Photospectroscopy of I3-species in dye solar cells (DSC) as a test for the sealing and diffusion barrier properties of glass frit
To ensure long-term stable dye-sensitized solar cells (DSCs) and modules a hermetic sealing is required. This research investigates the chemical stability of I-/I3- redox electrolyte and four different glass frits (GF). Sintered GF layers were openly exposed to non-aqueous redox electrolyte and redox electrolyte with 1, 5 and 10 wt% H2O in thin, encapsulated cells. The I3- absorbance change was monitored over 100 days. The change in I3- absorbance was assigned to a reaction between the GF and I-/I3- electrolyte and was used to evaluate the chemical stability of the different GFs. Two out of the four investigated GFs were unstable when H2O was added to the redox electrolyte. The effect of H2O caused metal ion leaching which was determined from EDX analysis of evaporated electrolyte samples. A GF based on Bi2O3-SiO2-B2O3 with low bond strength leached bismuth into electrolyte, and formed the BiI4- complex. A GF based on ZnO-SiO2-Al2O3 also became unstable when H2O was added to redox electrolyte. Leaching of zinc ions due to exchange with H+ resulted in the formation of a zinciodine complex which caused I3- depletion. By applying the test design to different types of GFs, the material suitability in the DSC working environment was investigated.