Surface passivation using pyridinium iodide for highly efficient planar perovskite solar cells

Perovskite solar cells have developed rapidly in the past decades.However,there are large amounts of ionic defects at the surface and grain boundaries of perovskte films which are detrimental to both the efficiency and stability of perovskite solar cells.Here,an organic halide salt pyridinium iodide(PyI) is used in cation-anion-mixed perovskite for surface defect passivation.Different from the treatment with Lewis base pyridine(Py) which can only bind to the under-coordinated Pb ions,zwitterion molecule PyI can not only fill negative charged iodine vacancies,but also interact with positive charged defects.Compared with Py treatment,PyI treatment results in smoother surface,less defect densities and nonradiative recombination in perovskite,leading to an improved VOC, negligible J-V hysteresis and stable performance of devices.As a result,the champion PyI-treated planar perovskite solar cell with a high VOC of 1.187 V achieves an efficiency of 21.42%,which is higher than 20.37% of Py-treated device,while the pristine device without any treatment gets an efficiency of 18.83% at the same experiment conditions.

Chromium trioxide modified spiro-OMeTAD for highly efficient and stable planar perovskite solar cells

Hole transporting materials(HTMs)play an unparalleled role in heightening the stability and photovoltaic performance of perovskite solar cells(PSCs).The organic small molecule spiro-OMeTAD is frequently utilized for HTM in PSCs.However,the raw spiro-OMeTAD without dopant would be harmful to the development of highly efficient PSCs,due to its unsatisfied hole mobility and conductivity.Therefore,we introduce an inorganic dopant(chromium trioxide,CrO_(3))into the lithium-salt doped spiro-OMeTAD.Because of the exclamatory oxidizability of CrO_(3),it can accelerate the oxidation of spiro-OMeTAD and thereby enhancing the hole mobility of HTM.The introduction of CrO_(3) not only substantially decreases the density of defects,but also adjusts spiro-OMeTAD energy band,and thus effectively suppresses the hysteresis and improving stability of PSCs.In the end,we obtained a power conversion efficiency(PCE)as high as 22.6%after doping CrO_(3) in spiro-OMeTAD.The facile,low cost and outstanding photovoltaic performance render CrO_(3) an excellent dopant for HTMs in PSCs.

NaHCO_(3)-induced porous PbI_(2) enabling efficient and stable perovskite solar cells

Driven by their many unique features,perovskite solar cells(PSCs)have become one of the most promising candidates in the photovoltaic field.Two-step preparation of perovskite film is advantageous for its higher stability and reproducibility compared to the one-step method,which is more suitable for practical application.However,the incomplete conversion of the dense lead iodide(PbI_(2))layer during the sequential spin-coating of formamidinium/methylammonium(FA^(+)/MA^(+))organic amine salts severely affect the performance of PSCs.Herein,sodium bicarbonate(NaHCO_(3))is used to induce the formation of porous PbI_(2),which facilitates the penetration of the FA^(+)/MA^(+)ions and the formation of a perovskite film with high crystallinity and large grain microstructure.Meanwhile,the introduction of Na^(+)not only improves the energetic alignment of the PSC,but also increases the conductivity via p-doping.As a result,the optimized NaHCO_(3)-modified PSC achieves a champion power conversion efficiency of 24.0% with suppressed hysteresis.Moreover,the significant reduction in defect density and ion migration as well as a mild alkaline environment enhance the stability of device.The unencapsulated NaHCO_(3)-modified PSCs maintain over 90% of their original efficiency upon storage in ambient air(30%–40% relative humidity)for 2160 h.We have demonstrated an ingenious strategy for controlling the quality of perovskite and improving the performance of device by low-temperature foaming of simple inorganic molecules of NaHCO_(3).

