Highly Bendable Flexible Perovskite Solar Cells on a Nanoscale Surface Oxide Layer of Titanium Metal Plates

We report highly bendable and efficient perovskite solar cells (PSCs) that use thermally oxidized layer of Ti metal plate as an electron transport layer (ETL). The power conversion efficiency (PCE) of flexible PSCs reaches 14.9% with a short-circuit current density (<i>J</i>_sc) of 17.9 mA/cm², open-circuit voltage (<i>V</i>_oc) of 1.09, and fill factor (ff) of 0.74. Moreover, the Ti metal-based PSCs exhibit a superior fatigue resistance over indium tin oxide/poly­(ethylene terephthalate) substrate. Flexible PSCs maintain 100% of their initial PCE even after PSCs are bent 1000 times at a bending radius of 4 mm. This excellent performance of flexible PSCs is due to high crystalline quality and low oxygen vacancy concentration of TiO₂ layer. The concentration of oxygen vacancies in the oxidized Ti metal surface controls the electric function of TiO₂ as ETL of PSCs. A decrease in the oxygen vacancy concentration of the TiO₂ layer is critical to improving the electron collection efficiency of the ETL. Our results suggest that Ti metal-based PSCs possess excellent mechanical properties, which can be applied to the renewable energy source for flexible electronics

BiVO₄/WO₃/SnO₂ Double-Heterojunction Photoanode with Enhanced Charge Separation and Visible-Transparency for Bias-Free Solar Water-Splitting with a Perovskite Solar Cell

Coupling dissimilar oxides in heterostructures allows the engineering of interfacial, optical, charge separation/transport and transfer properties of photoanodes for photoelectrochemical (PEC) water splitting. Here, we demonstrate a double-heterojunction concept based on a BiVO₄/WO₃/SnO₂ triple-layer planar heterojunction (TPH) photoanode, which shows simultaneous improvements in the charge transport (∼93% at 1.23 V vs RHE) and transmittance at longer wavelengths (>500 nm). The TPH photoanode was prepared by a facile solution method: a porous SnO₂ film was first deposited on a fluorine-doped tin oxide (FTO)/glass substrate followed by WO₃ deposition, leading to the formation of a double layer of dense WO₃ and a WO₃/SnO₂ mixture at the bottom. Subsequently, a BiVO₄ nanoparticle film was deposited by spin coating. Importantly, the WO₃/(WO₃+SnO₂) composite bottom layer forms a disordered heterojunction, enabling intimate contact, lower interfacial resistance, and efficient charge transport/transfer. In addition, the top BiVO₄/WO₃ heterojunction layer improves light absorption and charge separation. The resultant TPH photoanode shows greatly improved internal quantum efficiency (∼80%) and PEC water oxidation performance (∼3.1 mA/cm² at 1.23 V vs RHE) compared to the previously reported BiVO₄/WO₃ photoanodes. The PEC performance was further improved by a reactive-ion etching treatment and CoO_<i>x</i> electrocatalyst deposition. Finally, we demonstrated a bias-free and stable solar water-splitting by constructing a tandem PEC device with a perovskite solar cell (STH ∼3.5%)

Indium–Tin–Oxide Nanowire Array Based CdSe/CdS/TiO₂ One-Dimensional Heterojunction Photoelectrode for Enhanced Solar Hydrogen Production

