Simulation studies of the characteristics of nitrogen-containing additive molecules for solar cells

Dye-sensitized solar cells (DSSC) are of great scientific significance and application prospect and have attracted wide public concern since they were first reported. The charge recombination in the interface of the DSSC nanocrystalline electrode is thought as a critical issue affecting the DSSC's performance improvement; however, few systematic studies have been carried out to investigate the effect of the electrolyte additives on the charge recombination suppressing. It is reported that the electrolyte additives can enhance the DSSC short-circuit current. In this work, five typical nitrogen-containing six-element heterocyclic additives used in DSSC were researched theoretically at the B3LYP/6-311G** computational level to elucidate the effects of electrolyte additives on DSSC performance. The five additives were pyridine, pyridazine, pyrimidine, pyrazine and 1,3,5-triazine named as A1-A5, respectively. Their molecular properties, some of which are molecule structures, geometrical configurations, dipole moments, charge distributions, vibrational frequencies and frontier orbitals, were calculated and discussed and their effects on DSSC performance were analyzed theoretically. The results showed an enhanced conjugation effect with the increased number of nitrogen atoms in the conjugated rings of A1-A5 molecules and A1-A5 molecules could bond stably onto the electrode surfaces through the coordination bonding of the N atoms. For the electrolyte additives A1-A5-based DSSC devices, open-circuit voltages and light-to-energy conversion efficiencies increased. This work can be helpful to explain the mechanism of charge recombination suppressing of electrolyte additives for DSSC and offers the potential for future development of high-performance DSSC.