Advances and challenges to the commercialization of organic–inorganic halide perovskite solar cell technology

When transferring photovoltaic technologies from laboratory-scale fabrication to industrial applications, low cost, large area, high throughput, high solar-to-energy power conversion efficiency, long lifetime, and low toxicity are crucial attributes. In recent years, organic–inorganic halide perovskite solar cells have emerged as a promising high-performance, cost-effective solar cell technology. However, most of the best reported efficiencies have been obtained on small active-area devices (∼0.1 cm2). Therefore, development of protocols to industrialize such a technology is of paramount importance. In this article, we review the progress of perovskite solar cells with a particular emphasis on fabrication processes and instrumentation that have scale-up potential. For successful commercialization, the capacity to fabricate large-area modules is essential. Long-term stability is discussed, focusing on lifetime measurement and quantification protocols for commercialization. Cost-performance and life-cycle assessment analysis based on recently reported state-of-the-art perovskite solar cells are discussed. These analyses offer insights regarding required efficiency, module area size, and lifetime, in order for perovskite solar cells to be competitive with existing photovoltaic technologies. Finally, lead toxicity and possible solutions to this issue will be discussed. In the outlook, we outline future research directions based on reported results and trends in the field

Novel online data allocation for hybrid memories on tele-health systems

[EN] The developments of wearable devices such as Body Sensor Networks (BSNs) have greatly improved the capability of tele-health industry. Large amount of data will be collected from every local BSN in real-time. These data is processed by embedded systems including smart phones and tablets. After that, the data will be transferred to distributed storage systems for further processing. Traditional on-chip SRAMs cause critical power leakage issues and occupy relatively large chip areas. Therefore, hybrid memories, which combine volatile memories with non-volatile memories, are widely adopted in reducing the latency and energy cost on multi-core systems. However, most of the current works are about static data allocation for hybrid memories. Those mechanisms cannot achieve better data placement in real-time. Hence, we propose online data allocation for hybrid memories on embedded tele-health systems. In this paper, we present dynamic programming and heuristic approaches. Considering the difference between profiled data access and actual data access, the proposed algorithms use a feedback mechanism to improve the accuracy of data allocation during runtime. Experimental results demonstrate that, compared to greedy approaches, the proposed algorithms achieve 20%-40% performance improvement based on different benchmarks. (C) 2016 Elsevier B.V. All rights reserved.This work is supported by NSF CNS-1457506 and NSF CNS-1359557.Chen, L.; Qiu, M.; Dai, W.; Hassan Mohamed, H. (2017). Novel online data allocation for hybrid memories on tele-health systems. Microprocessors and Microsystems. 52:391-400. https://doi.org/10.1016/j.micpro.2016.08.003S3914005

Perovskite solar cells by vapor deposition based and assisted methods

Metal halide perovskite solar cells have made significant breakthroughs in power conversion efficiency and operational stability in the last decade, thanks to the advancement of perovskite deposition methods. Solution-based methods have been intensively investigated and deliver record efficiencies. On the other hand, vapor deposition-based and assisted methods were less studied in the early years but have received more attention recently due to their great potential toward large-area solar module manufacturing and high batch-to-batch reproducibility. In addition, an in-depth understanding of perovskite crystallization kinetics during the vapor deposition based and assisted process allows increasing perovskite deposition rate and enhancing perovskite quality. In this review, the advances in vapor-based and assisted methods for the fabrication of perovskite solar cells are introduced. The quality of the perovskite layers (i.e., morphology, crystallinity, defect chemistry, carrier lifetime) fabricated by different methods is compared. The limitations of state-of-the-art vapor-deposited perovskite layers are discussed. Finally, insights into the engineering of vapor deposition based and assisted perovskite layers toward efficient and stable perovskite solar cells and modules are provided

Progress of Surface Science Studies on ABX(3)-Based Metal Halide Perovskite Solar Cells

