Effect of Posttreatment of Titania Mesoscopic Films by TiCl₄ in Solid-State Dye-Sensitized Solar Cells: A Time-Resolved Spectroscopy Study

Abstract

Posttreatment of mesoporous titanium dioxide films by TiCl 4 solutions is commonly applied during the fabrication of solid-state dye-sensitized solar cells (ssDSCs), as this operation markedly improves the performance of the photovoltaic device. The effect of the posttreatment upon the charge carrier dynamics was scrutinized in an ssDSC aiming at unraveling its mechanism. Kinetic studies carried out using femtosecond and nanosecond transient absorption spectroscopies showed that a biphasic electron injection from the dye excited state is observed, for both treated and nontreated films, whose kinetics is not significantly affected by the surface modification step. However, hole injection in the hole transport material (HTM) spiro-OMeTAD and charge recombination were found to be markedly slower in TiCl 4 -treated films. These findings are rationalized by a model describing the interaction at the interface between TiO 2 , the dye-sensitizer, and spiro-OMeTAD. Rather than resulting from a modification of the energetics of the conduction band of the oxide, the effect of the TiCl 4 posttreatment appears to be associated with a subtle change of the film morphology. Results emphasize the importance of controlling the contact at the heterojunction between the HTM and the sensitized semiconductor oxide network.

Ultrafast charge separation dynamics in opaque, operational dye-sensitized solar cells revealed by femtosecond diffuse reflectance spectroscopy

“…The small particles based films are the only morphology that has been studied to date. In earlier studies of small TiO 2 particles sensitized with Ru dyes based on transient absorption spectroscopy at visible or NIR region or by 2D-IR spectroscopy 23 31 32 33 , such electron back recombination was not observed and the oxidized dye molecule was accepted to be stable until much longer time scale of microseconds. We observe that the kinetics is accelerated in full device relative to what is so far accepted for small particles.…”

“…We applied this technique to the study of Z907 dye-sensitized TiO 2 films, which are from the same family of N719 and N3 Ru-based dyes. According to earlier transient absorption studies on N719 (cis-bis (isothiocyanate)bis(4,4′-dicarboxylic-2,2′-bipyridyl) ruthenium(II)) and N3 (cis-di(thiocyanate)bis(2,2′-bipyridyl-4,4′-dicarboxylic acid)ruthenium(II)) dye-sensitized TiO 2 films, the transient absorption spectrum around 800 nm is assigned to the oxidized dye molecules 13 23 24 25 and the absorption spectrum around 1200 nm is attributed to absorption by conduction band electrons 13 26 27 . The kinetics of electron injection in the complete device is studied by monitoring the evolution of oxidized dye molecules and photo-injected electrons in TiO 2 .…”

Tuning of perovskite solar cell performance via low-temperature brookite scaffolds surface modifications

“…1) image that the treatment of brookite mesoporous layer at relatively low temperatures decreased the surface roughness of the substrates and reduced the trap density of TiO 2 . 44,45 Further, the loading of perovskite depends on the nature of scaffolds layer, and in the present case 40 ST samples have shown the best coverage of perovskite (Fig. S2 b of the supplementary material).…”

“…On the other hand, TiCl 4 is commonly used in dye sensitized solar cells (DSSCs) to modify the surface of the mesoporous TiO 2 layer via enhancing bonding between nanoparticles and retarding charge recombination. 44,45 The reported works used TiCl 4 treatments of anatase mesoporous films which further need high temperature annealing (500 • C) of treated samples. The high temperature annealing is not suitable for flexible substrates.…”

Optimization of Experimental Parameters for the Performance of Solid-state Dye-sensitized Solar Cells

“…For example, the optimization of the thickness of a TiO2 layer is necessary to compromise the maximization of the amount of adsorbed dyes and the collection of the electrons transported inside 1 ; only a limited number of dyes and hole transfer materials (HTMs) were implemented for the actual device, 2 various additives or surface treatments were necessary, [3][4][5] and a TiO2 blocking layer is always necessary, different from the DSCs with liquid electrolytes, 6 etc. To study the effects of dyes, HTMs and surface treatments, time-resolved dynamics studies have been utilized and such effects have been clarified from the direct information of excited carriers such as their injection and recombination processes.…”