Enhanced performance of perovskite solar cells based on vertical TiO ₂ nanotube arrays with full filling of CH ₃ NH ₃ PbI ₃

Due to a wide range of intriguing properties, such as efficient one-dimensional (1D) electron pathways and extraordinarily large surface areas, titanium dioxide (TiO ₂ ) nanotube arrays are considered as the promising electron transport material for high-performance perovskite solar cells (PVSCs). However, it is still a great challenge to directly synthesize the TiO ₂ nanotube arrays with well-controlled geometries (e.g., diameter and height, etc.) on the surface of fluorine-doped tin oxide (FTO). Here, vertically standing TiO ₂ nanotube arrays with desirable heights and diameters are directly synthesized on the FTO surface by employing the aqueous TiO ₂ sol-gel method on tubular photoresist templates. The tube height can be precisely tailored within a range of 350–900 nm for the effective loading of perovskite precursor solution. Importantly, it is demonstrated that TiO ₂ nanotube arrays with the optimized tube diameter and length can facilitate the infiltration of perovskite precursor solution, and thus ensuring the formation of a dense, smooth and large grain-sized perovskite film. Moreover, the contact between the perovskite and TiO ₂ nanotube arrays are enhanced simultaneously. Benefiting from the high-quality perovskite film, good interfacial contact at the perovskite/TiO ₂ tube interface, enhanced light trapping as well as rapid electron collection and transport induced by one-dimensional TiO ₂ nanotubes, the fabricated PVSCs exhibit an impressive power conversion efficiency (PCE) of up to 14.13%. Our work does not only demonstrate the promising potential of vertical TiO ₂ nanotube arrays for PVSCs, but also provides valuable insights into the design and utilization of TiO ₂ nanotubes for practical applications.