Disclosing the hidden presence of Ti3+ ions in different TiO2 crystal structures synthesized at low temperature and photocatalytic evaluation by methylene blue photobleaching

Acetylacetone modulated TiO 2 nanoparticles for low‐temperature solution processable perovskite solar cell

“…While dominant oxidation states of Ti in TiO 2 are, Ti 4+ species, Ti 3+ oxidation state with hydroxyl termination is also observed in both samples at 458.0 and 463.3 eV. Previous studies have reported that anatase phase TiO 2 possesses a lower vacancy formation energy and accompanies the inevitable formation of Ti 3+ surface defect states, especially during low‐temperature solution synthesis 52,53 . Such Ti 3+ species originate from dangling bonds and are undesirable in TiO 2 ETL because they induce photocatalytic activity and create mid‐gap states that act as trap centers 54,55 .…”

“…Previous studies have reported that anatase phase TiO 2 possesses a lower vacancy formation energy and accompanies the inevitable formation of Ti 3+ surface defect states, especially during low-temperature solution synthesis. 52,53 Such Ti 3+ species originate from dangling bonds and are undesirable in TiO 2 ETL because they induce photocatalytic activity and create mid-gap states that act as trap centers. 54,55 The O 1 s spectra in Figure 3B depict a tailing peak with a major peak at 529.8 eV corresponding to Ti-O-Ti from the lattice structure, and another at 531.1 eV, corresponding to Ti-OH bonds from surface states for both samples.…”

Overcoming the Interfacial Photocatalytic Degradation of Nonfullerene Acceptor-Based Organic Photovoltaics by Introducing a UV-A-Insensitive Titanium Suboxide Layer

“…39−41 Accordingly, the intensity of lattice oxygen (O L ) increases and the intensity of −OH bond and oxygen vacancy (O V ) decreases with the addition of water in O 1s spectra. 39,40,42 By using TiO X as the ETL, we obtained highperformance NFA-based OPVs, even showing no light-soaking problem (see the detailed information in the device performance part in the experimental section and in the Supporting Information). As shown in Figure 1b, we confirmed that the newly fabricated TiO X film (E g ∼3.68 eV) has a higher optical bandgap than that of the glass/ITO substrate (3.67 eV).…”

“…To suppress this photodecomposition, we developed a UV-A-insensitive TiO X ETL for NFA-based OPVs by a novel blending method. Although the wide bandgap TiO X ETL was already reported for OPVs in previous works, the synthetic route for its precursor solution, which followed the conventional synthetic process that uses a three-necked flask for reflux in Ar-filled conditions, has problems such as being time-consuming and having poor reproducibility. ,, Moreover, the fabricated TiO X ETL showed a notorious light-soaking problem that resulted in a decreased PCE of OPVs, thereby limiting its usage to only fullerene-based OPVs. − Herein, by adding a small amount of water during the blending process for preparing the TiO X precursor solution, we induced a prehydrolysis step to increase the Ti–O–Ti connectivity, which led to a dense gel network in a film form. − As shown in Figure S4, X-ray photoelectron spectroscopy (XPS) spectra show that the intensity of Ti 3+ ions, which is correlated to the defect in the TiO X film, decreased with the addition of water in Ti 2p spectra. − Accordingly, the intensity of lattice oxygen (O L ) increases and the intensity of −OH bond and oxygen vacancy (O V ) decreases with the addition of water in O 1s spectra. ,, By using TiO X as the ETL, we obtained high-performance NFA-based OPVs, even showing no light-soaking problem (see the detailed information in the device performance part in the experimental section and in the Supporting Information). As shown in Figure b, we confirmed that the newly fabricated TiO X film (E g ∼3.68 eV) has a higher optical bandgap than that of the glass/ITO substrate (3.67 eV).…”