Flexible perovskite solar cells (f‐PSCs) have attracted great attention because of their unique advantages in lightweight and portable electronics applications. However, their efficiencies are far inferior to those of their rigid counterparts. Herein, a novel histamine diiodate (HADI) is designed based on theoretical study to modify the SnO2/perovskite interface. Systematic experimental results reveal that the HADI serves effectively as a multifunctional agent mainly in three aspects: 1) surface modification to realign the SnO2 conduction band upward to improve interfacial charge extraction; 2) passivating the buried perovskite surface, and 3) bridging between the SnO2 and perovskite layers for effective charge transfer. Consequently, the rigid MA‐free PSCs based on the HADI‐SnO2 electron transport layer (ETL) display not only a high champion power conversion efficiency (PCE) of 24.79% and open‐circuit voltage (VOC) of 1.20 V but also outstanding stability as demonstrated by the PSCs preserving 91% of their initial efficiencies after being exposed to ambient atmosphere for 1200 h without any encapsulation. Furthermore, the solution‐processed HADI‐SnO2 ETL formed at low temperature (100 °C) is utilized in f‐PSCs that achieve a PCE as high as 22.44%, the highest reported PCE for f‐PSCs to date.

over 80% in the visible light range. [2] ITO is widely used as essential transparent conducting electrodes in flat panel displays, touch screens, and solar cells. The global ITO market has an annual growth rate of 15% and is valued at 7 billion USD in 2019. In 2004, Nomura and Hosono et al. made great breakthrough in oxide thin film transistor (TFT) based on amorphous indium gallium zinc oxide (IGZO) grown at room temperature. [3] The amorphous IGZO showed an impressive mobility of 9 cm 2 V −1 s −1 , about 10 times of amorphous hydrogenated Si TFT which was used exclusively for displays at that time. Soon after Hosono's seminal work, IGZO TFT was commercialized by Sharp Corporation in 2012, and then rapidly expanded to mobile phones, tablets and laptops. [4] In 2019, the fifth generation IGZO TFT went to mass production, capable of driving large-area displays (85 in.) with ultrahigh 8 K resolution. [5] Moreover, oxide TFTs are also considered as the most promising transistors for next-generation curved, flexible, or even rollable electronics. [6] The great success of oxide semiconductors is underpinned by their unique electronic structure, amenability for n-type doping, as well as intrinsic stability. Oxide semiconductors have bandgap larger than 3 eV, enabling transparency in the visible spectrum. The conduction band (CB) of oxide semiconductors is typically composed of empty ns-orbitals (n ≥ 4) of heavy posttransition metals. The large, spherical ns-orbitals give rise to a high electron mobility even in amorphous phases, as well as high dopability for hosting a high density of electrons. Therefore, oxide semiconductors are amendable via doping to be a transparent semiconductor or a transparent conductor, depending on the purposes of device applications, e.g., TFT or ITO. However, there are two sides to every coin. The nature of electronic structure of oxide semiconductors also leads to the fundamental limitation of achieving p-type oxide semiconductors, which is exacerbated by the presence of a high background electron density arising from the formation of unintentional defects and impurities. [1a,7] The lack of p-type semiconductor significantly limits the great potential of oxide electronics. [7b] A high electron density and defect states cause detrimental effects on oxide TFT device performance, such as a high off-current, lower mobility, and instability issues. [8] In the past two decades, considerable research efforts have been made to understand the microscopic origin of defect states and background electrons Wide bandgap oxide semiconductors constitute a unique class of materials that combine properties of electrical conductivity and optical transparency. They are being widely used as key materials in optoelectronic device applications, including flat-panel displays, solar cells, OLED, and emerging flexible and transparent electronics. In this article, an up-to-date review on both the fundamental understanding of materials physics of oxide semiconductors, and recent research progress on design of new...

results declare that DL-treated PSCs have the well operational stability against harsh conditions, such as light illumination, humidity, and heat.

The remarkable high PCE of hybrid PSCs relies on the unique advantages of perovskite materials (high light-absorption coefficient, [7] broad lightabsorption range, [8] fast charge-carrier mobility, [9] long diffusion length, [10] tunable bandgap, [11] small exciton binding energy, [12] etc.) and effective structural and surface modifications (compositional engineering, interfacial passivation, additive engineering, etc.). [13][14][15][16] Perovskites based on FA x MA 1−x PbI 3 (FA, formamidinium; MA, methylammonium) have been widely applied in hybrid PSCs due to their lower bandgap and higher solar light-harvesting efficiency in contrast to MAPbI 3 . [17][18][19][20][21] Compared with FAPbI 3 , partial substitution of FA (ionic radius = 2.79 Å) with MA (ionic radius = 2.17 Å) could improve the stability of hybrid PSCs due to the reduced tolerance factor to the appropriate range (0.8-1). [22,23] However, the low-boilingpoint MA cations easily escape from the perovskite lattice during the device fabrication process, and the large FA cations are impeded from embedding into the MA vacancies due to their weak interaction with the established lattice, both of which lead to many defects (MA/FA vacancies, undercoordinated Pb 2+ , and Pb I antisites) at the surface and interface of the perovskite. [24][25][26] Those defects always act as non-radiative recombination Formamidinium methylammonium lead iodide (FAMAPbI 3 ) perovskite has been intensively investigated as a potential photovoltaic material because it has higher phase stability than its pure FAPbI 3 perovskite counterpart. However, its power conversion efficiency (PCE) is significantly inferior due to its high density of surface detects and mismatched energy level with electrodes. Herein, a bifunctional passivator, methyl haloacetate (methyl chloroacetate, (MClA), methyl bromoacetate (MBrA)), is designed to reduce defect density, to tune the energy levels and to improve interfacial charge extraction in the FAMAPbI 3 perovskite cell by synergistic passivation of both CO groups and halogen anions. As predicted by modeling undercoordinated Pb 2+ , the MBrA shows a very strong interaction with Pb 2+ by forming a dimer complex ([C 6 H 10 Br 2 O 4 Pb] 2+ ), which effectively reduces the defect density of the perovskite and suppresses non-radiative recombination. Meanwhile, the Br − in MBrA passivates iodine-deficient defects. Consequently, the MBrA-modified device presents an excellent PCE of 24.29%, an open-circuit voltage (V oc ) of 1.18 V (V oc loss ≈ 0.38 V), which is one of the highest PCEs among all FAMAPbI 3 -based perovskite solar cells reported to date. Furthermore, the MBrA-modified devices without any encapsulation exhibit remarkable long-term stability with only 9% of PCE loss after exposure to ambient air for 1440 h.