Characterization of Perovskite Obtained from Two-Step Deposition on Mesoporous Titania

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

Pore Size Dependent Hysteresis Elimination in Perovskite Solar Cells Based on Highly Porous TiO₂ Films with Widely Tunable Pores of 15–34 nm

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 TiO₂ is crucial for facilitating pore-filling of perovskite, charge extraction on TiO₂/CH₃NH₃PbI₃ interface and thus cell performance enhancement. Highly porous TiO₂ films (TFs) with a large pore size that extends the limit of particle size have been achieved through a novel TiO₂ 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 screen-printed TiO₂ 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

Fast and Controllable Crystallization of Perovskite Films by Microwave Irradiation Process

The crystal growth process significantly influences the properties of organic–inorganic halide perovskite films along with the performance of solar cell devices. In this paper, we adopted the microwave irradiation to treat perovskite films through a one-step deposition method for several minutes at a fixed output power. It is found that the specific microwave irradiation process can evaporate the solvent directly and heat perovskite film quickly. In comparison with the conventional thermal annealing process, a microwave irradiation process assisted fast and controllable crystallization of perovskite films with less energy-loss and time-consumption and therefore resulted in the enhancement in the photovoltaic performance of the corresponding solar cells

Ultrasmooth Perovskite Film via Mixed Anti-Solvent Strategy with Improved Efficiency

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/<i>n</i>-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

Achieving High Current Density of Perovskite Solar Cells by Modulating the Dominated Facets of Room-Temperature DC Magnetron Sputtered TiO₂ Electron Extraction Layer

The short circuit current density of perovskite solar cell (PSC) was boosted by modulating the dominated plane facets of TiO₂ electron transport layer (ETL). Under optimized condition, TiO₂ with dominant {001} facets showed (i) low incident light loss, (ii) highly smooth surface and excellent wettability for precursor solution, (iii) efficient electron extraction, and (iv) high conductivity in perovskite photovoltaic application. A current density of 24.19 mA cm^–2 was achieved as a value near the maximum limit. The power conversion efficiency was improved to 17.25%, which was the record value of PSCs with DC magnetron sputtered carrier transport layer. What is more, the room-temperature process had a great significance for the cost reduction and flexible application of PSCs

Novel Perovskite Solar Cell Architecture Featuring Efficient Light Capture and Ultrafast Carrier Extraction

A new perovskite solar cell (PSC) structure with a functionalized interface between perovskite and a hole transport material has been proposed in this report. The short circuit current density of PSC was notably enhanced with the novel architecture (with an increase of 8.7%), and a power conversion efficiency (PCE) of 16.93% was achieved. With the increased perovskite/hole conductor interface, hysteresis suppression was observed. The advantages of this structure in light-harvesting efficiency, trap density, and carrier separation rate were proved by various characterization and analysis studies. It is noteworthy that a PCE of 14.67% was achieved with poly­(3-hexyl-thiophene), which to our knowledge is the highest performing PSC based on this material