Solution processed inorganic V20x as interfacial function materials for inverted planar-heterojunction perovskite solar cells with enhanced efficiency

An inverted planar heterojunction perovskite solar cell （PSC） is one of the most competitive photovoltaic devices exhibiting a high power conversion efficiency （PCE） and nearly free hysteresis in the voltage-current output. However, the band alignment between the transport materials and the perovskite absorber has not been optimized, resulting in a lower open-circuit voltage （Voc） than that of regular PSCs. To address this issue, we tune the band alignment in perovskite photovoltaic architecture by introducing bilayer structured transport materials, e.g., the hole transport material poly（ethylenedioxythiophene）：poly（styrene sulfonate） （PEDOT：PSS）/V2Os. In this study, solution processed inorganic V2Ox interlayer is incorporated into PEDOT：PSS for achieving improved film surface properties as well as optical and electrical properties. For example, the work function （WF） was changed from 5.1 to 5.4 eV. A remarkably high PCE of 17.5% with nearly free hysteresis and a stabilized efficiency of 17.1% have been achieved. Electronic impedance spectra （EIS） demonstrate a significant increase in the recombination resistance after introducing the interlayer, associated with the high Voc output value of 1.05 V. Transient photocurrent and photovoltage measurements indicate that a comparable charge transport process and an inhibited recombination process occur in the PSC with the introduction of the V20x interlayer.

Single-atom sites on perovskite chips for record-high sensitivity and quantification in SERS

Surface enhanced Raman scattering(SERS)is a rapid and nondestructive technique that is capable of detecting and identifying chemical or biological compounds.Sensitive SERS quantification is vital for practical applications,particularly for portable detection of biomolecules such as amino acids and nucleotides.However,few approaches can achieve sensitive and quantitative Raman detection of these most fundamental components in biology.Herein,a noblemetal-free single-atom site on a chip strategy was applied to modify single tungsten atom oxide on a lead halide perovskite,which provides sensitive SERS quantification for various analytes,including rhodamine,tyrosine and cytosine.The single-atom site on a chip can enable quantitative linear SERS responses of rhodamine(10^(−6)-1 mmol L^(−1)),tyrosine(0.06-1 mmol L^(−1))and cytosine(0.2-45 mmol L^(−1)),respectively,which all achieve record-high enhancement factors among plasmonic-free semiconductors.The experimental test and theoretical simulation both reveal that the enhanced mechanism can be ascribed to the controllable single-atom site,which can not only trap photoinduced electrons from the perovskite substrate but also enhance the highly efficient and quantitative charge transfer to analytes.Furthermore,the label-free strategy of single-atom sites on a chip can be applied in a portable Raman platform to obtain a sensitivity similar to that on a benchtop instrument,which can be readily extended to various biomolecules for low-cost,widely demanded and more precise point-of-care testing or in-vitro detection.

Rapid and Complete Conversion of CH3NH3PbI3 for Perovskite/C60 Planar-Heterojunction Solar Cells by Two-Step Deposition

In the present work,we proposed an improved two-step deposition method by optimizing the reaction temperature and the dipping time for the fabrication ofperovskite films.The perovskite film fabricated at 70 ℃ exhibits a full surface coverage and a smooth uniform crystal morphology with a particle size up to micrometer scale.The corresponding inverted perovskite solar cell with a structure of ITO/poly（3,4-ethylenedioxythiophene）：poly（styrene-sulfonate）（PEDOT：PSS）/CH3NH3PbI3/C60/2,9-dimethyl-4,7-diphenyl-l,l 0-phenanthroline （BCP）/Ag displayed a higher power conversion efficiency（PCE）of 13.6%than that of the device fabricated at 20 ℃ （8.06%）,as well as the high reproducibility.The small but meaningful modification for two-step deposition would provide an efficient and convenient way to optimize planar perovskite solar cells and facilitate the potential applications of perovskite solar cells more widely.

OUTPUT-FEEDBACK CONTROL FOR NONHOLONOMIC SYSTEMS WITH LINEAR GROWTH CONDITION

This paper deals with the stabilization of the nonholonomic systems with strongly nonlinear uncertainties. The objective is to design an output feedback law such that the closed-loop system is globally asymptotically regulated at the origin. The systematic strategy combines the input-state scaling technique with the backstepping technique. A novel switching control strategy based on the output measurement of the first subsystem is employed to make the subsystem far away from the origin. The simulation demonstrates the effectiveness of the proposed controller.