Characterization of the Pore Filling of Solid State Dye Sensitized Solar Cells with Photoinduced Absorption Spectroscopy

Abstract

Near steady-state photoinduced absorption (PIA) and UV-Vis absorption spectroscopy are used to characterize the pore filling of spiro-MeOTAD (2,2′,7,7′-tetrakis-(N,N-di-p-methoxyphenylamine)9,9′-spirobifluorene) into the nanoparticulate TiO2electrode of a solid-state dye-sensitized solar cell (ssDSC). The volumetric ratio of filled to unfilled pore volumes, as well as the optical signature of interacting chemical species, that is, the hole-transfer yield (HTY), are investigated. PIA spectroscopy is used to measure the HTY, relative to the amount of spiro-MeOTAD present, without needing to determine the extinction coefficients of the dye and spiro-MeOTAD cation species. The Beer-Lambert law is used to relate the relative PIA signal to the penetration length of the hole-conductor in the TiO2film. For the sample thickness range of1.4–5 μm investigated here, the optimum characteristic penetration length is determined to be3.1+0.46 μm, which is compared to 1.4 μm for the 200 mgmL−1concentration of spiro-MeOTAD conventionally used. Therefore, doubling the effective penetration of spiro-MeOTAD is necessary to functionalize all the dye molecules in a ssDSC.

Unravelling the mechanism of photoinduced charge transfer processes in lead iodide perovskite solar cells

“…The corresponding fast component developed within 40-60 ps for all samples, while a slower component appeared in the 140-270 ps time range. The 1.4 mm probe wavelength was initially selected to probe oxidized spiro-OMeTAD, which absorbs in the near-infrared 15,16 . However, samples deprived of HTM yielded an important transient absorption signal originating from the perovskite itself.…”

“…Here, in contrast to the case of perovskite deposited on Al 2 O 3 and in contact with the HTM, no residual absorption is observable on the nanosecond timescale, as every carrier in the perovskite should have found an opposite charge with which to recombine. It could be argued that the longlived absorption actually results from the contribution of oxidized spiro-OMeTAD molecules-h þ (HTM)-as well as that of conduction-band electrons in TiO 2 , as both species absorb at 1.4 mm (refs [15][16][17]. However, this would not affect the reasoning above, as it would also provide direct evidence of charges having been separated at the junctions.…”

Two Channels of Charge Generation in Perylene Monoimide Solid‐State Dye‐Sensitized Solar Cells

“…[20][21][22] As the PIA of the dye cations was found to be entirely absent in the presence of spiro-MeOTAD, it appears that the pore fi lling was suffi cient to regenerate virtually all oxidized dye molecules. This is because the dye cation is reduced by hole transfer to the hole transport material in sample 3, so the long-lived states are the oxidized hole transport material and an electron in titania rather than the dye cation and electron in titania present in sample 2.…”

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

“…The pore filling has long been considered an important factor in the performance of ss-DSCs and was suggested to influence the charge transport and recombination kinetics in the solar cells [8]. Several works have studied the pore-filling effect on cell performance by varying the HTM molecular weight, concentration, or TiO 2 film thickness [8,11,13,[18][19][20]. Schmidt-Mende et al [21] used cross-sectional scanning electron microscopy (SEM) to determine the pore filling of three different HTMs.…”