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Unusual Bimodal Photovoltaic Performance of Perovskite Solar Cells at Real-World Operating Temperatures
摘要： A deep understanding of environmental effects on perovskite solar cell (PSC) performance is highly desirable for further progress towards large-scale deployment of this technology. We investigate the operation of PSCs in the temperature range (15?50 C) and report an unusual bimodal behavior in photovoltaic (PV) performance, with positive and negative temperature coefficients (TCs) below and above room temperature (RT), respectively. Furthermore, the performance metrics exhibit hysteresis, as their values depend on whether the measurements are made during the heating or cooling stages of the experiment. Conventional semiconductor solar cells, in contrast, exhibit a monotonic and non-hysteretic performance decline in this temperature range. The variations in power conversion efficiency primarily follow changes in open-circuit voltage and fill factor. Photoluminescence data suggest that the performance variations below RT are accompanied by a reduction in defect-related traps in the perovskite absorber and a drop in interfacial built-in potential at the perovskite/transport layer interface. The behavior above RT follows the conventional trend and can hence be explained by charge-phonon interactions. Our findings offer significant insight into the salient PV properties and photophysics of perovskite materials that define their performance in the real-world operating temperature range.
关键词： charge-phonon coupling,temperature-dependent hysteresis,Perovskite solar cells,Temperature coefficient
更新于2025-09-19 17:13:59
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PCE11-based polymer solar cells with high efficiency over 13% achieved by room-temperature processing
摘要： With the emergence and rapid development of new non-fullerene acceptors (NFAs), bulk-heterojunction polymer solar cells (BHJ-PSCs) have achieved high power conversion efficiencies (PCEs) over 16%. Developing effective methods to fabricate high-performance thick-film PSCs is important to meet the requirements of the future roll-to-roll commercial production. PffBT4T-2OD (PCE11) as the most promising temperature-dependent aggregation (TDA) donor with high crystallinity has achieved high performance at high film thickness, which, however, needs at high processing temperature and is detrimental for practical production of large-area PSCs. We designed NFAs, ZITI-N-CH3, ZITI-N-C8H17, and ZITI-N-EH containing different side chains. Because of the excellent miscibility of the TDA-polymer PffBT4T-2OD and ZITI-N-R, the devices can be fabricated at room temperature, achieving a medium PCE of 8.78% for ZITI-N-CH3-based PSC, a high PCE of 12.13% for ZITI-N-C8H17-based PSC and a superior PCE of 13.07% for ZITI-N-EH-based PSC, which is attributed to the smallest domain size and highest crystallization for PffBT4T-2OD:ZITI-N-EH blend. The PCE of 13.07% is the highest among the TDA polymer-based PSCs, which can be maintained at 12.35% at the high thickness of 200 nm. This work provides an important guideline to develop high-performance thick-film TDA-polymer-based non-fullerene PSCs at mild processing conditions.
关键词： temperature-dependent aggregation,room-temperature processing,polymer solar cells,high efficiency,non-fullerene acceptors
更新于2025-09-19 17:13:59
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[IEEE 2019 1st International Conference on Advances in Science, Engineering and Robotics Technology (ICASERT) - Dhaka, Bangladesh (2019.5.3-2019.5.5)] 2019 1st International Conference on Advances in Science, Engineering and Robotics Technology (ICASERT) - Design of a Cost Effective Smart Autonomous Power and Switch Controlled Led Street Light
摘要： This paper implies and demonstrates a unique Smart Autonomous power and switch controlled Led Street Lighting System for Bangladesh. As we live in the age of globalization where streetlights are very much important for a city infrastructure in the crowded regions, the autonomous power and switching of these streetlights can have a huge impact in our electricity usage and minimize the wastage of electricity. Usually street light is needed at the time of sunset until the sunrise, but during peak hours (time 17:00 pm to 20:00 pm), the electricity demand is higher than electricity supply from the National Grid for many under developing countries including Bangladesh as this is the high time of excessive usage of Home Loads like Television, Air-Cooler etc. Proposed herein is a design and practically implementation of a smart autonomous power and switch controlled street light system by using stored solar energy during peak hours and light dependent resistor based energy efficient automatic Streetlight switching rather than the conventional switching operations. Besides temperature sensor and Real time clock (RTC) are being attached to display the updated time and temperature to the nearby passengers of the vehicles and walkers of the street sides. Thus, proper implementation of the proposed system will be able to be a medium for an energy efficient circuit, national grid’s power scarcity minimizer and free cost of energy and high reliability.
关键词： LED Street light,Real Time Clock,Relay operation,Light Dependent Resistor (LDR),Temperature sensor,ARDUINO UNO
更新于2025-09-16 10:30:52
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[IEEE 2019 18th International Conference on Optical Communications and Networks (ICOCN) - Huangshan, China (2019.8.5-2019.8.8)] 2019 18th International Conference on Optical Communications and Networks (ICOCN) - Low Polarization Dependent Loss Two-Dimensional Grating Coupler
摘要： We design and demonstrate a two-dimensional grating coupler (2D GC) with a low polarization dependent loss (PDL) based on the silicon-on-insulator (SOI) platform. Using an elliptical-like etching pattern consisting of two identical semicircles and a rectangle embedded between them, a maximum PDL of the fabricated device is measured to be 0.2 dB covering the C-band, lower than that of most conventional 2D GCs. Besides, a large feature size of 280 nm is beneficial to its manufacturing process and wide application.
