Intermediate-phase engineering via dimethylammonium cation additive for stable perovskite solar cells.

Achieving the long-term stability of perovskite solar cells is arguably the most important challenge required to enable widespread commercialization. Understanding the perovskite crystallization process and its direct impact on device stability is critical to achieving this goal. The commonly employed dimethyl-formamide/dimethyl-sulfoxide solvent preparation method results in a poor crystal quality and microstructure of the polycrystalline perovskite films. In this work, we introduce a high-temperature dimethyl-sulfoxide-free processing method that utilizes dimethylammonium chloride as an additive to control the perovskite intermediate precursor phases. By controlling the crystallization sequence, we tune the grain size, texturing, orientation (corner-up versus face-up) and crystallinity of the formamidinium (FA)/caesium (FA)yCs1-yPb(IxBr1-x)3 perovskite system. A population of encapsulated devices showed improved operational stability, with a median T80 lifetime (the time over which the device power conversion efficiency decreases to 80% of its initial value) for the steady-state power conversion efficiency of 1,190 hours, and a champion device showed a T80 of 1,410 hours, under simulated sunlight at 65 °C in air, under open-circuit conditions. This work highlights the importance of material quality in achieving the long-term operational stability of perovskite optoelectronic devices.

Evaluating the effectiveness of an autism-specific public transport app for individuals on the autism spectrum: a pilot study.

PURPOSE: Autism is characterised by differences in social skills, limited communication abilities and repetitive behaviour, which often result in increased reliance on other people. Transportation is but one task that is commonly burdened on family members. Public transport is an inexpensive and widely available form of travel which facilitates independence. However, it presents unique challenges for individuals on the spectrum, as it requires complex skills including, but not limited to, understanding abstract information (e.g., maps, service schedules, etc.), problem-solving unexpected situations and timely management of transfers. As such, most individuals on the autism spectrum do not use public transport and have never considered using it. Here we evaluate the effectiveness of an autism-specific public transport app, OrienTrip, with autistic individuals and allied health professionals. METHODS: A total of 16 individuals on the autism spectrum (eight male and eight female participants) and 22 allied health professionals (19 females and three male participants) were recruited for the pilot study. RESULTS: We found that OrienTrip is effective in facilitating public transport use for autistic individuals. Individuals on the autism spectrum expressed their satisfaction with the app and agreed that it makes public transport easy to use. Similarly, allied health professionals also indicated that OrienTrip is helpful in assisting autistic individuals use public transport safely. CONCLUSION: Our findings demonstrate that OrienTrip can be used to facilitate independent travel for individuals on the autism spectrum using public transport. This can improve community participation opportunities for autistic individuals, including enhanced education, employment and social outcomes.Implications for rehabilitationIndividuals on the autism spectrum heavily rely on other people, namely family members, for their transportation needs.Public transport is an inexpensive and widely available form of travel which facilitates independence; however, it presents unique challenges for autistic individuals, as such, most individuals do not use it or consider using it.In this research, we have developed and evaluated one of the first autism-specific public transport mobile apps that facilitates independent public transport use.This tool can improve community participation opportunities for autistic individuals, including enhanced education, employment and social outcomes.

Route planning methods in indoor navigation tools for vision impaired persons: a systematic review.

OBJECTIVE: Route planning is key support, which can be provided by navigation tools for the blind and visually impaired (BVI) persons. No comprehensive analysis has been reported in the literature on this topic. The main objective of this study is to examine route planning approaches used by indoor navigation tools for BVI persons with respect to the route determination criteria, how user context is integrated, algorithms adopted, and the representation of the environment for route planning. METHODS: A systematic review was conducted covering the period 1982-July 2018 and thirteen databases. RESULTS: From the 1709 articles that resulted from the initial search, 131 were selected for the study. Route length was the sole factor used to determine the best route in the majority of the studies. Routes with less obstacles, less turns, more landmarks and close to walls were selected by the other studies. User variations were considered in few studies. Unique needs of the BVI persons were addressed by few novel algorithms which had integrated multiple parameters and BVI-friendly route modelling. CONCLUSION: Differences between the navigation capabilities of the sighted and the BVI community were not a major concern when deciding the optimum routes in the majority of BVI indoor navigation tools. How to trade-off between factors affecting optimum routes, and how to model suitable routes in complex buildings needs to be studied further, looking from the user perspective.Implications for rehabilitationNavigation differences between sighted and blind and vision-impaired (BVI) communities are not concerned frequently when planning routes in indoor navigation tools of BVI persons.Selecting routes avoiding areas difficult to traverse, close to walls, having landmarks, and less turns are some approaches used to address the unique needs of the BVI community.Assisting for recovery from veering and real-time obstacle detouring are useful features offered by these tools.Identifying and prioritizing different factors contributing to better routes, concerning user variations, and adopting multi-objective route optimization will help to develop improved route planning methodologies for BVI indoor navigation tool.

