Pore Filling of Spiro‐OMeTAD in Solid‐State Dye‐Sensitized Solar Cells Determined Via Optical Reflectometry

Abstract

Here, we present an optical probe to determine the pore-filling fraction of the hole-conductor 2,2-7,7-tetrakis-N,N-di-pmethoxyphenylamine-9,9-spirobifluorene (spiro-OMeTAD) into mesoporous photoanodes in solid-state dye-sensitized solar cells (ss-DSCs). Based on refractive index determination by the film's reflectance spectra, and using effective medium approximations, we can extract the volume fractions of the constituent materials and hence quantify pore-filling. This non-destructive method can be used with complete films and does not require detailed model assumptions.pore-filling fractions of up to 80% were estimated for optimized solid-state DSC photoanodes, which is higher than that previously estimated by indirect methods.Additionally, we have determined transport and recombination lifetimes as a function of the pore-filling fraction via photovoltage and photocurrent decay measurements. While extended electron lifetimes were observed with increasing pore-filling fractions, no trend was found in the transport kinetics. The data suggests that a pore-filling fraction of at least 60% is necessary to achieve optimized performance in ss-DSCs. This degree of pore-filling is even achieved in 5 µm thick mesoporous photoanodes. We can therefore conclude from this study that pore-filling is not a limiting factor in the fabrication of thick ss-DSCs.

Enhancing the Optoelectronic Performance of Perovskite Solar Cells via a Textured CH3NH3PbI3 Morphology

“…The refractive indices of CH 3 NH 3 PbI 3 and spiro-OMeTAD, for a 600 nm light source, have been previously reported as ≈2.7 and 1.93, respectively. [ 37 ] The signifi cant difference between these refractive indices allows for determinate optical effects at the material interfaces. We noted from the SEM and TEM cross-sections that the perovskite and spiro-OMeTAD layers formed a continuous interface throughout the textured perovskite structure.…”

Enhanced pore filling of spiro-OMeTAD by enlarging the porosity of TiO2 films and its effects on the photovoltaic performance of ss-DSCs

“…Another simple method of optical reflectometry was also utilized as reported by Docampo et al [22] to calculate the porosity of the films (details see the supporting information). Results showed the same trend, and the porosity of films was 49 ± 2, 51 ± 2, 54 ± 2, and 59 ± 2 % for R1, R2, R3, and R4, respectively.…”

“…However, thick films inhibit the penetration of spiro-OMeTAD, thus resulting in poor cell efficiency. Docampo et al [22] measured the pore-filling fractions of spiro-OMeTAD at a series of concentrations in TiO 2 films about 2.8 lm thick by using optical absorbance measurements. They further studied the electron transport and recombination lifetime in corresponding ss-DSCs.…”

Efficiency enhancement in solid state dye sensitized solar cells by including inverse opals with controlled layer thicknesses

“…Thus, durability issues for standard DSCs arise from the use of organic liquid electrolytes containing the iodide/tri-iodide redox couple that can give rise to electrode corrosion or electrolyte leakage. To circumvent this drawback, all solid-state dye-sensitized solar cells (ssDSCs) have been designed by hole transport materials (HTM) [16][17][18][19] as Spiro-OMeTAD or p-type inorganic semiconductor [20]. For instance, optimization of the dye structure employed and suitable doping of SpiroOMeTAD led to energy conversion efficiencies over 7% [21,22].…”