The stabilization of black-phase formamidinium lead iodide (α-FAPbI3) perovskite under various environmental conditions is considered necessary for solar cells. However, challenges remain regarding the temperature sensitivity of α-FAPbI3 and the requirements for strict humidity control in its processing. Here we report the synthesis of stable α-FAPbI3, regardless of humidity and temperature, based on a vertically aligned lead iodide thin film grown from an ionic liquid, methylamine formate. The vertically grown structure has numerous nanometer-scale ion channels that facilitate the permeation of formamidinium iodide into the lead iodide thin films for fast and robust transformation to α-FAPbI3. A solar cell with a power-conversion efficiency of 24.1% was achieved. The unencapsulated cells retain 80 and 90% of their initial efficiencies for 500 hours at 85°C and continuous light stress, respectively.

An efficient electron transport layer (ETL) plays a key role in promoting carrier separation and electron extraction in planar perovskite solar cells (PSCs). An effective composite ETL is fabricated using carboxylic‐acid‐ and hydroxyl‐rich red‐carbon quantum dots (RCQs) to dope low‐temperature solution‐processed SnO2, which dramatically increases its electron mobility by ≈20 times from 9.32 × 10−4 to 1.73 × 10−2 cm2 V−1 s−1. The mobility achieved is one of the highest reported electron mobilities for modified SnO2. Fabricated planar PSCs based on this novel SnO2 ETL demonstrate an outstanding improvement in efficiency from 19.15% for PSCs without RCQs up to 22.77% and have enhanced long‐term stability against humidity, preserving over 95% of the initial efficiency after 1000 h under 40–60% humidity at 25 °C. These significant achievements are solely attributed to the excellent electron mobility of the novel ETL, which is also proven to help the passivation of traps/defects at the ETL/perovskite interface and to promote the formation of highly crystallized perovskite, with an enhanced phase purity and uniformity over a large area. These results demonstrate that inexpensive RCQs are simple but excellent additives for producing efficient ETLs in stable high‐performance PSCs as well as other perovskite‐based optoelectronics.

Tin halide perovskites attract incremental attention to deliver lead‐free perovskite solar cells. Nevertheless, disordered crystal growth and low defect formation energy, related to Sn(II) oxidation to Sn(IV), limit the efficiency and stability of solar cells. Engineering the processing from perovskite precursor solution preparation to film crystallization is crucial to tackle these issues and enable the full photovoltaic potential of tin halide perovskites. Herein, the ionic liquid n‐butylammonium acetate (BAAc) is used to tune the tin coordination with specific O…Sn chelating bonds and NH…X hydrogen bonds. The coordination between BAAc and tin enables modulation of the crystallization of the perovskite in a thin film. The resulting BAAc‐containing perovskite films are more compact and have a preferential crystal orientation. Moreover, a lower amount of Sn(IV) and related chemical defects are found for the BAAc‐containing perovskites. Tin halide perovskite solar cells processed with BAAc show a power conversion efficiency of over 10%. This value is retained after storing the devices for over 1000 h in nitrogen. This work paves the way toward a more controlled tin‐based perovskite crystallization for stable and efficient lead‐free perovskite photovoltaics.

Daily temperature variations induce phase transitions and lattice strains in halide perovskites, challenging their stability in solar cells. We stabilized the perovskite black phase and improved solar cell performance using the ordered dipolar structure of β-poly(1,1-difluoroethylene) to control perovskite film crystallization and energy alignment. We demonstrated p-i-n perovskite solar cells with a record power conversion efficiency of 24.6% over 18 square millimeters and 23.1% over 1 square centimeter, which retained 96 and 88% of the efficiency after 1000 hours of 1-sun maximum power point tracking at 25° and 75°C, respectively. Devices under rapid thermal cycling between −60° and +80°C showed no sign of fatigue, demonstrating the impact of the ordered dipolar structure on the operational stability of perovskite solar cells.