Public transport planning tool for users on the autism spectrum: from concept to prototype.

PURPOSE: This research explored the challenges of public transport use for individuals on the autism spectrum. It, subsequently, proposed a mobile application solution, coproduced by individuals on the autism spectrum, to facilitate public transport use. METHODS: We, first, conducted a review of the literature to highlight the challenges people on the autism spectrum face when utilizing public transport. We, then, designed a list of mobile application functionalities that address the identified problems. To validate these functionalities, 27 young autistic adults and 19 families of autistic individuals were employed. Finally, based on the findings, we designed a mobile application that helps facilitate public transport use for those on the autism spectrum. RESULTS: We found that the most prevalent concerns, in public transport use, amongst autistic individuals and their families are safety and spatial awareness. Specific problems include finding one's way to the bus stop, boarding the correct service and disembarking at the correct stop. Interestingly, anxiety about unexpected events was also a barrier. Sensory sensitivity, similarly, was found to be an obstacle. CONCLUSIONS: This study defined the challenges of public transport use for autistic individuals and proposed a technological solution. The findings can also inform innovators, public transport providers and policymakers to improve public transport accessibility.Implications for rehabilitationPeople on the autism spectrum heavily rely on other individuals, namely family and friends, for their transportation needs. This dependence results in immobility for the autistic individuals and significant time and economical sacrifice for the person responsible for the transportation.Public transport, a cheap and widely available form of transportation, has not yet been clearly studied with individuals on the autism spectrum.We clearly define the challenges of using public transport and put forward a trip planner mobile application, coproduced by autistic individuals, that facilitate it.In the long term, this enhanced travel independence can lead to greater education and employment opportunities and an overall improved quality of life.

Observation of Charge Generation via Photoinduced Stark Effect in Mixed-Cation Lead Bromide Perovskite Thin Films.

Extensive transient absorption studies on hybrid organic-inorganic lead halide perovskites have elucidated many optical properties important for their device performance. Despite the enormous progress, the derivative shaped photoinduced absorption feature in transient spectra that is above the bandgap has many explanations, including the photoinduced Stark effect, where the bandgap is blue shifted due to a local electric field generated by charges. In this work, we employ broad band transient absorption and two-dimensional electronic spectroscopy (2DES) to examine the early transient events after photoexcitation of [CH(NH2)2]0.83Cs0.17PbBr3 (FA0.83Cs0.17PbBr3). 2DES resolves a photomodulation feature at the excitation energy of the exciton, suggesting the presence of a dipole field created by a polaron pair shifting the exciton transition to higher energies. As this polaron pair dissociates over 200 fs, the exciton transition shifts to higher energies over the same time scale, evidenced by the 2DES diagonal energy spectra. Given that the observations are well explained in terms of the Stark effect, our work provides extra grounds to support the Stark effect assignment of the above-gap photoinduced absorption. Furthermore, our study reports on the time scale of charge generation, contributing to the fundamental understanding of mixed-cation lead bromide perovskite photophysics.

Access to all components of scanned mathematical documents by vision-impaired students.

Vision-impaired people access documents using screen readers. Electronic documents may contain non-textual components, non-linear components, and multidimensional components, such as mathematical expressions and graphs. These components create a number of accessibility issues for those who use screen readers as assistive technology. The research presented here describes mathematical information retrieval, and accessible and navigable representation of mathematical function graphs as solutions to these issues. Additionally, this research study is about how to present course materials to vision-impaired students, and is not about how to teach them. The system shows promise, given an initial evaluation by a vision-impaired person, and an encouraging review by three blind professionals. The next step is to perform a full evaluation of the system employing a larger number of vision-impaired students.

A generic interface to reduce the efficiency-stability-cost gap of perovskite solar cells.

A major bottleneck delaying the further commercialization of thin-film solar cells based on hybrid organohalide lead perovskites is interface loss in state-of-the-art devices. We present a generic interface architecture that combines solution-processed, reliable, and cost-efficient hole-transporting materials without compromising efficiency, stability, or scalability of perovskite solar cells. Tantalum-doped tungsten oxide (Ta-WO x )/conjugated polymer multilayers offer a surprisingly small interface barrier and form quasi-ohmic contacts universally with various scalable conjugated polymers. In a simple device with regular planar architecture and a self-assembled monolayer, Ta-WO x -doped interface-based perovskite solar cells achieve maximum efficiencies of 21.2% and offer more than 1000 hours of light stability. By eliminating additional ionic dopants, these findings open up the entire class of organics as scalable hole-transporting materials for perovskite solar cells.

