It is imperative to develop a large-aspect-ratio grainbased thin film with low trap density for high-performance inorganic perovskite CsPbI 2 Br solar cells. Herein, by using Mn 2+ ion doping to modulate film growth, we achieved CsPbI 2 Br grains with aspect ratios as high as 8. It is found that Mn 2+ ions insert into the interstices of the CsPbI 2 Br lattice during the growth process, leading to suppressed nucleation and a decreased growth rate. The combination aids in the achievement of larger CsPbI 2 Br crystalline grains for increased J SC values as high as 14.37 mA/cm 2 and FFs as large as 80.0%. Moreover, excess Mn 2+ ions passivate the grain boundary and surface defects, resulting in effectively decreased recombination loss with improved hole extraction efficiency, which enhances the built-in electric field and hence increases V OC to 1.172 V. As a result, the champion device achieves stabilized efficiency as high as 13.47%, improved by 13% compared with only 11.88% for the reference device.

efficiency of laboratory-scale all-inorganic solar cells has been improved to 20.37%, [5] approaching ~70% of the efficiency limit based on the Shockley-Queisser (S-Q) theory. [9][10][11] Among all the high-performance all-inorganic perovskite devices, the photocurrent and fill factor have exceeded 95% and 90% of their theoretical S-Q limits, respectively, while the open-circuit voltage (V oc ) falls at ≈80% of the limit. Therefore, there is relatively larger room for improvement in the V oc for yielding higher power conversion efficiency (PCE). [5,[12][13][14][15] The V oc depends on the dynamics of charge carrier recombination, which is connected to the non-radiative recombination processes. [16][17][18][19] Defects usually scatter the carriers as non-radiative recombination reaction centers. [20][21][22][23] Therefore, preparing high-quality perovskite films with low-defect density is a prerequisite for high-performance photovoltaic devices. The quality of the perovskite active layer can be manipulated by the crystallization processes, thus dynamic control of crystallization appears to be very important. In a common solvent crystallization process, the perovskite grain growth is mainly completed in the initial solvent evaporation process because: 1) solvent evaporation leads to the super-saturation of the solute, producing a mass of seed crystals; 2) solvent evaporation drives the migration of the perovskite precursor colloids, which is beneficial to the grain growth. Subsequent extended annealing has faint effect on the grain growth. We assumed that if the "reactive solvent medium" can remain for a longer time, the colloids will react completely and the grains can merge better. Inspired by this idea, we consider molten salt (MS) synthesis, a classical method for preparing functional materials owing to its simplicity, speed, large-scale compatibility, and low cost. [24][25][26][27][28] The MS melts can exhibit homogeneous heat and mass transfer to carry out chemical transformation even at low temperature. [24,29] MS methods have been widely used in industrial production. For example, they are regarded as ideal reactors for the closed Th-U cycle due to their lower fissile inventory [30] and are applied in lignite pyrolysis to affect the products. [31] The MS processes have been applied not only in chemical reactions but also in material morphology manipulation. [32][33][34] So far, MS can be classified into two types: solid high-temperature MS, [27,34,35] and low-temperature MS (ionic liquids [ILs]) [32,36,37] depending on their states within a certain temperature range. The solid MSs show high ionic conductivity only in the liquid state, and thereby should be used at high temperatures above their melting points. ILs are considered Dynamic manipulation of crystallization is pivotal to the quality of polycrystalline films. A molten-salt-assisted crystallization (MSAC) strategy is presented to improve grain growth of the all-inorganic perovskite films. Compared with the traditional solvent annealing, MSAC enables...