ABX(3) type metal halide perovskite solar cells (PSCs) have shown efficiencies over 25%, rocketing toward their theoretical limit. To gain the full potential of PSCs relies on the understanding of the device working mechanisms and recombination, the material quality, and the match of energy levels in the device stacks. In this review, the importance of designing PSCs from the viewpoint of surface/interface science studies is presented. For this purpose, recent case studies are discussed to demonstrate how probing of local heterogeneities (e.g., grains, grain boundaries, atomic structure, etc.) in perovskites by surface science techniques can help correlate material properties and PSC device performance. At the solar cell device level with active areas larger than millimeter scale, the ensemble average measurement techniques can characterize the overall average properties of perovskite films as well as their adjacent layers and provide clues to understand better the solar cell parameters. How generation and healing of electronic defects in perovskite films limit the device efficiency, reproducibility, and stability, and induce the time-dependent transient behavior in the current-voltage curves are also the central focus of this review. On the basis of these studies, strategies to further improve efficiency and stability, as well as reducing hysteresis are presented

Scalable Fabrication of Stable High Efficiency Perovskite Solar Cells and Modules Utilizing Room Temperature Sputtered SnO2 Electron Transport Layer

Stability and scalability have become the two main challenges for perovskite solar cells (PSCs) with the research focus in the field advancing toward commercialization. One of the prerequisites to solve these challenges is to develop a cost-effective, uniform, and high quality electron transport layer that is compatible with stable PSCs. Sputtering deposition is widely employed for large area deposition of high quality thin films in the industry. Here the composition, structure, and electronic properties of room temperature sputtered SnO2 are systematically studied. Ar and O-2 are used as the sputtering and reactive gas, respectively, and it is found that a highly oxidizing environment is essential for the formation of high quality SnO2 films. With the optimized structure, SnO2 films with high quality have been prepared. It is demonstrated that PSCs based on the sputtered SnO2 electron transport layer show an efficiency up to 20.2% (stabilized power output of 19.8%) and a T-80 operational lifetime of 625 h. Furthermore, the uniform and thin sputtered SnO2 film with high conductivity is promising for large area solar modules, which show efficiencies over 12% with an aperture area of 22.8 cm(2) fabricated on 5 x 5 cm(2) substrates (geometry fill factor = 91%), and a T-80 operational lifetime of 515 h

Hybrid chemical vapor deposition enables scalable and stable Cs-FA mixed cation perovskite solar modules with a designated area of 91.8 cm2 approaching 10% efficiency

The development of scalable deposition methods for stable perovskite layers is a prerequisite for the development and future commercialization of perovskite solar modules. However, there are two major challenges, i.e., scalability and stability. In sharp contrast to a previous report, here we develop a fully vapor based scalable hybrid chemical vapor deposition (HCVD) process for depositing Cs-formamidinium (FA) mixed cation perovskite films, which alleviates the problem encountered when using conventional solution coating of mainly methylammonium lead iodide (MAPbI3). Using our HCVD method, we fabricate perovskite films of Cs0.1FA0.9PbI2.9Br0.1 with enhanced thermal and phase stabilities, by the intimate incorporation of Cs into FA based perovskite films. In addition, the SnO2 electron transport layer (ETL) (prepared by sputter deposition) is found to be damaged during the HCVD process. In combination with precise interface engineering of the SnO2 ETL, we demonstrate relatively large area solar modules with efficiency approaching 10% and with a designated area of 91.8 cm2 fabricated on 10 cm × 10 cm substrates (14 cells in series). On the basis of our preliminary operational stability tests on encapsulated perovskite solar modules, we extrapolated that the T80 lifetime is approximately 500 h (under the light illumination of 1 sun and 25 °C)

Reduction of lead leakage from damaged lead halide perovskite solar modules using self-healing polymer-based encapsulation

In recent years, the major factors that determine commercialization of perovskite photovoltaic technology have been shifting from solar cell performance to stability, reproducibility, device upscaling and the prevention of lead (Pb) leakage from the module over the device service life. Here we simulate a realistic scenario in which perovskite modules with different encapsulation methods are mechanically damaged by a hail impact (modified FM 44787 standard) and quantitatively measure the Pb leakage rates under a variety of weather conditions. We demonstrate that the encapsulation method based on an epoxy resin reduces the Pb leakage rate by a factor of 375 compared with the encapsulation method based on a glass cover with an ultraviolet-cured resin at the module edges. The greater Pb leakage reduction of the epoxy resin encapsulation is associated with its optimal self-healing characteristics under the operating conditions and with its increased mechanical strength. These findings strongly suggest that perovskite photovoltaic products can be deployed with minimal Pb leakage if appropriate encapsulation is employed

