Electrolyte Effects on Electron Transport and Recombination at ZnO Nanorods for Dye-Sensitized Solar Cells

Abstract

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 (τn), improved electron transport, and reduced collection time (τd) on nd-ZnO. In addition, they improved the electron diffusion coefficient (Dn) and elongated the effective diffusion length (Ln). 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·cm2 at the electrolyte/Pt interface. Nd-ZnO DSSCs using different electrolytes were tested and the improvement of open circuit voltage (Voc), short circuit current density (Jsc), fill factor (FF), and incident photon to electron conversion efficiency (IPCE) was in good agreement with the findings from the EIS data.