MACl-Induced Intermediate Engineering for High-Performance Mixed-Cation Perovskite Solar Cells.

Recently, mixed-cation perovskites have been extensively used for high-performance solar cells. Nevertheless, the mixed-cation perovskite based on formamidinium methylammonium lead tri-iodide (FAxMA1-xPbI3) fabricated through the existing methods often suffers from phase stability and trap density. Herein, we demonstrate a facile intermediate engineering approach to improve the quality of the mixed-cation perovskite based on FAxMA1-xPbI3. Varying concentrations of methylammonium chloride (MACl) are used to treat the FA-MA-PbI3-solvent intermediate. It is noted that MACl has a strong impact on the crystallization kinetics and charge carrier dynamics as well as the defect density of the obtained perovskite. The mixed-cation perovskite treated with 20 mg mL-1 MACl yields a large grain size, highly uniform morphology, and better crystalline stability. Subsequently, the device with an acquired high-quality mixed-cation perovskite shows a high efficiency of 20.40%, which is obviously higher than that obtained from the traditional nontreated method. Moreover, the device prepared through the developed method could retain over 85% of the initial efficiency after 860 h at room temperature.

Enhancing the Phase Stability of Inorganic α-CsPbI3 by the Bication-Conjugated Organic Molecule for Efficient Perovskite Solar Cells.

Inorganic CsPbI3 perovskite has demonstrated promising potentials for photovoltaic applications, whereas the black perovskite polymorph (α phase) of CsPbI3 was easily prone to converting into yellow phase (δ phase) under ambient moist environment, which restrained its practical application and further studies severely. In this study, p-phenylenediammonium iodide (PPDI) was employed to posttreat CsPbI3 films for controlling the phase conversion, strengthening moisture resistance, and improving device performance. The multiple roles of PPDI were as follows: (1) avoiding spontaneous octahedral tilting by ionic bonds between NH3+ of PPD2+ and I- of [PbI6]4-; (2) enhancing the hydrophobicity induced by exactly exposed oil-wet (hydrophobic) benzene rings; and (3) passivating surface defects and filling I vacancies. As a result, after the treatment, mutable a-CsPbI3 could maintain its α phase for at least 30 d in dry air (<20% RH). The perovskite solar cells with PPDI treatment exhibited reproductive photovoltaic performance with a champion power conversion efficiency (PCE) of 10.4, and 91% of the initial PCE was retained after storage for 504 h in a dark dry box without any encapsulation.

Reducing the Universal "Coffee-Ring Effect" by a Vapor-Assisted Spraying Method for High-Efficiency CH3NH3PbI3 Perovskite Solar Cells.

Organic-inorganic perovskite solar cells (PSCs) are one of the most attractive and efficient burgeoning thin-film photovoltaics. The perovskite films have been fabricated via lots of deposition methods, but these laboratory-based fabrication methods are not well-matched with large-area manufacture. Herein, spray coating as a deposition technique was explored to prepare perovskite films and break the bottleneck that plagued large-scale production. However, it is hard to reduce the notorious "coffee-ring effect" during the process of spraying perovskite films especially in a one-step spraying method. Thus, the vapor-assisted spraying method (VASM), namely, fabricating perovskite films through a vapor-solid in situ reaction between CH3NH3I vapor and sprayed PbI2 films, was creatively applied to the preparation of dense and uniform perovskite films. The surfaces of the sprayed PbI2 films were optimized by adjusting the wettability, viscosity, and contact quality via various methods such as the selection of solvent, solution concentration, and substrate temperature to inhibit the capillary flow and release the pinning contact line. The application of a component solvent could effectively crush the dense structure of the PbI2 film, optimizing the morphology of PbI2 films and reducing the influence of the coffee-ring effect. Integrating the above aspects, the optimized PbI2 films could form uniform perovskite films via an in situ reaction, and a best power conversion efficiency of 17.56% was achieved for planar structure PSCs, which is high among the PSCs fabricated by the spraying method. In addition, the VASM could be applied in the actual conditions for mass production, exhibiting excellent optical and electrical properties and paving the way of the commercialization of PSCs.

Incorporating 4-tert-Butylpyridine in an Antisolvent: A Facile Approach to Obtain Highly Efficient and Stable Perovskite Solar Cells.

The synthesis and growth of CH3NH3PbI3 films with controlled nucleation is a key issue for the high efficiency and stability of solar cells. Here, 4-tert-butylpyridine (tBP) was introduced into a CH3NH3PbI3 antisolvent to obtain high quality perovskite layers. In situ optical microscopy and X-ray diffraction patterns were used to prove that tBP significantly suppressed perovskite nucleation by forming an intermediate phase. In addition, a gradient perovskite structure was obtained by this method, which greatly improved the efficiency and stability of perovskites. An effective power conversion efficiency (PCE) of 17.41% was achieved via the tBP treatment, and the high-efficiency device could maintain over 89% of the initial PCE after 30 days at room temperature.

Forming Intermediate Phase on the Surface of PbI2 Precursor Films by Short-Time DMSO Treatment for High-Efficiency Planar Perovskite Solar Cells via Vapor-Assisted Solution Process.

Morphology regulation is vital to obtain high-performance perovskite films. Vapor-assisted deposition provides a simple approach to prepare perovskite films with controlled vapor-solid reaction. However, dense PbI2 precursor films with large crystal grains make it difficult for organic molecules to diffuse and interact with inner PbI2 frame. Here, a surface modification process is developed to optimize the surface layer morphology of PbI2 precursor films and lower the resistance of the induced period in crystallization. The vapor optimization time is shortened to several seconds, and the intermediate phase forms on the surface layer of PbI2 films. We achieve porous PbI2 surface with smaller grains through dimethyl sulfoxide vapor treatment, which promotes the migration and reaction rate between CH3NH3I vapor and PbI2 layer. The PbI2 precursor films undergo dramatic morphological evolution due to the formed intermediate phase on PbI2 surface layer. Taking advantage of the proposed surface modification process, we achieve high-quality uniform perovskite films with larger crystal grains and without residual PbI2. The repeatable perovskite solar cells (PSCs) with modified films exhibit power conversion efficiency of up to 18.43% for planar structure. Moreover, the devices show less hysteresis because of improved quality and reduced defect states of the films. Our work expands the application of morphology control through forming intermediate phase and demonstrates an effective way to enhance the performance of the PSCs.

Incorporating C60 as Nucleation Sites Optimizing PbI2 Films To Achieve Perovskite Solar Cells Showing Excellent Efficiency and Stability via Vapor-Assisted Deposition Method.

To achieve high-quality perovskite solar cells (PSCs), the morphology and carrier transportation of perovskite films need to be optimized. Herein, C60 is employed as nucleation sites in PbI2 precursor solution to optimize the morphology of perovskite films via vapor-assisted deposition process. Accompanying the homogeneous nucleation of PbI2, the incorporation of C60 as heterogeneous nucleation sites can lower the nucleation free energy of PbI2, which facilitates the diffusion and reaction between PbI2 and organic source. Meanwhile, C60 could enhance carrier transportation and reduce charge recombination in the perovskite layer due to its high electron mobility and conductivity. In addition, the grain sizes of perovskite get larger with C60 optimizing, which can reduce the grain boundaries and voids in perovskite and prevent the corrosion because of moisture. As a result, we obtain PSCs with a power conversion efficiency (PCE) of 18.33% and excellent stability. The PCEs of unsealed devices drop less than 10% in a dehumidification cabinet after 100 days and remain at 75% of the initial PCE during exposure to ambient air (humidity > 60% RH, temperature > 30 °C) for 30 days.