Recently, researchers have focused on the design of highly efficient flexible perovskite solar cells (PVSCs), which enables the implementation of portable and roll-to-roll fabrication in large scale. While NiOx is a promising material for hole transport layer (HTL) candidate for fabricating efficient PVSCs on a rigid substrate, the reported NiOx HTLs are formed using different multistep treatments (such as 300-500 °C annealing, O2-plasma, UVO, etc.), which hinders the development of flexible PVSCs based on NiOx. Meanwhile, the features of nanostructured morphology and flawless film quality are very important for the film to function as highly effective HTL of PVSCs. However, it is difficult to have the two features coexist natively, particularly in a solution process that flawless film will usually come with smooth morphology. Here, we demonstrate the flawless and surface-nanostructured NiOx film from a simple and controllable room-temperature solution process for achieving high performance flexible PVSCs with good stability and reproducibility. The power conversion efficiency (PCE) can reaches a promising value of 14.53% with no obvious hysteresis (and a high PCE of 17.60% for PVSC on ITO glass). Furthermore, the NiOx-based PVSCs show markedly improved air stability. Regarding the performance improvement, the flawless and surface-nanostructured NiOx film can make the interfacial recombination and monomolecular Shockley-Read-Hall recombination of PVSC reduce. In addition, the formation of an intimate junction of large interfacial area at NiOx film/the perovskite layer improve the hole extraction and thus PVSC performances. This work contributes to the evolution of flexible PVSCs with simple fabrication process and high device performances.

In the early stage, Marks and co-workers [ 13 ] reported a striking performance improvement of OSCs by replacing PEDOT:PSS with NiO x fi lm using a pulsed-laser deposition technology. From then on, NiO x HTLs have been reported for organic optoelectronics by various preparation methods, such as thermal evaporation, [ 14 ] sputtering, [ 9a ] and solution process. [ 9d , 15 ] Among them, solution process method is desirable for low-cost, large-scale and roll-to-roll production. Olson and co-workers [ 16 ] proposed a solution-processed NiO x fi lm as highly effi cient HTL in OSCs. The functional NiO x HTL was fabricated through annealing the precursor fi lm at a temperature of 275 °C. So and co-workers [ 17 ] also presented a NiO x fi lm by using monoethanolamine (MEA) to react with Ni in ethanol solution followed by thermally converting (275 °C) coordination complexes ions [Ni(MEA) 2 (OAc)]+ into high-quality NiO x . Meanwhile, solution-processed NiO x at 150 °C has also been realized. Ma and co-workers [ 18 ] reported a solution-processed NiO x fi lm for OSCs using oxygen-plasma treatment and annealing treatment simultaneously. Zhang et. al. reported that the colloidal NiO nanoparticles are used as the anode buffer layer in OSCs without high temperature post-annealing to induce decomposition and crystallization. [ 9f ] For a long period, the studies of NiO x HTLs were focused on utilizing sol-gel methods with thermally converting the precursor solution to NiO x thin fi lms. In the process of device fabrications, thermal annealing process and oxygen-plasma treatment may be simultaneously required, which hinders the applications of NiO x in fl exible optoelectronic devices. Instead of precursor method, an approach to signifi cantly reduce the processing temperature of TMO HTLs is to directly use high-quality colloidal nanoparticles (NPs). Jin and co-workers demonstrated a facile and general strategy based on ligand protection for the synthesis of unstable colloidal NiO nanocrystals. [ 19 ] Fattakhova-Rohlfi ng and co-workers described the preparation of ultrasmall, crystalline, and dispersible NiO nanoparticles, which are promising candidates as catalysts for electrochemical oxygen generation. [ 9e ] Herein, we will demonstrate a facile chemical precipitation method which is robust and simple for direct preparation of high-quality non-stoichiometric NiO x NPs. Remarkably, by using this method, NiO x HTL fi lm can be formed through a room-temperature solution process without any post-treatments during device fabrication. Interestingly, our results show that the NiO x NPs fi lm can function as effective HTLs over a wide range of annealing temperatures from room temperature to 150 °C. Very good optoelectronic performances utilizing the NiO x NPs fi lm as HTLs have been demonstrated in both OSCs and OLEDs. High power conversion effi ciency (PCE) of 9.16% (best 9.28%) was achieved in OSCs using NiO x