The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adma.202107850.

efficiency (PCE) of rigid-substrate-based devices has exceeded 25%. [2] Meanwhile, flexible devices have also reached the highest PCE of 21.05%. [3] The merits of PSCs, such as low cost, suitable bandgaps for indoor light sources such as lightemitting diodes (LEDs), and simply fabricating flexible devices, [4][5][6][7] also enhance the indoor commercialization possibility. [8] In the past several years, research on indoor photovoltaics has also accelerated, which promotes the realization of the idea of the indoor Internet of Things (IoT) in the future. [9] The surfaces of indoor small electronic devices are usually irregularly curved. Compared to devices with rigid substrates, flexible devices can better fit the surface of small electrical appliances, which can increase the effective functional area and widen the application field range. [10] As the demand for adaptation to various indoor application scenarios, the mechanical stability of flexible devices is a very important concern. [11][12][13][14] Herein, we get inspiration from the balloon glue. The reason that balloon glue can deform so sharply but not break contributes to the cross-linking agent borax (Na 2 B 4 O 7 ). Borax is a common crosslinking agent that has excellent flexibility. The oxygen ion groups at both sides of the molecule can form stronger coordination bonds with lead than the lead-iodine bond, thereby acting as a stretch bridge at grain boundaries of perovskite films. We conducted physical tensile tests and extreme temperature variation tests (−180 to 150 °C) on the optimized films and found that the treated films exhibited better mechanical stability and phase stability. To prove the indoor application prospects of flexible devices, we first systematically reported the trap density of states of flexible devices under different light intensities. It is found that the trap density of formamidinium-lead-iodide (FAPbI 3 )-based perovskite is reduced after optimization, which is more suitable for indoor applications. [15,16] Meanwhile, since the improved film formation quality of perovskite contributed to passivation treatment of borax, the champion PCE of optimized rigid and flexible PSCs reached 23.05% and 21.63%, respectively, under AM 1.5G illumination. Moreover, the flexible device presents an a superior indoor PCE of 31.85% under 1062 lux (LED, 2956 K), which is currently the best flexible perovskite indoor photovoltaic device.Perovskite photovoltaics are strong potential candidates to drive low-power off-grid electronics for indoor applications. Compared with rigid devices, flexible perovskite devices can provide a more suitable surface for indoor small electronic devices, enabling them have a broader indoor application prospect. However, the mechanical stability of flexible perovskite photovoltaics is an urgent issue solved. Herein, a kind of 3D crosslinking agent named borax is selected to carry out grain boundary penetration treatment on perovskite film to realize full-dimensional stress release. This strategy improves the mechanical a...

Flexible perovskite solar cells (FPSCs) represent a promising technology in the development of next-generation photovoltaic and optoelectronic devices. SnO 2 electron transport layers (ETL) typically undergo significant cracking during the bending process of FPSCs, which can significantly compromise their charge transport properties. Herein, the semi-planar non-fullerene acceptor molecule Y6 (BT-core-based fused-unit dithienothiophen [3,2-b]-pyrrolobenzothiadiazole derivative) is introduced as the buffer layer for SnO 2 -based FPSCs. It is found that the Y6 buffer layer can enhance the ability of charge extraction and bending stability for SnO 2 ETL. Moreover, the internal stress of perovskite films is also reduced. As a result, SnO 2 /Y6-based FPSCs achieved a power conversion efficiency (PCE) of 20.09% and retained over 80% of their initial efficiency after 1000 bending cycles at a curvature radius of 8 mm, while SnO 2 -based devices only retain 60% of their initial PCE (18.60%) upon the same bending cycles. In addition, the interfacial charge extraction is also effectively improved in conjunction with reduced defect density upon incorporation of Y6 on the SnO 2 ETL, as revealed by femtosecond transient absorption (Fs-TA) measurements.

State‐of‐the‐art, high‐performance formamidinium‐lead‐iodide‐based (FAPbI3‐based) perovskite photovoltaics are mainly prepared by one‐step antisolvent dripping deposition or two‐step sequential fabrication methods. Compared with the one‐step deposition, the two‐step fabricated perovskite films tend to grow columnar perovskite grains vertically which is easier for carrier extraction and transportation. Herein, the concept of formamidinium methylammonium cesium based ternary‐cation two‐step sequential deposition method is put forward by incorporating cesium acetate (CsAc) into a lead iodide precursor, which generates CsPbI3 crystal nuclei improving the further perovskite crystallization. When the formamidinium/methylammonium‐based organic amine salts solution is spin coated on the PbI2 substrate, the acetate moves upward and induces perovskite orientational and uniform crystallization, which can go a step further for the vertical columnar grains achieving fewer defects and higher photovoltaic efficiency. The champion outdoor power conversion efficiency of the modified device under AM 1.5G reaches 21.50% and its indoor efficiency at 1000 lux reaches 40.99%. This work paves the way for further exploring ternary‐cation two‐step sequential deposition methods to prepare high‐performance perovskite photovoltaics.