Random nanowires of nickel doped TiO₂ with high surface area and electron mobility for high efficiency dye-sensitized solar cells

Mesoporous TiO2 with a large specific surface area (∼150 m² g⁻¹) is the most successful material in dye-sensitized solar cells so far; however, its inferior charge mobility is a major efficiency limiter. This paper demonstrates that random nanowires of Ni-doped TiO₂ (Ni:TiO₂) have a dramatic influence on the particulate and charge transport properties. Nanowires (dia ∼60 nm) of Ni:TiO₂ with a specific surface area of ∼80 m2 g⁻¹ were developed by an electrospinning technique. The band gap of the Ni:TiO₂ shifted to the visible region upon doping of 5 at% Ni atoms. The Mott–Schottky analysis shows that the flat band potential of Ni:TiO₂ shifts to a more negative value than the undoped samples. The electrochemical impedance spectroscopic measurements showed that the Ni:TiO₂ offer lower charge transport resistance, higher charge recombination resistance, and enhanced electron lifetime compared to the undoped samples. The dye-sensitized solar cells fabricated using the Ni:TiO₂ nanowires showed an enhanced photoconversion efficiency and short-circuit current density compared to the undoped analogue. The transient photocurrent measurements showed that the Ni:TiO₂ has improved charge mobility compared with TiO₂ and is several orders of magnitude higher compared to the P25 particles.