Effect of dye complex structure on performance in DSSCs; An experimental and theoretical study

Use of cobalt-complexes as dye in dye sensitized solar cells (DSSCs) has been a viable contender in the field of photovoltaics due to their low cost, easy production, and wide availability of sources. In this study, we investigated the effect of succinic acid (suc), 1,10-phenanthroline (phen), and benzene-1,3,5-tricarboxylate (BTC) as ligand in metals complex sensitizers with these general formulas: (1) [Co(suc)](n), (2) [Co(2)(suc)(2)(phen)(2)], (3) [Co(3)(BTC)(2)(H(2)O)(n)](n), and (4) [Co(HBTC) (phen) (H(2)O)(2)]; for DSSCs. The bandgap, and energy levels have an important role in photoelectron emission during photovoltaic processes. The bandgap, and energy levels of these dyes (1–4) were estimated by Ultraviolet-Visible (UV-Vis), spectroscopies, and cyclic voltammetry (CV). Delocalized π-electron of phenanthroline in two compounds (2, 4) by effectively reducing band gap energies leads to power conversion efficiency (PCE) of 0.511%, and 1.006%, respectively. Their PCEs to compounds (1, 3) showed an approximate increase of 60%, and 31%, respectively. Furthermore, BTC ligands by more coordinated carboxylate groups in contrast with succinic molecules due to binding sites with TiO(2) cause further enhancement in the efficiency for compounds (3, 4) in contrast with compounds (1, 2). Reasonable agreement is found between experimental and theoretical values calculated using density functional theory (DFT) for the bandgaps and energy levels.