Figure 10. a) Rotational distortion of [BX 6 ] 4− ([PbX 6 ] 4− ) octahedra by introducing smaller B-site cations. Reproduced with permission. [176] Copyright 2018, American Chemical Society. b) Schematic of the formation and stability of α-CsPbI3, γ-CsPbI 3 , and Ca 2+ -doped γ-CsPbI 3 . Reproduced with permission. [144] Copyright 2019, Wiley-VCH. c) The Mn 2+ doping modes by either forming a substitution or an intersitial. Reproduced with permission. [145] Copyright 2018, American Chemical Society. d) Energy band diagram of CsPb 1-x Ge x Br constructed from UV-vis and photoelectron yield spectroscopy measurement. Reproduced with permission. [146] Copyright 2018, Wiley-VCH.

pathway of the emerging perovskite solar cells (PSCs). [1][2][3][4] The defects in the bulk and at the surface of the perovskite lightharvesting material play vital roles in both the photoelectric conversion efficiency (PCE) and long-term stability. [5][6][7][8] These defects not only scatter charge carriers, giving rise to undesirable nonradiative recombination losses, [6,7] but also act as the predominant reactive sites for water and oxygen. Even worse, defects may serve as migration channels for ionic species that lead to device degradation. [7,[9][10][11] Thus, the presence of defects severely threatens the performance and stability of PSCs. Therefore, there have been numerous reports of efforts focused on lowering the defect density and deactivating defects. [4,[12][13][14][15][16][17][18][19][20][21][22] For effective/targeted defect passivation to further promote the performance of perovskite photovoltaic devices, it is imperative to carefully investigate the defect energy levels, defect types, and defect capturing capability. [6,23,24] Yang et al. characterized the defect energy distribution using admittance spectroscopy. [25] From those results combined with theoretical calculation, they attributed the defect with an activation energy of ≈0.16 eV above the valance band to iodine interstitials (I i ) in methylammonium lead Nonradiative losses caused by defects are the main obstacles to further advancing the efficiency and stability of perovskite solar cells (PSCs). There is focused research to boost the device performance by reducing the number of defects and deactivating defects; however, little attention is paid to the defect-capture capacity. Here, upon systematically examining the defect-capture capacity, highly polarized fluorinated species are designed to modulate the dielectric properties of the perovskite material to minimize its defectcapture radius. On the one hand, fluorinated polar species strengthen the defect dielectric-screening effect via enhancing the dielectric constant of the perovskite film, thus reducing the defect-capture radius. On the other, the fluorinated iodized salt replenishes the I-vacancy defects at the surface, hence lowering the defect density. Consequently, the power-conversion efficiency of an all-inorganic CsPbI 3 PSC is increased to as high as 20.5% with an opencircuit voltage of 1.2 V and a fill factor of 82.87%, all of which are among the highest in their respective categories. Furthermore, the fluorinated species modification also produces a hydrophobic umbrella yielding significantly improved humidity tolerance, and hence long-term stability. The present strategy provides a general approach to effectually regulate the defect-capture radius, thus enhancing the optoelectronic performance.

Polymeric hybrid sensors have garnered great interest in health monitoring, human−computer interaction, and soft robotics for their lightweight, flexibility, and feasible fabrication process. However, polymeric hybrid sensors suitable for harsh environments remain a considerable challenge, limiting further application. Herein, polyimide (PI)/carboxylated multi-walled carbon nanotube (c-MWCNT) hybrid aerogel fibers with a micro-porous structure were fabricated via wet-spinning and chemical thermal imidization. The fabricated PI/c-MWCNT hybrid aerogel fibers' conductivity and the change of current in response to the bending degree were tested, in which the relative current change achieved 4.78% with a bending degree of 150°. The fibers possessed a density of 0.41 ± 0.06 g/cm 3 , a conductivity of 17.8 ± 2.9 μS/m, and a tensile strength of 13.0 ± 1.1 MPa. In addition, they exhibited excellent heat/cold durability, whose decomposition temperature, cold resistance, and service life were 367 °C, −196 °C, and 300 cycles, respectively. Furthermore, the fabric sensor woven with PI/c-MWCNT hybrid aerogel fibers demonstrated two sensitivity stages of stage 1 (S 1 ) = 6.04 and stage 2 (S 2 ) = 0.55 under various pressures. Besides, it could be heated to 62 °C at a voltage of 30 V in 90 s with a changing resistance. The above properties demonstrate that the as-prepared fabric sensor exhibited great application potential for information acquisition and joule heating in harsh environments.