Crystallization Kinetics and Morphology Control of Formamidinium-Cesium Mixed-Cation Lead Mixed-Halide Perovskite via Tunability of the Colloidal Precursor Solution.

The meteoric rise of the field of perovskite solar cells has been fueled by the ease with which a wide range of high-quality materials can be fabricated via simple solution processing methods. However, to date, little effort has been devoted to understanding the precursor solutions, and the role of additives such as hydrohalic acids upon film crystallization and final optoelectronic quality. Here, a direct link between the colloids concentration present in the [HC(NH2 )2 ]0.83 Cs0.17 Pb(Br0.2 I0.8 )3 precursor solution and the nucleation and growth stages of the thin film formation is established. Using dynamic light scattering analysis, the dissolution of colloids over a time span triggered by the addition of hydrohalic acids is monitored. These colloids appear to provide nucleation sites for the perovskite crystallization, which critically impacts morphology, crystal quality, and optoelectronic properties. Via 2D X-ray diffraction, highly ordered and textured crystals for films prepared from solutions with lower colloidal concentrations are observed. This increase in material quality allows for a reduction in microstrain along with a twofold increase in charge-carrier mobilities leading to values exceeding 20 cm2 V-1 s-1 . Using a solution with an optimized colloidal concentration, devices that reach current-voltage measured power conversion efficiency of 18.8% and stabilized efficiency of 17.9% are fabricated.

Controlling Nucleation and Growth of Metal Halide Perovskite Thin Films for High-Efficiency Perovskite Solar Cells.

Metal halide perovskite thin films can be crystallized via a broad range of solution-based routes. However, the quality of the final films is strongly dependent upon small changes in solution composition and processing parameters. Here, this study demonstrates that a fractional substitution of PbCl2 with PbI2 in the 3CH3 NH3 I:PbCl2 mixed-halide starting solution has a profound influence upon the ensuing thin-film crystallization. The presence of PbI2 in the precursor induces a uniform distribution of regular quadrilateral-shaped CH3 NH3 PbI3 perovskite crystals in as-cast films, which subsequently grow to form pinhole-free perovskite films with highly crystalline domains. With this new formulation of 3CH3 NH3 I:0.98PbCl2 :0.02PbI2 , this study achieves a 19.1% current-voltage measured power conversion efficiency and a 17.2% stabilized power output in regular planar heterojunction solar cells.

Efficient and Air-Stable Mixed-Cation Lead Mixed-Halide Perovskite Solar Cells with n-Doped Organic Electron Extraction Layers.

Air-stable doping of the n-type fullerene layer in an n-i-p planar heterojunction perovskite device is capable of enhancing device efficiency and improving device stability. Employing a (HC(NH2 )2 )0.83 Cs0.17 Pb(I0.6 Br0.4 )3 perovskite as the photoactive layer, glass-glass laminated devices are reported, which sustain 80% of their "post burn-in" efficiency over 3400 h under full sun illumination in ambient conditions.

Perovskite-perovskite tandem photovoltaics with optimized band gaps.

We demonstrate four- and two-terminal perovskite-perovskite tandem solar cells with ideally matched band gaps. We develop an infrared-absorbing 1.2-electron volt band-gap perovskite, FA0.75Cs0.25Sn0.5Pb0.5I3, that can deliver 14.8% efficiency. By combining this material with a wider-band gap FA0.83Cs0.17Pb(I0.5Br0.5)3 material, we achieve monolithic two-terminal tandem efficiencies of 17.0% with >1.65-volt open-circuit voltage. We also make mechanically stacked four-terminal tandem cells and obtain 20.3% efficiency. Notably, we find that our infrared-absorbing perovskite cells exhibit excellent thermal and atmospheric stability, not previously achieved for Sn-based perovskites. This device architecture and materials set will enable "all-perovskite" thin-film solar cells to reach the highest efficiencies in the long term at the lowest costs.

A mixed-cation lead mixed-halide perovskite absorber for tandem solar cells.

Metal halide perovskite photovoltaic cells could potentially boost the efficiency of commercial silicon photovoltaic modules from ∼20 toward 30% when used in tandem architectures. An optimum perovskite cell optical band gap of ~1.75 electron volts (eV) can be achieved by varying halide composition, but to date, such materials have had poor photostability and thermal stability. Here we present a highly crystalline and compositionally photostable material, [HC(NH2)2](0.83)Cs(0.17)Pb(I(0.6)Br(0.4))3, with an optical band gap of ~1.74 eV, and we fabricated perovskite cells that reached open-circuit voltages of 1.2 volts and power conversion efficiency of over 17% on small areas and 14.7% on 0.715 cm(2) cells. By combining these perovskite cells with a 19%-efficient silicon cell, we demonstrated the feasibility of achieving >25%-efficient four-terminal tandem cells.