Blacking FTO by strongly cathodic polarization with enhanced photocurrent

- Transparent FTO became blackish under strongly cathodic polarization.
- Part of SnO2 coating on the FTO can be reduced into Sn nanoparticles.
- The black FTO increased solar absorption and enhanced photocurrent responses.
- Take care in photoelectrochemistry test while FTO is strongly cathodically polarized.