Narrow Results

It is well known that electron transport layer (ETL) plays an indispensable role in the planar heterojunction perovskite solar cells (PSCs). TiO₂ is widely used as an ETL material due to its excellent transport properties, however, the presence of defects in the TiO₂ layer diminishes the power conversion efficiency (PCE) of the devices. Herein, we introduce a method of low-temperature TiCl₄ treatment to deposit a TiO_x layer on the surface of TiO₂ film, which can effectively passivate trap states at the TiO₂ surface. Moreover, the treating process is optimized to be 30min using a 40mM TiCl₄ aqueous solution. Benefiting from this, we obtain the champion device with the highest PCE of 18.47%, which is mainly due to the reduction of surface defects and the deposition of the well-crystallized perovskite films. Besides, the modified PSCs exhibit an average PCE of 17.59%, which is much better than the control devices.

Decreasing the scale of vanadium dioxide (VO₂) structures is one of the ways to enhance the switching speed of the material. We study the properties of VO₂ films of altered thicknesses in the range of 20–170nm prepared on c-sapphire substrates with a TiO₂ sublayer by pulsed laser deposition (PLD) method. The synthesis regime to design a TiO₂ film was preliminarily optimized based on XRD data. XRD patterns reveal an epitaxial growth of the VO₂ films with distortion of the monoclinic cell to hexagonal symmetry. The positions of the lattice vibration modes in Raman spectra are similar to those in bulk VO₂ when the film thickness is greater than $\sim 30$nm. For VO₂ films thicker that $\sim 20$nm, a lattice strain results in the modes’ positions and intensity change. However, the electrically triggered transition in a $\sim 50$nm thick VO₂ film reveals forward and reverse switching times as short as 20ns and 400ns, correspondingly.

N-doped titanium dioxide (TiO${}_2)$ hollow nanospheres with abundant oxygen vacancies were successfully synthesized by coupling urea treatment and annealing in an N₂ atmosphere. The pristine TiO₂ hollow nanospheres exhibit a shallow donor level for electron trapping, while the urea treatment generates a N 2p acceptor level for hole trapping. After annealing in N₂, the sufficient N atoms generate abundant oxygen vacancies for trapping electrons, resulting in further improved charge separation efficiency. The N-doped TiO₂ exhibits the highest H₂ evolution rate, reaching 2867$\mu$molg${}^{-1}$h${}^{-1}$, which is six times higher than that of pristine TiO₂ hollow nanospheres. The introduction of oxygen vacancies by interstitial N provides a promising way to improve the photocatalysis activity of photocatalysts.