Effect of an aqueous copper gel electrolyte with cobalt metal organic framework based additive on performance of aqueous-dye-sensitized solar cells

A simple mono-dentate ligand substitution approach was studied to design three new potential tunable heteroleptic copper redox mediators with general formula [Cu (bnbip) (X)](1+/2+) where, bnbip is a tridentate ligand, (2,6-bis(1-(naphthalen-2-ylmethyl)-1H-benzo[d]imidazol-2-yl)pyridine), X = 4-tert-butylpyridine (tbp), 4-chloropyridine (cp) and 5-methoxy-1-(pyridin-4-yl)-1H-indole (mpi). Herein, copper mediator bearing bulky high donor ligand (mpi) reached best redox potential of 0.72 V vs NHE, which directly improves V-oc and J(sc) of the dye sensitized solar cells (DSSC) devices because of its lower reorganization energy and driving force. A series of six aqueous gel electrolytes were prepared as G-1, G-2, G-3 (without additive) and G-4, G-5, G-6 (with Co-MOF additive) to analyze the role of three different heteroleptic copper redox couples and Co-MOF in aqueous gel rite polymer electrolytes. Impressively, electrolytes G-4, G-5 and G-6 affords higher PCE of 2.03, 2.12 and 3.42% under 1sun condition than electrolytes without additives, which proves the role of Co-MOF as an additive to reduce recombination process. This control in recombination occurred due to high interaction of repeating carboxylate donor groups of additive with TiO2 surface and Cu2+ ion of redox pair. The electrolyte material G-6 consists of Cu+1/+2[(bnbip)(mpi)] redox mediator, Co-MOF additive and aqueous geltrite polymer host obtained higher J(sc) and PCE which were sustained via many aspects, such as high conductivity, larger charge, higher chemical capacitance, longer electron lifetime, a shift in the quasi-Fermi level of TiO2, lower recombination of electrons and fast dye regeneration.