For photoelectrochemical (PEC) hydrogen production, low charge transport efficiency of a photoelectrode is one of the key factors that largely limit PEC performance enhancement. Here, we report a tin-doped indium oxide (In₂O₃:Sn, ITO) nanowire array (NWs) based CdSe/CdS/TiO₂ multishelled heterojunction photoelectrode. This multishelled one-dimensional (1D) heterojunction photoelectrode shows superior charge transport efficiency due to the negligible carrier recombination in ITO NWs, leading to a greatly improved photocurrent density (∼16.2 mA/cm² at 1.0 V vs RHE). The ITO NWs with an average thickness of ∼12 μm are first grown on commercial ITO/glass substrate by a vapor–liquid–solid method. Subsequently, the TiO₂ and CdSe/CdS shell layers are deposited by an atomic layer deposition (ALD) and a chemical bath deposition method, respectively. The resultant CdSe/CdS/TiO₂/ITO NWs photoelectrode, compared to a planar structure with the same configuration, shows improved light absorption and much faster charge transport properties. More importantly, even though the CdSe/CdS/TiO₂/ITO NWs photoelectrode has lower CdSe/CdS loading (i.e., due to its lower surface area) than the mesoporous TiO₂ nanoparticle based photoelectrode, it shows 2.4 times higher saturation photocurrent density, which is attributed to the superior charge transport and better light absorption by the 1D ITO NWs

Direct Low-Temperature Growth of Single-Crystalline Anatase TiO₂ Nanorod Arrays on Transparent Conducting Oxide Substrates for Use in PbS Quantum-Dot Solar Cells

We report on the direct growth of anatase TiO₂ nanorod arrays (A-NRs) on transparent conducting oxide (TCO) substrates that can be directly applied to various photovoltaic devices via a seed layer mediated epitaxial growth using a facile low-temperature hydrothermal method. We found that the crystallinity of the seed layer and the addition of an amine functional group play crucial roles in the A-NR growth process. The A-NRs exhibit a pure anatase phase with a high crystallinity and preferred growth orientation in the [001] direction. Importantly, for depleted heterojunction solar cells (TiO₂/PbS), the A-NRs improve both electron transport and injection properties, thereby largely increasing the short-circuit current density and doubling their efficiency compared to TiO₂ nanoparticle-based solar cells

A Simple Method To Control Morphology of Hydroxyapatite Nano- and Microcrystals by Altering Phase Transition Route

Hydroxyapatite (HAp) particles with various morphologies such as sphere, rod, whisker, and platelet have attracted a great deal of scientific and technological interest for their broad utilization as reinforcing agents in bone cement, bone fillers, drug carriers, and adsorbents for chromatography. In this Article, a simple method to control the morphology of HAp particles by adjusting the initial pH of precursors and the amount of gelatin and urea additions is introduced. Initially formed calcium phosphate products such as octacalcium phosphate (OCP), hydroxyapatite (HAp), and amorphous calcium phosphate (ACP) are found to be altered by changing the pH of solutions, which induces variation of HAp morphology as well as phase transformation route to HAp. From the observation of HAp formation behavior, the addition of gelatin is revealed to retard HAp formation as well as to change the aspect ratio of HAp particles, which is ascribed to strong adsorption of gelatin on the surface of calcium phosphate. Also, urea is observed to boost HAp formation rate by enhancing hydrolysis reaction. Through the understanding of the influence of the aforementioned variables, the morphology of pure HAp particles is successfully controlled, and this enables the promotion of the applicability of HAp particles in various fields

Reduced Graphene Oxide/Mesoporous TiO₂ Nanocomposite Based Perovskite Solar Cells

We report on reduced graphene oxide (rGO)/mesoporous (mp)-TiO₂ nanocomposite based mesostructured perovskite solar cells that show an improved electron transport property owing to the reduced interfacial resistance. The amount of rGO added to the TiO₂ nanoparticles electron transport layer was optimized, and their impacts on film resistivity, electron diffusion, recombination time, and photovoltaic performance were investigated. The rGO/mp-TiO₂ nanocomposite film reduces interfacial resistance when compared to the mp-TiO₂ film, and hence, it improves charge collection efficiency. This effect significantly increases the short circuit current density and open circuit voltage. The rGO/mp-TiO₂ nanocomposite film with an optimal rGO content of 0.4 vol % shows 18% higher photon conversion efficiency compared with the TiO₂ nanoparticles based perovskite solar cells