Entirely low‐temperature solution‐processed (≤100 °C) planar p‐i‐n perovskite solar cells (PSCs) offer great potential for commercialization of roll‐to‐roll fabricated photovoltaic devices. However, the stable inorganic hole‐transporting layer (HTL) in PSCs is usually processed at high temperature (200–500 °C), which is far beyond the tolerant temperature (≤150 °C) of roll‐to‐roll fabrication. In this context, inorganic NiOx nanoparticles (NPs) are an excellent candidate to serve as the HTL in PSCs, owing to their excellent solution processability at room temperature. However, the low‐temperature processing condition is usually accompanied with defect formation, which deteriorates the film quality and device efficiency to a large extent. To suppress this setback, we used a series of benzoic acid selfassembled monolayers (SAMs) to passivate the surface defects of the NiOx NPs and found that 4‐bromobenzoic acid could effectively play the role of the surface passivation. This SAM layer reduces the trap‐assisted recombination, minimizes the energy offset between the NiOx NPs and perovskite, and changes the HTL surface wettability, thus enhancing the perovskite crystallization, resulting in more stable PSCs with enhanced power conversion efficiency (PCE) of 18.4 %, exceeding the control device PCE (15.5 %). Also, we incorporated the above‐mentioned SAMs into flexible PSCs (F‐PSCs) and achieved one of the highest PCE of 16.2 % on a polyethylene terephthalate (PET) substrate with a remarkable power‐per‐weight of 26.9 W g−1. This facile interfacial engineering method offers great potential for the large‐scale manufacturing and commercialization of PSCs.

A new, all room-temperature solution process is developed to fabricate efficient, low-cost, and stable perovskite solar cells (PVSCs). The PVSCs show high efficiency of 17.10% and 14.19%, with no hysteresis on rigid and flexible substrates, respectively, which are the best efficiencies reported to date for PVSCs fabricated by room-temperature solution-processed techniques. The flexible PVSCs show a remarkable power-per-weight of 23.26 W g .

A simple off-the-shelf post-device ligand treatment is developed to simultaneously improve the performance and air stability of perovskite solar cells, as well as repair as-prepared ‘poor devices’ for the first time.

4211wileyonlinelibrary.com spin-coater are generally adopted for coating the silver nanowires on specifi c substrate. [13][14][15][16][17] However, the as-formed silver nanowire electrode would exhibit poor conductive and stability performances because of their large contact resistance. [ 18 ] The coating of additional material on silver nanowire fi lm, such as poly (3,4-ethylenedioxythiophene):polysty rene sulfonate (PEDOT:PSS), TiO 2 , ZnO, graphene, graphene oxide, carbon nanotube, etc., for welding the silver nanowires has been recently reported, [19][20][21][22][23][24][25][26][27][28] which will however alter the work function of the nanowire electrodes. Previous welding approaches without introducing different material with the nanowires would involve the assistance of heat, electrical current, mechanical pressure, and light, [ 13,18,[29][30][31][32][33][34][35] which will have concerns to meet the broad requirements in the emerging fl exible optoelectronic fi eld. Therefore, forming highly stable and conductive silver nanowire transparent electrode adaptable for versatile electrode applications (both anode and cathode) through simple, low-cost, and time-saving approach at room temperature and ambient condition would be highly desirable.The application of silver nanowires in organic solar cell (OSC), with its effi ciency rapidly improved recently, [36][37][38][39][40][41][42][43][44][45][46] would greatly benefi t the realization of all solution processed, lowcost, and fl exible device. However, in previous reports, thin silver nanowires with diameter smaller than 30 nm have been selected and utilized for bottom electrodes of OSCs, [47][48][49][50][51][52] since nanowire fi lm with relatively small surface roughness can be easily fl attened by traditional interfacial materials. Although silver nanowires with larger diameter are much more thermally and chemically stable, fewer studies have focused on their usage (e.g. 100 nm in diameter), as the increased surface roughness of the electrodes can lead to leakage current and deteriorated performance for thin fi lm optoelectronic devices if not properly addressed. Suppressing the surface roughness of nanowire electrodes with large diameter for practical optoelectronic device applications is still a challenging issue. At present, the methods reported for addressing the issue still involve mechanical pressing of silver nanowires or transferring silver nanowires into polymer matrix. [53][54][55] Developing simple and Locally Welded Silver Nano-Network Transparent Electrodes with High Operational Stability by a Simple Alcohol-Based Chemical ApproachHaifei Lu , Di Zhang , Jiaqi Cheng , Jian Liu , Jian Mao , and Wallace C. H . Choy *As an indispensable aspect of emerging fl exible optoelectronics, fl exible transparent electrodes, especially those comprised of metal nanowires, have attracted great attentions recently. Welding the nanowire junctions is an effective strategy for reducing the sheet resistance and improving the operational stability of fl exible nanowire...

