There are three kinds of natural titanium dioxide
which are rutile, anatase, and brookite respectively. The rutile type is the most stable of the three of them. When the temperature is higher than 650℃, the anatase phase begins to change into the rutile phase. While brookite is only a middle phase in the crystallization process of anatase, and it is generally stable in minerals with impurities. The TiO2 anatase is the most widely used in the research of perovskite solar cells.
Titanium dioxide has the properties of semiconductors, and its conductivity increases rapidly with the rise of temperature, and is also very sensitive to oxygen. For example, rutile titanium dioxide is still an electrical insulator at 20℃, but its electrical conductivity increases by 107 times when it is heated to 420°C. A slight reduction of oxygen content has a special effect on its conductivity. According to the chemical composition of titanium dioxide (TiO2), the conductivity is <10-10 s/cm, while the conductivity of TiO1.9995 is as high as 10-1 s/cm. The dielectric constant and the semiconductor properties of rutile titanium dioxide are very important to the electronics industry. The industrial field makes use of the above characteristics to produce electronic components such as ceramic capacitors.
Because of the better electronic transmission performance of anatase titanium dioxide, more and more photovoltaic devices are used as electron transport materials, and a few researchers use rutile TiO2. In addition to the crystalline form of titanium dioxide, the morphology has an important influence on the light absorption, electron transport and electron capture of the battery. TiO2 nanosheets can improve the contact between perovskite and porous layer, and the TiO2 nanotube electrode with fewer grain boundaries can significantly improve the optical absorption and electronic collection efficiency. The researchers prepared porous nanoscale titanium dioxide fiber with different diameters and different lengths by electrostatic spinning. The results show that the fibers with too small diameter are discontinuous and the fibers with too large diameter are arranged so closely that the perovskite adsorption is hindered.