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There is a growing demand for the flexible and bendable power sources that can be applied to the curved surfaces such as car dashboards, building walls, smart phones, Internet of Things (IoTs), Bluetooth, Wi-Fi, and wearable devices. Consequently, intensive studies have been done to develop flexible, bendable, and even stretchable solar cells. Organic-inorganic hybrid perovskite solar cells (OIHP-SCs) are particularly attractive owing to their unique properties such as high absorption coefficient, convenient bandgap tunability, small exciton binding energy, fair intrinsic flexibility, and solution processability. [1][2][3][4][5][6][7][8][9][10][11] As Kojima et al. reported on a liquid-junction CH 3 NH 3 PbX 3 (MAPbX 3 , X ¼ halogen) OIHP-sensitized solar cells, researchers have made great efforts to develop highly efficient OIHP-SCs and recently attained 25.5% of record efficiency at 1 Sun condition (AM1.5G 100 mW cm À2 ) using rigid glass-based OIHP-SCs with small active area. [12,13] Therefore, the OIHP-SCs can produce power densities of several tens μW cm À2 from indoor and %20 mW cm À2 from outdoor light conditions, and thus provide sufficient power for the IoT sensors, wireless communication devices, and wearable devices that require 1-1000 mW of power and flexibility.So far, most flexible OIHP-SCs have been fabricated as either n-i-p or p-i-n device architectures with a transparent conducting oxide (TCO) electrode such as indium tin oxide (ITO). To begin with, in 2013 Kumar et al. reported on one of the first n-i-p-type flexible OIHP-SCs on a polyethylene terephthalate (PET)/ITO substrate with a power conversion efficiency (PCE) of 2.6%. [14] With further development in 2020, Chung et al. demonstrated a high PCE of 20.75% using a device structure of polyethylene naphthalate (PEN)/ITO/SnO 2 /porous Zn 2 SnO 4 / (FAPbI 3 ) 0.95 (MAPbBr 3 ) 0.05 /spiro-OMeTAD (2,2 0 ,7,7 0 -tetrakis[N, N-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene)/Au. [27] However, as n-i-p type devices are inherently vulnerable to ambient moisture due to the presence of additives in the topexposed hole transport material (HTM), many studies have attempted to mimic the high efficiency of n-i-p devices by using p-i-n-type flexible OIHP-SCs. One of the pioneering works for flexible p-i-n-type OIHP-SC devices with a PCE of 6.4% was realized by Docampo et al. in 2013 using a PET/ITO substrate. [28]

Enhancement in weak-light detection and other photodetection properties was observed for organic–inorganic halide perovskite photodetectors as a result of benzylammonium iodide (BzAI) treatment at the methylammonium lead triiodide (MAPbI3) and hole-transport layer (HTL) interface. After treatment, growth of the two-dimensional Ruddlesden–Popper perovskite phase was observed at the MAPbI3 surface, which shifted the overall surface work function upwards and thus effectively facilitated charge transfer across the MAPbI3/HTL interface. As a result, the fully fabricated device with 10 mg/mL (BzAI/isopropanol) treatment exhibited shorter rise time (t rise) and decay time (t decay) of 53 and 38 μs, respectively, compared to t rise and t decay of 214 and 120 μs, respectively, for the pristine MAPbI3 sample. In addition, the BzAI-treated device exhibited larger linearity compared to the pristine MAPbI3 sample, demonstrating a high and stable specific detectivity of 1.49 × 1013 to 2.14 × 1013 Jones under incident light intensity of 10–3 to 100 mW/cm2, respectively.

Spray-coating is a scalable and time-efficient technique for the development of large-area metal halide perovskite (MHP) solar cells. However, a bottleneck still exists toward the development of fully scalable n-i-p-type MHP solar cells particularly on spray-coating the hole transporting layer (HTL). Here, we present a reliable strategy of spray-coating the HTL by using MoO2 nanoparticles with small amounts of poly­(triarylamine) (PTAA) binders to ensure uniform coverage and efficient charge extraction. By spray-coating all layers except the Au electrode, we achieve high and scalable efficiencies of 14.26 and 13.88% for CsPbI2Br unit cells (0.12 cm2) and submodules (25 cm2), respectively. We then extend toward an all-spray-coating process by spray-coating carbon black as the top counter electrode, resulting in a submodule efficiency of 10.08%. Finally, we also demonstrate good long-term stability of the submodules under damp heat conditions (85 °C/85% relative humidity) over 1000 h.

In designing efficient perovskite solar cells (PSCs), the selection of suitable electron transport layers (ETLs) is critical to the final device performance as they determine the driving force for selective charge extraction. SnO2 nanoparticles (NPs) based ETLs have been a popular choice for PSCs due to superior electron mobility, but their relatively deep‐lying conduction band energy levels (ECB) result in substantial potential loss. Meanwhile, TiO2 NPs establish favorable band alignment owing to shallower ECB, but their low intrinsic mobility and abundant surface trap sites impede the final performance. For this reason, constructing a cascaded bilayer ETL is highly desirable for efficient PSCs, as it can rearrange energy levels and exploit on advantages of an individual ETL. In this study, we prepare SnO2 NPs and acetylacetone‐modified TiO2 (Acac‐TiO2) NPs and implement them as bilayer SnO2/Acac‐TiO2 (BST) ETL, to assemble cascaded energy band structure. SnO2 contributes to rapid charge carrier transport from high electron mobility while Acac‐TiO2 minimizes band‐offset and effectively suppresses interfacial recombination. Accordingly, the optimized BST ETL generates synergistic influence and delivers power conversion efficiency (PCE) as high as 23.14% with open‐circuit voltage (VOC) reaching 1.14 V. Furthermore, the BST ETL is transferred to a large scale and the corresponding mini module demonstrates peak performance of 18.39% PCE from 25 cm2 aperture area. Finally, the BST‐based mini module exhibit excellent stability, maintaining 83.1% of its initial efficiency after 1000 h under simultaneous 1 Sun light‐soaking and damp heat (85 °C/RH 85%) environment.