200-nm long TiO2 nanorod arrays for efficient solid-state PbS quantum dot-sensitized solar cells

Abstract

To ensure the infiltration of spiro-OMeTAD into the quantum dot-sensitized photoanode and to consider the limit of the hole diffusion length in the spiro-OMeTAD layer, a rutile TiO2 nanorod array with a length of 200 nm, a diameter of 20 nm and an areal density of 720 µm−2 was successfully prepared using a hydrothermal method with an aqueous-grown solution of 38 mM titanium isopropoxide and 6 M hydrochloric acid at 170 °C for 75 min. PbS quantum dots were deposited by a spin coating-assisted successive ionic layer adsorption and reaction (spin-SILAR), and all solid-state PbS quantum dot-sensitized TiO2 nanorod array solar cells were fabricated using spiro-OMeTAD as electrolytes. The results revealed that the average crystal size of PbS quantum dots was ∼7.8 nm using Pb(NO3)2 as the lead source and remain unchanged with the increase of the number of spin-SILAR cycles. The all solid-state PbS quantum dot-sensitized TiO2 nanorod array solar cells with spin-SILAR cycle numbers of 20, 30 and 40 achieved the photoelectric conversion efficiencies of 3.74%, 4.12% and 3.11%, respectively, under AM 1.5 G illumination (100 mW/cm2).