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  1. Abstract

    2D black phosphorene (BP) carries a stellar set of physical properties such as conveniently tunable bandgap and extremely high ambipolar carrier mobility for optoelectronic devices. Herein, the judicious design and positioning of BP with tailored thickness as dual‐functional nanomaterials to concurrently enhance carrier extraction at both electron transport layer/perovskite and perovskite/hole transport layer interfaces for high‐efficiency and stable perovskite solar cells is reported. The synergy of favorable band energy alignment and concerted cascade interfacial carrier extraction, rendered by concurrent positioning of BP, delivered a progressively enhanced power conversion efficiency of 19.83% from 16.95% (BP‐free). Investigation into interfacial engineering further reveals enhanced light absorption and reduced trap density for improved photovoltaic performance with BP incorporation. This work demonstrates the appealing characteristic of rational implementation of BP as dual‐functional transport material for a diversity of optoelectronic devices, including photodetectors, sensors, light‐emitting diodes, etc.

     
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  2. Abstract

    Tailoring the doping of semiconductors in heterojunction solar cells shows tremendous success in enhancing the performance of many types of inorganic solar cells, while it is found challenging in perovskite solar cells because of the difficulty in doping perovskites in a controllable way. Here, a small molecule of 4,4′,4″,4″′‐(pyrazine‐2,3,5,6‐tetrayl) tetrakis (N,N‐bis(4‐methoxyphenyl) aniline) (PT‐TPA) which can effectively p‐dope the surface of FAxMA1−xPbI3(FA: HC(NH2)2; MA: CH3NH3) perovskite films is reported. The intermolecular charge transfer property of PT‐TPA forms a stabilized resonance structure to accept electrons from perovskites. The doping effect increases perovskite dark conductivity and carrier concentration by up to 4737 times. Computation shows that electrons in the first two layers of octahedral cages in perovskites are transferred to PT‐TPA. After applying PT‐TPA into perovskite solar cells, the doping‐induced band bending in perovskite effectively facilitates hole extraction to hole transport layer and expels electrons toward cathode side, which reduces the charge recombination there. The optimized devices demonstrate an increased photovoltage from 1.12 to 1.17 V and an efficiency of 23.4% from photocurrent scanning with a stabilized efficiency of 22.9%. The findings demonstrate that molecular doping is an effective route to control the interfacial charge recombination in perovskite solar cells which is in complimentary to broadly applied defect passivation techniques.

     
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  3. Stabilizing perovskite solar cells requires consideration of all defective sites in the devices. Substantial efforts have been devoted to interfaces, while stabilization of grain boundaries received less attention. Here, we report on a molecule tributyl(methyl)phosphonium iodide (TPI), which can convert perovskite into a wide bandgap one-dimensional (1D) perovskite that is mechanically robust and water insoluble. Mixing TPI with perovskite precursor results in a wrapping of perovskite grains with both grain surfaces and grain boundaries converted into several nanometer-thick 1D perovskites during the grain formation process as observed by direct mapping. The grain wrapping passivates the grain boundaries, enhances their resistance to moisture, and reduces the iodine released during light soaking. The perovskite films with wrapped grains are more stable under heat and light. The best device with wrapped grains maintained 92.2% of its highest efficiency after light soaking under 1-sun illumination for 1900 hours at 55°C open-circuit condition.

     
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  4. Understanding carrier recombination processes in metal halide perovskites is fundamentally important to further improving the efficiency of perovskite solar cells, yet the accurate recombination velocity at grain boundaries (GBs) has not been determined. Here, we report the determination of carrier recombination velocities at GBs (SGB) of polycrystalline perovskites by mapping the transient photoluminescence pattern change induced by the nonradiative recombination of carriers at GBs. Charge recombination at GBs is revealed to be even stronger than at surfaces of unpassivated films, with averageSGBreaching 2200 to 3300 cm/s. Regular surface treatments do not passivate GBs because of the absence of contact at GBs. We find a surface treatment using tributyl(methyl)phosphonium dimethyl phosphate that can penetrate into GBs by partially dissolving GBs and converting it into one-dimensional perovskites. It reduces the averageSGBby four times, with the lowestSGBof 410 cm/s, which is comparable to surface recombination velocities after passivation.

     
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  5. Despite the high-efficiency and low-cost prospect for perovskite solar cells, great concerns of lead toxicity and instability remain for this technology. Here, we report an encapsulation strategy for perovskite modules based on lead-adsorbing ionogel, which prevents lead leakage and withstand long-term stability tests. The ionogel layers integrated on both sides of modules enhance impact resistance. The self-healable ionogel can prevent water permeation into the perovskite layer and adsorb lead that might leak. The encapsulated devices pass the damp heat and thermal cycling accelerated stability tests according to International Electrotechnical Commission 61215 standard. The ionogel encapsulation reduces lead leakage to undetectable level after the hail-damaged module is soaked in water for 24 hours. Even being rolled over by a car followed by water soaking for 45 days, the ionogel encapsulation reduces lead leakage by three orders of magnitude. This work provides a strategy to simultaneously address lead leakage and stability for perovskite modules. 
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  6. Placing plasmonic nanoparticles (NPs) in close proximity to semiconductor nanostructures renders effective tuning of the optoelectronic properties of semiconductors through the localized surface plasmon resonance (LSPR)-induced enhancement of light absorption and/or promotion of carrier transport. Herein, we report on, for the first time, the scrutiny of carrier dynamics of perovskite solar cells (PSCs) via sandwiching monodisperse plasmonic/dielectric core/shell NPs with systematically varied dielectric shell thickness yet fixed plasmonic core diameter within an electron transport layer (ETL). Specifically, a set of Au NPs with precisely controlled dimensions ( i.e. , fixed Au core diameter and tunable SiO 2 shell thickness) and architectures (plain Au NPs and plasmonic/dielectric Au/SiO 2 core/shell NPs) are first crafted by capitalizing on the star-like block copolymer nanoreactor strategy. Subsequently, these monodisperse NPs are sandwiched between the two consecutive TiO 2 ETLs. Intriguingly, there exists a critical dielectric SiO 2 shell thickness, below which hot electrons from the Au core are readily injected to TiO 2 ( i.e. , hot electron transfer (HET)); this promotes local electron mobility in the TiO 2 ETL, leading to improved charge transport and increased short-circuit current density ( J sc ). It is also notable that the HET effect moves up the Fermi level of TiO 2 , resulting in an enhanced built-in potential and open-circuit voltage ( V oc ). Taken together, the PSCs constructed by employing a sandwich-like TiO 2 /Au NPs/TiO 2 ETL exhibit both greatly enhanced J sc and V oc , delivering champion PCEs of 18.81% and 19.42% in planar and mesostructured PSCs, respectively. As such, the judicious positioning of rationally designed monodisperse plasmonic NPs in the ETL affords effective tailoring of carrier dynamics, thereby providing a unique platform for developing high-performance PSCs. 
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