TiO₂ is widely used in photovoltaic field like dye-sensitized solar cells, quantum dot-sensitized solar cells and so on because of its proper forbidden band width, good optical and chemical stability, nontoxicity, corrosion resistance and simple manufacturing process etc. Recently, inorganic-organic hybrid perovskite solar cell has attracted great attention as a new class of photovoltaic devices and its rapid development has led the power conversion efficiency up to 20%. TiO₂ nanomaterial appears to be a good candidate to be applied in it, which is usually used as compact layer or skeleton layer in perovskite solar cells. As an important part, its crystalline phase, particle size, morphology, preparation methods, film thickness and coverage have great influence on the performance of solar cells. This paper summarizes recent progress of titanium dioxide in the application of perovskite solar cells. We introduce the role TiO₂ play in constructing perovskite solar cells and discuss different preparation methods (high/low temperature) and various optimization methods (modulation of structure, size, shape and interface interaction) of TiO₂. What's more, we analyze the influence of these differences on the performance of perovskite solar cells. In the end, further optimization of TiO₂ materials in the applications of perovskite solar cells is also prospected.

Contents
1 Introduction
2 Recent progress of TiO₂ compact layer
2.1 Preparation methods of TiO₂ compact layer
2.2 Interface optimization of TiO₂ compact layer
2.3 The film thickness of TiO₂ compact layer
3 Recent progress of TiO₂ scaffold layer
3.1 Particle size, pore size and film thickness of TiO₂ scaffold layer
3.2 Crystal phase and morphology of TiO₂
3.3 Surface treatment of TiO₂ scaffold layer
3.4 The influence of TiO₂ on J-V hysteresis
4 Conclusion and prospects