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Hybrid tin halides with formamidinium cations become a promising candidate for eco‐friendly solar cells, which achieves the best photovoltaic performance among various lead‐free perovskite solar cells (PSCs). Unfortunately, the low quality of perovskite layers and the oxidation of Sn2+ ions degrade the performance of devices, leading to an obviously lower power conversion efficiency (PCE) compare to hybrid lead halides. Additive engineering is a facile strategy for improving the quality of perovskite layers. In this work, the 2‐aminopyrazine (APZ) additive is investigated for depositing FA0.8PEA0.2SnI2.8Br0.2 layers, and corresponding PSCs are examined. It is found that the melting point of APZ additives drops below the annealing temperature of perovskite layers by the intermolecular interaction with formamidinium iodide (FAI). The melt phase at the grain boundaries encourages the diffusion of ions in the annealing process, leading to an improved quality of perovskite layers. And the formation of APZ‐SnI2 complex also inhibits the oxidation of Sn2+ ions. Consequently, the defect density and the recombination are significantly reduced in PSCs, resulting in an increase of PCEs from 11.4% to 13.0% and a simultaneous improvement of device stability. This work demonstrates a strategy for improving tin‐based PSCs based on melt assisted annealing and coordination interaction. [ABSTRACT FROM AUTHOR]

Organic–inorganic hybrid halide perovskites are highly promising candidates for efficient photovoltaics, however, the long-term stability in ambient air still limits their further practical applications. Herein, the enhancement of both performance and stability of perovskite solar cells is reported by employing two-dimension (2D)/three-dimension (3D) planar perovskite films. The 2D/3D planar perovskites combine the advantages of the high-performance from the 3D perovskite and the stability from 2D-perovskite. It is found that the benefits of the 2D perovskite are attributed to ultrathin coverage on the 3D perovskite surface, which not only passivates the grain boundaries of the underlayer 3D perovskite, but also aligns the energy level between the perovskite and hole transport layers from a microscopic point of view. This work demonstrates that modulating 2D/3D planar films by hybridizing different species of perovskite is a feasible way to simultaneously enhance both efficiency and stability of perovskite solar cells. Image 1 • The enhancement of both performance and stability of perovskite solar cells is reported. • 2D perovskite is formed by the reaction between PEAI and PbI 2 from 3D perovskite. • 2D/3D perovskite passivates grain boundaries and optimized energy band alignment. • Ultrathin 2D perovskite/3D perovskite layer exerts the function like the 2D:3D mixed layer. [ABSTRACT FROM AUTHOR]

Abstract A uniform and compact hole blocking layer is necessary for high-performance perovskite solar cells, since it not only serves as an electron collector but also suppresses the carrier recombination. So far, high efficient perovskite solar cells have been obtained by using a blocking layer TiO 2 that requires an additional TiCl 4 treatment. In this paper, a comprehensive understanding of TiCl 4 treatment on the TiO 2 layer was investigated in planar perovskite solar cells. Scanning electron microscope, atomic force microscope, and Kelvin probe force microscopy were applied to investigate the morphology of the TiCl 4 treated TiO 2 , and steady-state photo luminescence spectroscopy and electrical impedance spectroscopy were conducted to study charge carrier dynamics. The TiCl 4 treated TiO 2 layer can result in high efficiency over 20% in planar perovskite solar cells. Our results demonstrate that the TiCl 4 treatment on the compact TiO 2 prior to the perovskite deposition was necessary for achieving high-performance solar cells. Graphical abstract Image 1 Highlights • TiCl 4 treatment on the TiO 2 layer was investigated comprehensively. • TiCl 4 treatment fills the cracks and pinholes of the TiO 2 layer. • TiCl 4 treatment depresses the surface work function of the TiO 2 layer. • Perovskite solar cells with the TiCl 4 treated TiO 2 result in high efficiency over 20%. [ABSTRACT FROM AUTHOR]

