Most antisolvents employed in previous research were miscible with perovskite precursor solution. They always led to fast formation of perovskite even if the intermediate stage existed, which was not beneficial to obtain high quality perovskite films and made the formation process less controllable. In this work, a novel ethyl ether/n-hexane mixed antisolvent (MAS) was used to achieve high nucleation density and slow down the formation process of perovskite, producing films with improved orientation of grains and ultrasmooth surfaces. These high quality films exhibited efficient charge transport at the interface of perovskite/hole transport material and perovskite solar cells based on these films showed greatly improved performance with the best power conversion efficiency of 17.08%. This work also proposed a selection principle of MAS and showed that solvent engineering by designing the mixed antisolvent system can lead to the fabrication of high-performance perovskite solar cells.

Pore size and porosity of the porous materials play an important role in catalysis, dye-sensitized solar cells and mesoscopic perovskite solar cells (PSC), etc. Increasing pore size and porosity of mesoporous TiO 2 is crucial for facilitating porefilling of perovskite, charge extraction on TiO 2 /CH 3 NH 3 PbI 3 interface and thus cell performance enhancement. Highly porous TiO 2 films (TFs) with a large pore size that extends the limit of particle size have been achieved through a novel TiO 2 paste using copolymer P123 as a pore-adjusting agent and 2-butoxyethyl acetate as a solvent. A highly porous structure with the pore size of 34.2 nm and porosity of 73.5% has been obtained, the porosity of which is the largest that has ever been reported in the screenprinted TiO 2 thick films. The pore size and porosity of TFs can be successively adjusted in a certain range by tuning the P123 content in the pastes. As particle size and surface area of TFs are kept almost constant, the specific investigation on the effect of varied pore size on the performance of bilayer-structured PSCs becomes possible. The hysteresis phenomenon, the notorious problem of PSCs, is found to depend greatly on pore size and porosity of TFs, that is, pore-filling of perovskite. The suppressing effect of highly porous TFs on hysteresis by avoiding charges accumulation on the interface due to enhanced interfacial contact is proved by the invariable photocurrent response after prebias treatment. A hysteresis-free solar cell with an efficiency of 15.47% was achieved by depositing a 242 nm-thick perovskite capping layer upon 350 nm-thick TF with a pore size of 34.2 nm. This method developed for the preparation of highly porous TFs provides a new way to fabricate hysteresis-free PSCs and is widely applicable for the fabrication of other mesoporous metal oxide films with large pore sizes.

The properties of perovskite films are sensitive to the fabrication method, which plays a crucial role in the performance of perovskite solar cell. In this work, we fabricate organo-lead iodide perovskite on mesoporous TiO2 films through two different two-step deposition methods, respectively, for the purpose of studying the crystal growth of perovskite film and its effect on light harvesting efficiency, defect density, charge extraction rate, and energy levels. The crystal growth exerts a significant influence on the morphology and hence the film properties, which are found to correlate with the performance of solar cells. It is found that vapor deposition of methylammonium iodide in the PbI2 lattice gives a more complete coverage on mesoporous TiO2 with a flatter surface and Fermi level closer to the middle of the band-gap, resulting in higher light absorption in the visible spectral region, lower defect density, and faster charge extraction, as compared to the sequential solution deposition. For this reason, the vapor-processed perovskite film achieves higher short-circuit photocurrent and power conversion efficiency than the solution-processed film.