Electrolyte effects on electron transport and recombination at ZnO nanorods for dye-sensitized solar cells

Electrolyte effects on electron transport and recombination at ZnO nanorods (nd-ZnO) were studied by electrochemical impedance spectroscopy (EIS) in dye-sensitized solar cells (DSSCs). Different electrolyte systems were prepared by gradually adding tert-butylpyridine (TBP) and guanidinium thiocyanate (GuSCN) and replacing LiI with 1-butyl-3-methylimidazolium iodide (BMII). The introduction of TBP and GuSCN, and the replacement of LiI with BMII suppressed charge recombination at the nd-ZnO/electrolyte interface, increased electron lifetime (τ_n), improved electron transport, and reduced collection time (τ_d) on nd-ZnO. In addition, they improved the electron diffusion coefficient (D_n) and elongated the effective diffusion length (L_n). The electron transfer coefficient (β) at the ZnO/electrolyte interface was increased from 0.34 to 0.44, which was a good sign of improvement in fill factor (FF). In addition, the ohmic series resistance was reduced from 17.35 to 4.99 Ω•cm² and the charge transfer resistance was decreased from 18.49 to 7.09 Ω•cm ² at the electrolyte/Pt interface. Nd-ZnO DSSCs using different electrolytes were tested and the improvement of open circuit voltage (V _oc), short circuit current density (J_sc), fill factor (FF), and incident photon to electron conversion efficiency (IPCE) was in good agreement with the findings from the EIS data.