• a-CsPbI 3 light harvester layers are prepared at low temperature without hydrogen iodide additive. • Lead acetate is used as the lead source of precursor solutions. • Ethylenediaminium iodide can cooperates with the lead acetate precursor. • The grain size of CsPbI 3 layers is increased and their trap density is reduced. • The power conversion efficiency and photo-stability of devices are improved. CsPbI 3 triggers strong interest in the photovoltaic community for their promising photoelectric property and nonvolatility. However, CsPbI 3 layers with a-phase crystal structure are difficult for preparation, and these layers easily degrade to non-photoactive δ-phase at room temperature. Tuning the composition of precursor solutions is an important method for improving the properties of CsPbI 3 layers. Herein, we prepare inorganic a-CsPbI 3 perovskite solar cells using lead acetate as the lead source, which is different from conventional precursors with lead iodide as the lead source. The lead acetate precursor needs neither incorporating hydrogen iodide nor preparing PbI 2 complex, and it is shown to enlarge the grain size, improve the crystallinity and reduce the trap density of CsPbI 3 layers. By cooperating the lead acetate precursor with EDAI 2 additive, the power conversion efficiency (PCE) of devices increases from 9.2% to 12.9% and the photo-stability of these devices is improved simultaneously. [ABSTRACT FROM AUTHOR]

For efficient perovskite solar cells (PSCs), hole transport layers (HTLs) are necessary components that can suppress recombination by collecting holes and blocking electrons. Inorganic hole transport materials (HTMs) are attractive because of their ease of preparation, low production cost and high stability. Although metal oxides and halides have been developed as the HTMs, metal hydroxides have not yet been reported as the HTMs of PSCs. In this work, copper doped lanthanum hydroxide (La x Cu y (OH) 3) nanorods were firstly synthesized by the hydrothermal method as a new kind of HTM for PSCs. Although the valence band edge of La(OH) 3 is slightly mismatch with that of perovskite layers, Cu2+ dopants improve the energy level alignment at HTL/perovskite interfaces. As an acceptor dopant for La(OH) 3 , Cu2+ ions also increase the hole transport ability of La x Cu y (OH) 3 HTLs. Additionally, La x Cu y (OH) 3 HTLs tend to encourage the crystallization of perovskite layers. As a consequence, Cu2+ dopants lead to an increase of PCE from 11.3 % to 20.4 % for La x Cu y (OH) 3 based PSCs. This promotion can be related to the reduced recombination process and the elevated charge extraction process. This work firstly applied metal hydroxide as the HTMs of PSCs, and demonstrates the regulation of these HTMs by the doping method. [Display omitted] • La(OH) 3 nanorods with copper dopants (La x Cu y (OH) 3) were synthesized. • La x Cu y (OH) 3 films were deposited by spin-coating at a low temperature of 100 °C. • Energy level and hole transport ability were improved by incorporating Cu2+ ions. • The Cu2+ dopants can also promote the crystallization of perovskite layers. • Cu2+ dopants lead to an improvement of PCEs from 11.3 % to 20.4 % for PSCs. [ABSTRACT FROM AUTHOR]

Electron transport layers can collect photo-generated electrons and suppress interfacial recombination, which are crucial for efficient perovskite solar cells. Tin oxide is a suitable electron transport material for its wide bandgap, high electron mobility, low photocatalytic activity and appropriate energy band offsets. For the deposition of tin oxide layers, SnCl 2 precursor is usually used for the conventional solution spin-coating method. In this work, we developed an in-situ synthesized precursor, and ultrathin tin oxide layers were obtained by the combustion process at 150 °C. Furthermore, the devices with these tin oxide layers can achieve the PCE of 19.6%, while conventional tin oxide layers with SnCl 2 precursor lead to the PCEs of 16.9% and 14.9% with and without plasma treatment. This improvement can be related to the enhanced photoelectron collection and superior interfacial contact. This work provides a facile method for fabricating SnO 2 electron transport layers of perovskite solar cells at low temperature. [Display omitted] • A novel SnO 2 precursor solution was developed by the in-situ synthesis from tin powder. • SnO 2 ETLs with high purity were prepared by the combustion process at low temperature. • Ultrathin SnO 2 ETLs were obtained with enhanced charge collection and interfacial contact. • PSCs with newly developed SnO 2 ETLs were superior to devices by conventional SnCl 2 precursor. [ABSTRACT FROM AUTHOR]