The Effect of Hole Transport Material Pore Filling on Photovoltaic Performance in SolidState DyeSensitized Solar Cells

A detailed investigation of the effect of hole transport material (HTM) pore fi lling on the photovoltaic performance of solid-state dye-sensitized solar cells (ss-DSCs) and the specifi c mechanisms involved is reported. It is demonstrated that the effi ciency and photovoltaic characteristics of ss-DSCs improve with the pore fi lling fraction (PFF) of the HTM, 2,2’,7,7’-tetrakis-( N , N -dip -methoxyphenylamine)9,9’-spirobifl uorene(spiro-OMeTAD). The mechanisms through which the improvement of photovoltaic characteristics takes place were studied with transient absorption spectroscopy and transient photovoltage/photocurrent measurements. It is shown that as the spiroOMeTAD PFF is increased from 26% to 65%, there is a higher hole injection effi ciency from dye cations to spiro-OMeTAD because more dye molecules are covered with spiro-OMeTAD, an order-of-magnitude slower recombination rate because holes can diffuse further away from the dye/HTM interface, and a 50% higher ambipolar diffusion coeffi cient due to an improved percolation network. Device simulations predict that if 100% PFF could be achieved for thicker devices, the effi ciency of ss-DSCs using a conventional rutheniumdye would increase by 25% beyond its current value.