Spatially resolved sources of dark current from TiO2 nanoparticle electrodes

Area of Science:

• Materials Science
• Electrochemistry
• Renewable Energy

Background:

• Dye-sensitized solar cells (DSSCs) require efficient charge transport and minimal recombination.
• Blocking layers are crucial for preventing undesirable back electron transfer at the conductive substrate.
• Titanium dioxide (TiO2) and polyphenyl oxide (PPO) are potential materials for blocking layers in DSSCs.

Purpose of the Study:

• To compare the properties of TiO2 and PPO blocking layers in DSSCs.
• To elucidate the mechanisms behind dark current features in DSSCs with different blocking layers.
• To evaluate the impact of blocking layers on electron transfer dynamics.

Main Methods:

• Fabrication of DSSCs with TiO2 and PPO blocking layers.
• Analysis of dark current versus applied potential curves.
• Cyclic voltammetry and electrochemical impedance spectroscopy (EIS) for mechanistic investigation.

Main Results:

• The dark current in DSSCs with TiO2 blocking layers exhibited two distinct features related to electron transfer.
• The first feature originated from electron transfer at the TiO2 blocking layer and the adjacent TiO2 nanoparticle film.
• The second feature was attributed to decreased transport resistance within the nanoparticle film, enabling broader electron transfer.
• PPO blocking layers effectively suppressed back electron transfer from the conductive substrate across all potentials.
• The TiO2 blocking layer actively participated in electron transfer, comparable to the TiO2 nanoparticle film.

Conclusions:

• PPO serves as an effective barrier against back electron transfer in DSSCs.
• TiO2 blocking layers, while preventing some recombination, actively contribute to electron transfer processes.
• Understanding these distinct behaviors is crucial for optimizing blocking layer selection and DSSC performance.