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2D Ruddlesden–Popper (RP) layered metal‐halide perovskites have garnered significant interest due to their unique photoelectric properties and excellent stability. However, 2D perovskite films prepared via solution process generally exhibit multi‐quantum well structure with random well width distribution, which significantly impedes the carrier transportation. Herein, the synthesis of phase‐pure 2D (PEA)2FAPb2I7 (PEA = C8H11N, FA = CH4N2) perovskite thin films is reported in ambient environment achieved by suppressing the formation of the 3D perovskite phase. First, incorporation of MACl additive can effectively regulate the intermediate during crystallization, facilitating the formation of a metastable 3D MAxFA1‐xPbIyCl3‐y phase. Second, precise control of environmental humidity is employed to further inhibit the formation of α‐FAPbI3 phase. As a result, the perovskite intermediate composed of predominantly metastable 3D phase and 2D n = 2 phase is achieved, which is eventually transformed into 2D n = 2 perovskite during annealing, leading to markedly enhanced phase purity. Photoconductive‐type photodetectors based on the phase‐pure 2D RP perovskite films are fabricated, demonstrating a high detectivity of over 9.4 × 1012 Jones due to the improved carrier transportation. This study provides a comprehensive insight into the crystallization process of phase‐pure 2D perovskites. [ABSTRACT FROM AUTHOR]

Phase transition during annealing in the two‐step sequential deposition has drawn intensive attention as its significance in fabricating superior perovskite films. However, previous works have not paid enough attention to the importance of the purified phase transition path in the crystallization process. Herein, different from the mixed paths in the conventional cognition, purified phase transition path for α‐FAPbI3 crystallization is achieved by introducing dimethylurea (DMU) into lead iodide (PbI2) precursor solution. The multifunctional molecule is found to design a penetrable porous PbI2 film and fundamentally regulate the perovskite crystallization by forming single phase transition path via the complete δ‐phase during annealing of perovskite. The role of DMU in purified transition path for α‐FAPbI3 crystallization is unraveled with in situ photoluminescence and grazing incidence wide‐angle x‐ray scattering (GIWAXS) investigation. The crystal quality of perovskite films is significantly improved, resulting in single crystal‐like film. The best‐performing perovskite solar cells (PSCs) deliver a power conversion efficiency of 24.75%, resulting from the higher FF of 83.25% and an improved long‐term stability up to 3600 h. This work highlights the importance of purified phase transition path for the superior crystal quality toward high‐performance perovskite photovoltaics. [ABSTRACT FROM AUTHOR]

It is commonly believed that excess PbI2 has beneficial effects for perovskite solar cells owing to the modification of charge-transport behavior at interfaces, by surface passivation and by blocking electron-hole recombination. Here, we introduce a dynamically dispensed spin-coating technique in a two-step deposition to form a perovskite layer with controllable quantities of crystalline PbI2. Using this technique, the concentration of CH3NH3I solution is kept constant at the reaction interface, ensuring smooth growth of films. By changing the spinning rate during the reaction, the PbI2 conversion ratio and perovskite cuboid size can be optimized, resulting in a power conversion efficiency improvement over control devices. This dynamically dispensed technique represents a repeatable method for compositional control in perovskite solar cells and improves our understanding of how a PbI2 blocking layer improves the performance of perovskite solar cells. [ABSTRACT FROM AUTHOR]

The past five years have witnessed the significant breakthrough of perovskite solar cells (PSCs). High certificated power conversion efficiency (PCE) of 22.1% was achieved in a short time after the inorganic-organic perovskite was firstly used as the light absorber in the solar cells. It is believed that PSCs now become one of the most promising photovoltaic in the new-generation solar cells, which may rival silicon based solar cells. In this article, simplified planar perovskite solar cells without a hole-blocking layer were fabricated by a two-step spin-coating method, and the highest PCE of 15.1% was achieved with an average PCE of 13.6%. Moreover, it is found that the hysteresis effect is reduced in this kind of devices. The research on improved performance for the PSCs with simplified device architecture is very important both for understanding the working mechanism of cells, and for fabricating low-cost and high-performance PSCs to approach commercial applications. [ABSTRACT FROM AUTHOR]

It is commonly believed that excess PbI 2 has beneficial effects for perovskite solar cells owing to the modification of charge-transport behavior at interfaces, by surface passivation and by blocking electron-hole recombination. Here, we introduce a dynamically dispensed spin-coating technique in a two-step deposition to form a perovskite layer with controllable quantities of crystalline PbI 2 . Using this technique, the concentration of CH 3 NH 3 I solution is kept constant at the reaction interface, ensuring smooth growth of films. By changing the spinning rate during the reaction, the PbI 2 conversion ratio and perovskite cuboid size can be optimized, resulting in a power conversion efficiency improvement over control devices. This dynamically dispensed technique represents a repeatable method for compositional control in perovskite solar cells and improves our understanding of how a PbI 2 blocking layer improves the performance of perovskite solar cells., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A mixed halide perovskite of CH3NH3PbI(3-x)Cl(x) is synthesized via two-step sequential solution deposition by using a mixture of PbCl2 and PbI2 as the precursor to overcome the low solubility of pure PbCl2 with easy morphology control. 11.7% power conversion efficiency is achieved for the mesoscopic cell, much higher than the cell constructed via a spin-coating process.