The influence of secondary solvents on the morphology of a spiro-MeOTAD hole transport layer for lead halide perovskite solar cells

2,2 \u27,7,7 \u27-tetrakis(N,N-di-p-methoxyphenylamine)-9,9 \u27-spirobifluorene (spiro-MeOTAD) has been widely employed as a hole transport layer (HTL) in perovskite-based solar cells. Despite high efficiencies, issues have been reported regarding solution processed spiro-MeOTAD HTL such as pinholes and the strong dependence of electrical properties upon air exposure, which poses challenges for solar cell stability and reproducibility. In this work, we perform a systematic study to unravel the fundamental mechanisms for the generation of pinholes in solution-processed spiro-MeOTAD films. The formation of pinholes is closely related to the presence of small amounts of secondary solvents (e.g. H2O, 2-methyl-2-butene or amylene employed as a stabilizer, absorbed moisture from ambient, etc), which have low miscibility in the primary solvent generally used to dissolve spiro-MeOTAD (e.g. chlorobenzene). The above findings are not only applicable for spiro-MeOTAD (a small organic molecule), but also applicable to polystyrene (a polymer). The influence of secondary solvents in the primary solvents is the main cause for the generation of pinholes on film morphology. Our findings are of direct relevance for the reproducibility and stability in perovskite solar cells and can be extended to many other spin-coated or drop-casted thin films

Interface engineering strategies towards Cs2AgBiBr6 single-crystalline photodetectors with good Ohmic contact behaviours

Lead-free double perovskite materials have attracted much interest for optoelectronic applications due to their nontoxicity and high stability. In this work, centimetre-sized Cs2AgBiBr6 single crystals were successfully grown using methylammonium bromide (MABr) as the flux by a top-seeded solution growth (TSSG) method. The low-temperature crystal structure of Cs2AgBiBr6 single crystals was determined and refined. To investigate the interface problems between Cs2AgBiBr6 single crystals and electrodes, the optical band gap, X-ray photoelectron spectroscopy (XPS), and ultraviolet photoemission spectroscopy (UPS) measurements were performed on Cs2AgBiBr6 single crystals. More importantly, we investigated the photodetectors based on Cs2AgBiBr6 single crystals with different contact electrodes (Au, Ag, and Al). It is found that a good Ohmic contact with Ag electrodes enables excellent photo-response behaviors. Furthermore, we studied the photodetectors based on Cs2AgBiBr6 single crystals using Ag electrodes under room and low temperature conditions, which underwent phase transition. Cs2AgBiBr6 single crystal photodetectors show clear differences at room and low temperatures, which is caused by the work function changes of Cs2AgBiBr6 single crystals induced by the reversible phase transition. These attractive properties may enable opportunities to apply emerging double perovskite single-crystalline materials for high-performance optoelectronic devices

Inverse Growth of Large-Grain-Size and Stable Inorganic Perovskite Micronanowire Photodetectors

Control of forward and inverse reactions between perovskites and precursor materials is key to attaining high-quality perovskite materials. Many techniques focus on synthesizing nanostructured CsPbX3 materials (e.g., nanowires) via a forward reaction (CsX + PbX2 → CsPbX3). However, low solubility of inorganic perovskites and complex phase transition make it difficult to realize the precise control of composition and length of nanowires using the conventional forward approach. Herein, we report the self-assembly inverse growth of CsPbBr3 micronanowires (MWs) (CsPb2Br5 → CsPbBr3 + PbBr2↑) by controlling phase transition from CsPb2Br5 to CsPbBr3. The two-dimensional (2D) structure of CsPb2Br5 serves as nucleation sites to induce initial CsPbBr3 MW growth. Also, phase transition allows crystal rearrangement and slows down crystal growth, which facilitates the MW growth of CsPbBr3 crystals along the 2D planes of CsPb2Br5. A CsPbBr3 MW photodetector constructed based on the inverse growth shows a high responsivity of 6.44 A W–1 and detectivity of ∼1012 Jones. Large grain size, high crystallinity, and large thickness can effectively alleviate decomposition/degradation of perovskites, which leads to storage stability for over 60 days in humid environment (relative humidity = 45%) and operational stability for over 3000 min under illumination (wavelength = 400 nm, light intensity = 20.06 mW cm–2)