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Additive is a conventional way to enhance halide perovskite active layer performance in multiaspects. Among them, π‐conjugated molecules have significantly special influence on halide perovskite due to the superior electrical conductivity, rigidity property, and good planarity of π‐electrons. In particular, π‐conjugated additives usually have stronger interaction with halide perovskites. Therefore, they help with higher charge mobility and longer device lifetime compared with alkyl‐based molecules. In this review, the detailed effect of conjugated molecules is discussed in the following parts: defect passivation, lattice orientation guidance, crystallization assistance, energy level rearrangement, and stability improvement. Meanwhile, the roles of conjugated ligands played in low‐dimensional perovskite devices are summarized. This review gives an in‐depth discussion about how conjugated molecules interact with halide perovskites, which may help understand the improved performance mechanism of perovskite device with π‐conjugated additives. It is expected that π‐conjugated organic additives for halide perovskites can provide unprecedented opportunities for the future improvement of perovskite devices.

Cs 2 AgBiBr 6 having a double perovskite structure is expected to be used in nonlead and stable optoelectronic devices and has received wide attention recently. At this stage, structures of optoelectronic devices using double perovskite and hybrid perovskite are the same. And the energy band structures of double perovskite and hybrid perovskite are different, which will cause energy-level mismatch in the device with double perovskite, which in turn will seriously restrict further improvement of the device performance. A strategy to solve this problem by constructing energy-level gradients with poly(3-hexylthiophene) (P3HT)/MoO 3 /poly[bis(4-phenyl)(2,4,6-trimethylphenyl)-amine] (PTAA) was reported for the first time. The construction of energy-level gradient is mainly achieved by P3HT and PTAA. MoO 3 plays a role in protecting the substrate (P3HT) and does not hinder hole transport because it is itself a p-type semiconductor. The champion power conversion efficiency of devices with P3HT/MoO 3 /PTAA is improved by more than a quarter compared to the standard devices. Moreover, in the champion device, the power conversion efficiency achieved 1.94% with a short-circuit current of 2.80 mA/cm 2 .

A long-persistent luminescence (LPL) material based on lead-free perovskite nanocrystals (Cs3In2Cl9 NCs) was synthesized by hot injection at 175 °C. Based on X-ray diffraction and theoretical calculations, the crystal structure of Cs3In2Cl9 NCs belongs to the trigonal space group R3̅c. The Cs3In2Cl9 NC powder emits white light at a peak wavelength of 430 nm with a full width at half maximum (FWHM) of about 118 nm and a photoluminescence quantum yield (PLQY) of 26.3%. The lifetime of its LPL is ∼1 s at 300 K and ∼10 s at 77 K. To explain the mechanism of LPL in Cs3In2Cl9, double self-defect states (DSDS) were proposed. To the best of our knowledge, this is the first time to obtain LPL in undoped lead-free perovskites. It promotes the application of perovskites and the explanation of the mechanism of LPL.

Organic−inorganic hybrid perovskites and double perovskites are both perovskite materials that have attracted much attention recently due to their excellent photoelectric properties. Hybrid perovskites have suitable band gaps but poor intrinsic stability. In contrast, double perovskites have a wide band gap but excellent stability. Therefore, we developed a strategy to modify hybrid-perovskite solar cells by utilizing double-perovskite (Cs 2 AgBi 0.1 In 0.9 Cl 6 ) nanocrystals to improve the stability of the devices. We have demonstrated that this strategy can effectively suppress nonradiative recombination, and reduce defects without affecting the absorption of the absorption layer. The performance and stability of MAPbI 3 solar cells fabricated by this strategy have been significantly improved. In addition, the FAPbI 3 solar cells prepared by this strategy show better performance, indicating that this strategy has a certain universality.

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Tin-based perovskites comprise one of the preferred nontoxic alternatives to Pb-based perovskites due to their desirable optoelectronic properties. However, there remains a crucial stability problem due to the property of Sn 2+ oxidation. In this study, we reported stable tin-based perovskite nanocrystals (NCs) using stannous acetate as the Sn 2+ source because of its stronger Sn−O bonding. To prevent the oxidation of Sn 2+ , a thin layer of CsBr coverage was formed in situ; tin-based perovskite NCs, Cs x SnBr x+2 @CsBr (1 < x < 4), show a high photoluminescence quantum yield (PLQY) of 78.2% and high stability. The measured lifetime of PLQY decrease to half of the initial value is ∼1287 h under ambient conditions and ∼2200 h under a nitrogen atmosphere, respectively. Furthermore, the as-fabricated lightemitting diodes based on Cs x SnBr x+2 @CsBr NCs as the emitting layer exhibit a maximum luminescence of 16 cd/m 2 and an external quantum efficiency of 0.035% with peaks at 451 and 615 nm, corresponding to the emissions of CsBr and Cs x SnBr x+2 , respectively. This work provided a new way to obtain stable Sn-based perovskite NCs and exhibited their potential for application in white lightemitting diodes (LEDs).

The performance degradation of perovskite solar cells (PSCs) under harsh environment (e.g., heat, moisture, light) is one of the greatest challenges for their commercialization. Herein, a conjugated sulfide 2-mercaptobenzimidazole (2MBI) is applied to significantly improve the photovoltaic properties and thermal stability of PSCs. When treated with heat, 2MBI cross-links with each other on the perovskite surface to facilitate charge transportation, suppress the escape of volatile species, and guide the rearrangement of surface perovskite grains. PSCs with 2MBI modification reach a PCE as high as 21.7% and maintain high-efficiency output during and after thermodestruction at 85 °C, while the unmodified ones suffer severe degradation. Unencapsulated devices after thermodestruction achieve over 98% of initial efficiency after 40-day storage under ambient conditions.