4%).In addition,the effect of adding co-adsorbent CDCA to the dye LS103 was also investigated.It was found that CDCA did not show obvious ability to inhibit electron recombination,but caused serious competitive adsorption,resulting in reduction in the photocurrent and PCE.