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Recently, lead‐free double perovskites have emerged as a promising environmentally friendly photovoltaic material for their intrinsic thermodynamic stability, appropriate bandgaps, small carrier effective masses, and low exciton binding energies. However, currently no solar cell based on these double perovskites has been reported, due to the challenge in film processing. Herein, a first lead‐free double perovskite planar heterojunction solar cell with a high quality Cs2AgBiBr6 film, fabricated by low‐pressure assisted solution processing under ambient conditions, is reported. The device presents a best power conversion efficiency of 1.44%. The preliminary efficiency and the high stability under ambient condition without encapsulation, together with the high film quality with simple processing, demonstrate promise for lead‐free perovskite solar cells.

An oligothiophene derivative named DR3TBDTT with high hydrophobicity was synthesized and functioned as the hole transporting material without an ion additive. 8.8% of power conversion efficiency was obtained for CH3NH3PbI3-xClx based planar solar cells with improved stability, compared to devices using Li-TFSI doped spiro-MeOTAD.

In high performance perovskite based solar cells, CH3NH3PbI3 is the key material. We carried out a study on charge diffusion in spin-coated CH3NH3PbI3 perovskite thin film by transient fluorescent spectroscopy. A thickness-dependent fluorescent lifetime was found. By coating the film with an electron or hole transfer layer, [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) or 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (Spiro-OMeTAD) respectively, we observed the charge transfer directly through the fluorescence quenching. One-dimensional diffusion model was applied to obtain long charge diffusion distances in thick films, which is ~1.7 μm for electrons and up to ~6.3 μm for holes. Short diffusion distance of few hundreds of nanosecond was also observed in thin films. This thickness dependent charge diffusion explained the formerly reported short charge diffusion distance (~100 nm) in films and resolved its confliction to thick working layer (300–500 nm) in real devices. This study presents direct support to the high performance perovskite solar cells and will benefit the devices’ design.

While the super fluorescence quenching capacity of graphene and graphene oxide (GO) has been extensively employed to develop fluorescent sensors, their own unique fluorescence and its potential for chemo-/biosensing have seldom been explored. Here we report a GO-based photoinduced charge transfer (PCT) label-free near-infrared (near-IR) fluorescent biosensor for dopamine (DA). The multiple noncovalent interactions between GO and DA and the ultrafast decay at the picosecond range of the near-IR fluorescence of GO resulted in effective self-assembly of DA molecules on the surface of GO, and significant fluorescence quenching, allowing development of a PCT-based biosensor with direct readout of the near-IR fluorescence of GO for selective and sensitive detection of DA. The developed method gave a detection limit of 94 nM and a relative standard deviation of 2.0% for 11 replicate detections of 2.0 μM DA and was successfully applied to the determination of DA in biological fluids with quantitative recovery (98-115%).

Recently, highly efficient solar cells based on organic-inorganic perovskites have been intensively reported for developing fabricating methods and device structures. Additional power conversion efficiency should be gained without increasing the thickness and the complexity of the devices to accord with practical applications. In this paper, a rough interface between perovskite and HTM was fabricated in perovskite solar cells to enhance the light scattering effect and improve the charge transport. The parameters related to the morphology have been systematically investigated by sequential deposition. Simultaneous enhancements of short-circuit current and power conversion efficiency were observed in both CH₃NH₃PbI₃ and CH₃NH₃PbI₃-xClx devices containing the rough interface, with power conversion efficiencies of 10.2% and 10.8%, respectively. Our finding provides an efficient and universal way to control the morphology and further optimize perovskite solar cells for devices by sequential deposition with various structures.

Considering the remarkable progress in photovoltaic performance, scholars have focused on perovskite solar cells (PSCs) over the recent two years. TiO 2 thin film is a semiconductor with a wide band gap and is usually used as an electronselective layer (ESL) in PSCs. Although SnO 2 exhibits conductivity higher than that of TiO 2 , its use as a compact ESL in PSCs has not been reported. In this study, nanocrystalline SnO 2 thin film was prepared through a sol−gel method and then characterized. The prepared SnO 2 thin film was composed of small tetragonal rutile nanocrystals. We applied the SnO 2 compact ESL into PSCs and compared their performance with that of PSCs based on a TiO 2 thin layer. SnO 2 -ESL-based PSCs (S-PSCs) showed higher short-circuit current density and lower open-circuit voltage, fill factor, and conversion efficiency than the conventional TiO 2 -ESL-based PSCs. Furthermore, the photovoltaic performance of S-PSCs was highly dependent on measurement means, and this relationship was investigated and is discussed in detail.

Objective Rapid, reliable, and easy-to-implement diagnostics that can be adapted in early SARS-CoV-2 diagnosis are critical to combat the epidemic. SARS-CoV-2 nucleocapsid protein (NP) is an ideal target for viral antigen-based detection. A rapid and convenient method was developed based on fluorescence immunochromatographic (FIC) assay to detect the SARS-CoV-2 NP antigen. However, the accuracy of this diagnostic method needs to be examined. Methods This prospective study was carried out between February 10 and 15, 2020 in 7 hospitals of Wuhan and 1 hospital of Chongqing, China. Participants with clinically suspected SARS-CoV-2 infection were enrolled. NP antigen testing by FIC assay and nucleic acid (NA) testing by RT-PCR were performed simultaneously in a blind manner with the same nasopharyngeal swab sample. The diagnostic accuracy of NP antigen testing was calculated by taking NA testing of RT-PCR as reference standard, in which samples with cycle threshold (Ct) value ≤ 40 were interpreted as SARS-CoV-2 positives. Results A total of 253 participants were enrolled and 2 participants were excluded from the analyses due to invalid NP testing results. Of 251 participants (99.2%) that were included in the diagnostic accuracy analysis, a total of 201 participants (80.1%) had a Ct value ≤40. With Ct value 40 as the cut-off of NA testing, the sensitivity, specificity, and percent agreement of the FIC assay was 75.6% (95% CI 69.0%-81.3%), 100% (95% CI 91.1%-100%), and 80.5% (95% CI 75.1%-84.9%), respectively. Conclusions With RT-PCR assay as reference standard, NP antigen testing by FIC assay shows high specificity and relative high sensitivity in SARS-CoV-2 diagnosis in the early phase of infection.