The stability of a perovskite solar cell (PSC) is enhanced significantly by applying a customized thin-film encapsulation (TFE). The TFE is composed of a multilayer stack of organic/inorganic layers deposited by initiated chemical vapor deposition and atomic layer deposition, respectively, whose water vapor transmission rate is on the order of 10−4 g m−2 d−1 at an accelerated condition of 38 °C and 90% relative humidity (RH). The TFE is optimized, taking into consideration various aspects of thermosensitive PSCs. Lowering the process temperature is one of the most effective methods for minimizing the thermal damage to the PSC during the monolithic integration of the TFE onto PSC. The direct deposition of TFE onto a PSC causes less than 0.3% degradation (from 18.5% to 18.2%) in the power conversion efficiency, while the long-term stability is substantially improved; the PSC retains 97% of its original efficiency after a 300 h exposure to an accelerated condition of 50 °C and 50% RH, confirming the enhanced stability of the PSC against moisture. This is the first demonstration of a TFE applied directly onto PSCs in a damage-free manner, which will be a powerful tool for the development of highly stable PSCs with high efficiency.

　In Sn-based halide perovskite solar cells (PSCs), the oxidation of Sn2+ to Sn4+ under ambient air leads to unwanted p-type doping in the perovskite film, which is a main reason for increased background carrier density and low efficiency. Here, we find that the introduction of bromide into formamidinium tin iodide (CH(NH2)2SnI3, FASnI3) lattice significantly lowers the carrier density of perovskite absorber, which is thought to be a result of reduction of Sn vacancies. It reduces the leakage current of devices, increases recombination lifetime, and finally improves open-circuit voltage and fill factor of the resulting devices employing mesoporous TiO2 as an electron transport layer. Consequently, a high power conversion efficiency (PCE) of 5.5% is achieved with an average PCE of 5%, and after encapsulation the devices are highly stable over 1000 h under continuous one sun illumination including the ultraviolet region. This study suggests a simple approach for improving stability and efficiency in FASnI3-based PSCs.

　Successful commercialization of perovskite solar cells (PSCs) in the near future will require the fabrication of cells with high efficiency and long-term stability. Despite their good processability at low temperatures, the majority of organic conductors employed in the fabrication of high-efficiency PSCs [e.g., 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (spiro-OMeTAD) and poly(triaryl amine) (PTAA)] have low thermal stability. In order to fabricate PSCs with excellent thermal stability, both the constituent material itself and the interface between the constituents must be thermally stable. In this work, we focused on copper phthalocyanine (CuPC) as a model hole-transporting material (HTM) for thermally stable PSCs since CuPC is known to possess excellent thermal stability and interfacial bonding properties. The CuPC-based PSCs recorded a high power conversion efficiency (PCE) of ∼18% and maintained 97% of their initial efficiency for more than 1000 h of thermal annealing at 85 °C. Moreover, the device was stable under thermal cycling tests (50 cycles, −45 to 85 °C). The high PCE and high thermal stability observed in the CuPC-PSCs were found to arise as a result of the strong interfacial and conformal coating present on the surface of the perovskite facets, located between CuPC and the perovskite layer. These results will provide an important future direction for the development of highly efficient and thermally stable PSCs.

　The formation of a dense and uniform thin layer on the substrates is crucial for the fabrication of high-performance perovskite solar cells (PSCs) containing formamidinium with multiple cations and mixed halide anions. The concentration of defect states, which reduce a cell’s performance by decreasing the open-circuit voltage and short-circuit current density, needs to be as low as possible. We show that the introduction of additional iodide ions into the organic cation solution, which are used to form the perovskite layers through an intramolecular exchanging process, decreases the concentration of deep-level defects. The defect-engineered thin perovskite layers enable the fabrication of PSCs with a certified power conversion efficiency of 22.1% in small cells and 19.7% in 1-square-centimeter cells.

　Perovskite solar cells (PSCs) exceeding a power conversion efficiency (PCE) of 20% have mainly been demonstrated by using mesoporous titanium dioxide (mp-TiO2) as an electron-transporting layer. However, TiO2 can reduce the stability of PSCs under illumination (including ultraviolet light). Lanthanum (La)–doped BaSnO3 (LBSO) perovskite would be an ideal replacement given its electron mobility and electronic structure, but LBSO cannot be synthesized as well-dispersible fine particles or crystallized below 500°C. We report a superoxide colloidal solution route for preparing a LBSO electrode under very mild conditions (below 300°C). The PSCs fabricated with LBSO and methylammonium lead iodide (MAPbI3) show a steady-state power conversion efficiency of 21.2%, versus 19.7% for a mp-TiO2 device. The LBSO-based PSCs could retain 93% of their initial performance after 1000 hours of full-Sun illumination.

