Identification of lead vacancy defects in lead halide perovskites.

Perovskite photovoltaics advance rapidly, but questions remain regarding point defects: while experiments have detected the presence of electrically active defects no experimentally confirmed microscopic identifications have been reported. Here we identify lead monovacancy (VPb) defects in MAPbI3 (MA = CH3NH3+) using positron annihilation lifetime spectroscopy with the aid of density functional theory. Experiments on thin film and single crystal samples all exhibited dominant positron trapping to lead vacancy defects, and a minimum defect density of ~3 × 1015 cm-3 was determined. There was also evidence of trapping at the vacancy complex [Formula: see text] in a minority of samples, but no trapping to MA-ion vacancies was observed. Our experimental results support the predictions of other first-principles studies that deep level, hole trapping, [Formula: see text], point defects are one of the most stable defects in MAPbI3. This direct detection and identification of a deep level native defect in a halide perovskite, at technologically relevant concentrations, will enable further investigation of defect driven mechanisms.

Oral health-related quality of life in oral cancer patients: systematic review and meta-analysis.

Aim: The purpose of this meta-analysis was to evaluate the impact of oral health on quality of life in oral cancer patients (OCPs). Methods: PubMed, Scopus and Web of Science databases were searched for publications on oral health-related quality of life (OHRQoL) in OCP and the information was extracted according to the PRISMA guidelines. A random effect model was used to obtain the pooled standard mean differences of Oral Health Impact Profile (OHIP)-14 questionnaire responses in meta-analysis. Results: total of 12 research papers were analyzed and revealed poor OHRQoL in OCPs (standard mean difference: 2.53; 95% CI: 1.55-3.50; p < 0.00001) compared with healthy individuals due to the effects of oncotherapy. Moreover, OHRQoL deteriorated with combinations of different treatment modalities. Conclusion: Oral health and oncotherapy can affect the quality of life in OCPs.

Recycling of Perovskite Films: Route toward Cost-Efficient and Environment-Friendly Perovskite Technology.

Mixed organic-inorganic halide perovskite solar cells have reached unprecedentedly high efficiency in a short term. Two major challenges in its large-scale deployment is the material instability and hazardous lead waste. Several studies have identified that lead replacement with its other alternatives does not show the similar assurance. In this manuscript, we introduce the concept of recycling of the degraded perovskite film (PbI2), gaining back the initial optoelectronic properties as the best possible solution to avoid lead waste. The simple recycling procedure allows the utilization of some of the most expensive (fluorine-doped tin oxide), primary energy-consuming (TiO2), and toxic (Pb) parts of the solar cell, reducing the payback time even further. This addresses the major issues of instability and expensive toxic lead disposal, altogether. We have demonstrated the comparative study of feasibility of recycling in degraded perovskite films deposited by three different standard fabrication routes. Films fabricated via acetate route shows efficient recycling compared to the other routes, i.e., chloride and sequential deposition routes. Moreover, recycling in sequentially deposited films needs further optimization.

Unraveling the Effect of Crystal Structure on Degradation of Methylammonium Lead Halide Perovskite.

Despite the remarkable efficiencies of perovskite solar cells, moisture instability has still been the major constraint in the technology deployment. Although, some research groups have discussed the possible mechanisms involved in the perovskite degradation, no broader understanding has been developed so far. Here, we demonstrate that the crystal orientation of perovskite film plays a major role in its degradation. We observed that the films fabricated via different routes led to different degradation behaviors and unraveled that diversity in the degradation rate arises due to the difference in crystallographic characteristics of the films. Using optical and electrical measurements, we show that the film prepared via a single-step (lead chloride precursor based) route undergoes a much faster degradation rate as compared with films prepared using single step (acetate precursor based) and two-step (or sequential deposition) routes. Although the resulting film is methylammonium lead iodide (MAPbI3) regardless of processing via different routes, their respective crystal orientation is different. In this manuscript, we correlate crystal orientation of MAPbI3 with their degradation pattern. Our studies also suggest a possible way to make stable perovskite film.

Partial oxidation of the absorber layer reduces charge carrier recombination in antimony sulfide solar cells.

We investigate the effect of a post heat treatment of the absorber layer in air for antimony sulfide (Sb2S3) sensitized solar cells. Phenomenologically, exposing the Sb2S3 surface of sensitised solar cells to air at elevated temperatures is known to improve device performance. Here, we have investigated the detailed origins of this improvement. To this end, samples were annealed in air for different time periods and the build-up of an antimony oxide layer was monitored by XPS. A very short heat treatment resulted in an increase in power conversion efficiency from η = 1.4% to η = 2.4%, while longer annealing decreased the device performance. This improvement was linked to a reduction in charge carrier recombination at the interface of Sb2S3 with the organic hole conductor, arising from the oxide barrier layer, as demonstrated by intensity modulated photovoltage spectroscopy (IMVS).

Efficient room temperature aqueous Sb2S3 synthesis for inorganic-organic sensitized solar cells with 5.1% efficiencies.

Sb2S3 sensitized solar cells are a promising alternative to devices employing organic dyes. The manufacture of Sb2S3 absorber layers is however slow and cumbersome. Here, we report the modified aqueous chemical bath synthesis of Sb2S3 absorber layers for sensitized solar cells. Our method is based on the hydrolysis of SbCl3 to complex antimony ions decelerating the reaction at ambient conditions, in contrast to the usual low temperature deposition protocol. This simplified deposition route allows the manufacture of sensitized mesoporous-TiO2 solar cells with power conversion efficiencies up to η = 5.1%. Photothermal deflection spectroscopy shows that the sub-bandgap trap-state density is lower in Sb2S3 films deposited with this method, compared to standard deposition protocols.

Ultrasmooth organic-inorganic perovskite thin-film formation and crystallization for efficient planar heterojunction solar cells.

To date, there have been a plethora of reports on different means to fabricate organic-inorganic metal halide perovskite thin films; however, the inorganic starting materials have been limited to halide-based anions. Here we study the role of the anions in the perovskite solution and their influence upon perovskite crystal growth, film formation and device performance. We find that by using a non-halide lead source (lead acetate) instead of lead chloride or iodide, the perovskite crystal growth is much faster, which allows us to obtain ultrasmooth and almost pinhole-free perovskite films by a simple one-step solution coating with only a few minutes annealing. This synthesis leads to improved device performance in planar heterojunction architectures and answers a critical question as to the role of the anion and excess organic component during crystallization. Our work paves the way to tune the crystal growth kinetics by simple chemistry.