While methylammonium lead iodide (MAPbI3) with interesting properties, such as a direct band gap, high and well-balanced electron/hole mobilities, as well as long electron/hole diffusion length, is a potential candidate to become the light absorbers in photodetectors, the challenges for realizing efficient perovskite photodetectors are to suppress dark current, to increase linear dynamic range, and to achieve high specific detectivity and fast response speed. Here, we demonstrate NiOx:PbI2 nanocomposite structures, which can offer dual roles of functioning as an efficient hole extraction layer and favoring the formation of high-quality MAPbI3 to address these challenges. We introduce a room-temperature solution process to form the NiOx:PbI2 nanocomposite structures. The nanocomposite structures facilitate the growth of the compact and ordered MAPbI3 crystalline films, which is essential for efficient photodetectors. Furthermore, the nanocomposite structures work as an effective hole extraction layer, which provides a large electron injection barrier and favorable hole extraction as well as passivates the surface of the perovskite, leading to suppressed dark current and enhanced photocurrent. By optimizing the NiOx:PbI2 nanocomposite structures, a low dark current density of 2 × 10(-10) A/cm(2) at -200 mV and a large linear dynamic range of 112 dB are achieved. Meanwhile, a high responsivity in the visible spectral range of 450-750 nm, a large measured specific detectivity approaching 10(13) Jones, and a fast fall time of 168 ns are demonstrated. The high-performance perovskite photodetectors demonstrated here offer a promising candidate for low-cost and high-performance near-ultraviolet-visible photodetection.

This study proposes a novel strategy of controllable deamination of Co–NH3 complexes in a system containing Ni(OH)2 to synthesize ultrasmall ternary oxide nanoparticles (NPs), NiCo2O4. Through this approach, ultrasmall (5 nm on average) and well‐dispersed NiCo2O4 NPs without exotic ligands are obtained, which enables the formation of uniform and pin‐hole free films. The tightly covered NiCo2O4 films also facilitate the formation of large perovskite grains and thus reduce film defects. The results show that with the NiCo2O4 NPs as the hole transport layer (HTL), the perovskite solar cells reach a high power conversion efficiency (PCE) of 18.23% and a promising stability (maintained ≈90% PCE after 500 h light soaking). To the best of the author's knowledge, it is the first time that spinel NiCo2O4 NPs have been applied as hole transport layer in perovskite solar cells successfully. This work not only demonstrates the potential applications of ternary oxide NiCo2O4 as HTLs in hybrid perovskite solar cells but also provides an insight into the design and synthesis of ultrasmall and ligand‐free NPs HTLs to enable cost‐effective photovoltaic devices.