　Photoresponsive change in the basal spacing of cationic azo dye-layered silicate intercalation compounds was investigated using X-ray diffraction under controlled humidity conditions to investigate the mechanism of the photoresponse triggered by trans–cis photoisomerization. The molecular design of azo dyes was conducted and two cationic azo dyes (phenylazobenzene and phenylazonaphthalene) were used to obtain intercalation compounds with different packing and hydration. Whereas the trans-phenylazobenzene-layered silicate hardly adsorbed water vapor, the trans-phenylazonaphthalene intercalation compound strongly interacted with water. Both azo dyes photoisomerized in the interlayer space reversibly. Under the relative humidity of 95%, the basal spacing of the phenylazobenzene–silicate increased upon UV irradiation, confirming that the change in the basal spacing was caused by the photoinduced hydration. Under the relative humidity of 6.8%, the basal spacing of the phenylazonaphthalene–silicate decreased upon UV irradiation, suggesting that the packing of the phenylazonaphthalene in the interlayer space was changed to be compacted by the photochemical conversion to the cis-form.

　We have designed and synthesized fluorinated indolo[3,2-b]indole (IDID) derivatives as crystalline hole-transporting materials (HTM) for perovskite solar cells. The fluorinated IDID backbone enables a tight molecular arrangement stacked by strong π–π interactions, leading to a higher hole mobility than that of the current HTM standard, p,p-spiro-OMeTAD, with a spherical shape and amorphous morphology. Moreover, the photoluminescence quenching in a perovskite/HTM film is more effective at the interface of the perovskite with IDIDF as compared to that of p,p-spiro-OMeTAD. As a consequence, the device fabricated using IDIDF shows superior photovoltaic properties compared to that using p,p-spiro-OMeTAD, exhibiting an optimal performance of 19%. Thus, this remarkable result demonstrates IDID core-based materials as a new class of HTMs for highly efficient perovskite solar cells.

　Development of fast and intuitive detection techniques for explosive vapors is highly desired for security applications. Among those techniques, fluorescence quenching has advantages in terms of portability and maintenance cost compared to electrically driven platforms. One of the challenging issues is the restricted sensitivity (i.e., low initial quenching and quenching saturation) caused by hindered diffusion of gaseous analytes inside a dense, solid film, and resulting limited surface area, where the target molecules are reacting. Here, multilevel 3D porous nanostructures are introduced, which possess strong fluorescence and enhanced sensing abilities, produced by a rapid and scalable lithographic technique. The cyanostilbene fluorophore with low-absorption around patterning wavelengths (≈355 nm) is newly designed to be incorporated into transparent photopolymer. The emission color and intensity of the composite films under excitation can be precisely controlled by adjusting the concentration of fluorophore based on intermolecular effects. The patterned, monolithic film with low-volume fraction (<40%) offers efficient diffusion paths inside a film and a large number of reaction sites for detecting gaseous analytes, enabling fast fluorescence quenching at an early stage (≈7.5 times higher than the solid film at 30 s) and fully suppressed fluorescence without quenching saturation, which cannot be achieved by conventional solid films.

　Although perovskitesolarcells(PSCs)surpassing20%incerti-fied powerconversionefficiency(PCE) have beendemonstrat-ed with organichole-transportinglayers(HTLs), thermaldegra-dationremainsone of the key issuesfor practical applications.We fabricatedPSCs usinglow temperaturesolution-processedCuSCNas the inorganichole-transport layer(HTL),whichpos-sessesahighlystable crystalline structureand is robustevenat hightemperatures.Thebest-performingcell delivers aPCEof 18.0%, with15.9%measured at thestabilizedpoweroutput.Here we reportthe thermalstabilityof PSCsbasedonCuSCNin comparisonwithcommonly used2,2’,7,7’-tetrakis-(N,N-di-4-methoxyphenylamino)-9,9’-spirobifluorene(spiro-OMeTAD).The PSC fabricatedwithorganicspiro-OMeTAD de-gradesto 25%ofinitialPCE afterannealing for 2hat 1258Cinair under40%averagerelativehumidity.However,CuSCN-basedPSCsmaintainapproximately60%ofthe initialvalue,exhibitingsuperiorthermalstabilityunderidenticalconditions.Thisworkdemonstratesthathighefficiencyandimprovedthermalstability are simultaneouslyachievedwhenCuSCNisusedas an HTL in PSCs.

　This work describes controlling charge transport properties of organic field-effect transistors (OFETs) with dicyanodistyrylbenzene-based organic semiconductors. Four fluorinated dicyanodistyrylbenzene derivatives (hTF1, hTF2, hTF3, and hTF5) with different degree of fluorination at the phenyl peripheries were synthesized and subjected to OFET devices. It was shown that the fluorination distinctly alters the polarity of charge transfer characteristics from p-type (hTF1), ambipolar (hTF2, hTF5), to n-type (hTF3). Systematic studies on photophysical, electrochemical, structural, and electronic properties revealed the fine tuning of the charge transport properties by the degree of fluorination. While p-type mobility of hTF1 was smaller than 0.01 cm2V−1 s−1, n-type mobility of hTF3 was as large as 0.7 cm2 V−1 s−1. On the other hand, well-balanced ambipolar mobilities were achieved for both hTF2 and hTF5 (hole and electron mobilities were virtually equal to be 0.07 cm2 V−1 s−1).

　A novel nitronyl-nitroxide derivative for highly sensitive and selective detection of ascorbic acid (AA) is reported. The probe showed 260-fold fluorescence turn-on and diminished electron spin resonance (ESR) signal upon AA addition. The probe could detect AA over a broad concentration range from 1 μM to 2 mM and excellent selectivity over various antioxidants and acids through a combination of fluorescence and ESR responses, which originated from the dual-reactiveness of dual-quenching group nitronyl-nitroxide. We successfully demonstrated practical application potential of the probe by preparing nanoparticles and sensor papers and determining AA concentration in real samples including vitamin drinks and orange juices.

　A long-standing dream in the large scale application of solar energy conversion is the fabrication of solar cells with high-efficiency and long-term stability at low cost. The realization of such practical goals depends on the architecture, process and key materials because solar cells are typically constructed from multilayer heterostructures of light harvesters, with electron and hole transporting layers as a major component. Recently, inorganic–organic hybrid lead halide perovskites have attracted significant attention as light absorbers for the fabrication of low-cost and high-efficiency solar cells via a solution process. This mainly stems from long-range ambipolar charge transport properties, low exciton binding energies, and suitable band gap tuning by managing the chemical composition. In our pioneering work, a new photovoltaic platform for efficient perovskite solar cells (PSCs) was proposed, which yielded a high power conversion efficiency (PCE) of 12%. The platform consisted of a pillared architecture of a three-dimensional nanocomposite of perovskites fully infiltrating mesoporous TiO2, resulting in the formation of continuous phases and perovskite domains overlaid with a polymeric hole conductor. Since then, the PCE of our PSCs has been rapidly increased from 3% to over 20% certified efficiency. The unprecedented increase in the PCE can be attributed to the effective integration of the advantageous attributes of the refined bicontinuous architecture, deposition process, and composition of perovskite materials. Specifically, the bicontinuous architectures used in the high efficiency comprise a layer of perovskite sandwiched between mesoporous metal–oxide layer, which is a very thinner than that of used in conventional dye-sensitized solar cells, and hole-conducting contact materials with a metal back contact. The mesoporous scaffold can affect the hysteresis under different scan direction in measurements of PSCs. The hysteresis also greatly depends on the cell architecture and perovskite composition. In this Account, we will describe what we do with major aspects including (1) the film morphology through the development of intermediate chemistry retarding the rapid reaction between methylammonium or formamidinium iodide and lead halide (PbI2) for improved perovskite film formation; (2) the phase stability and band gap tuning of the perovskite layer through the materials engineering; (3) the development of electron and hole transporting materials for carrier-selective contacting layers; and (4) the adoption of p–i–n and n–i–p architectures depending on the position of the electron or hole conducting layer in front of incident light. Finally, we will summarize the recent incredible achievements in PSCs, and finally provide challenges facing the future development and commercialization of PSCs.