关键词： grating coupler,large feature size,low polarization dependent loss
更新于2025-09-16 10:30:52
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From normal diffusion to superdiffusion: Photothermal heating of plasmonic core-shell microgels
摘要： The motion of core-shell colloids during laser heating is studied using angle-dependent pump-probe dynamic light scattering. The cores consist of a single spherical gold nanoparticle whose localized surface plasmon resonance has a strong spectral overlap with the wavelength of the pump laser. They are homogeneously encapsulated in thick hydrogel shells composed of either chemically cross-linked poly-N-isopropylacrylamide or poly[2-(2-methoxyethoxy)ethyl methacrylate], both of which exhibit a temperature-dependent volume phase transition. Thus, upon heating beyond the transition temperature, the hydrogel shells shrink. Intensity-time autocorrelation functions are recorded while illuminating the samples with the pump laser and hence heating the gold cores. With increasing laser intensity, the dynamics changes from normal Brownian motion to superdiffusion. Nevertheless, in the high-q limit, the relaxation times can be extracted and used to estimate the temperature increase, which can reach almost 10 K. This causes a significant deswelling of the hydrogel shells, which is also measured.
关键词： temperature-dependent volume phase transition,photothermal heating,dynamic light scattering,superdiffusion,plasmonic core-shell microgels
更新于2025-09-16 10:30:52
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Slow and Stopped Light in a Time-Dependent Moiré Grating
摘要： The reduction in the group velocity of a light pulse due to a resonance is termed slow light. A velocity reduction to 17 m/s was demonstrated using electromagnetically induced transparency (EIT) [1]. It was later demonstrated that light could be stopped completely [2-3]. Whilst slow light EIT experiments have been ground breaking, they require a vapour cloud cooled close to 0 K. Here we present a possible alternative using gratings and a time-dependent refractive index. Slow light can be induced by a Bragg grating by propagating a pulse with a carrier frequency close to the rejection band created by the Bragg resonance. This is accompanied by a substantial increase in group velocity dispersion (GVD) causing significant pulse broadening and limiting practical uses. A Moiré grating, which is a superposition of two grating periods has been suggested as a potential solution to reduce GVD [4]. The two grating periods produce two rejection bands separated by a transmission band. Propagating a pulse through the transmission band induces slow light, but the GVD generated by one rejection band is compensated by the other. We have developed a parametrisation for the Moiré grating periods such that they produce a transmission band centred on a given carrier frequency. Further using the parametrisation, we have derived a set of modified coupled mode equations, describing the coupling of the amplitudes A and B of the forward and backward propagating light for gratings of strength (cid:78) and with (cid:47)s the Moiré period and (cid:39)b the detuning. Our numerical simulations of a frequency-resolved version of Eq. (1) confirm that Moiré gratings produce slow light with minimal pulse broadening. The bandwidth of the rejection bands is dependent on the strength of the grating which is controlled by the grating modulation ?n. As the grating strength is increased, the rejection bands broaden reducing the transmission gap. If the grating strength is increased sufficiently the transmission band will close. Figures 1(a) and (b) show simulations of pulse propagation through a Moiré grating using finite difference time domain (FDTD) methods. The group velocity is given by the gradient of propagation distance versus time. Figure 1(a) shows propagation for a time-independent ?n. In Figure 1(b), ?n is increased by a time-dependent refractive index [5]; at 190 ps ?n is increased so that the transmission gap closes and is decreased to its original value at 440 ps, reopening the transmission gap. Closing the transmission band whilst a pulse is propagating through the grating induces stopped light. The pulse becomes trapped and remains stationary within the grating until the grating strength is reduced and the pulse can continue to propagate, analogous to results achieved in EIT [2-3]. Figure 1(c) shows how the transmission band closes as a function of the grating modulation. While the realisation of a time-dependent Moiré grating remains challenging, it presents a versatile alternative to the storage and release of light pulses in a solid-state platform, which would provide an essential element for, e.g., quantum information processing.
关键词： time-dependent refractive index,stopped light,slow light,group velocity dispersion,Moiré grating
更新于2025-09-16 10:30:52
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Substituted stilbene-based oxime esters used as highly reactive wavelength-dependent photoinitiators for LED photopolymerization
摘要： Six novel oxime carboxylate photoinitiators were designed on the basis of a π-conjugated (E)-1-(4-styryl-phenyl)-1-one subunit. Different substituent groups were introduced into three distinctive sites of the chromophore to rationalize their related electronic and structural effects on free-radical photoinitiating reactivities. The electronic properties, photodissociation mechanism, and structure–reactivity relationships were investigated by UV–visible spectroscopy, DFT calculations, real-time 1H NMR, electron spin resonance spectroscopy, and photo-DSC. We demonstrate that the structural change affecting the photoinitiating properties corresponds to a para-substitution effect on the stilbene subunit using an electron-acceptor group. Such a structural change leads to a 10-fold enhancement in initiation efficiency (Φi) upon visible irradiation of light-emitting diodes. The photoinitiating performances of these new derivatives are strikingly sensitive to the excitation wavelengths, leading to an impressive enhancement of Φi by more than three orders of magnitude from 365 nm to 405 nm irradiation. This wavelength-dependent reactivity previously observed for commercially available oxime esters can be generalized in our series and has high potential photocuring applications in low-power visible LEDs.
关键词： photocuring,photoinitiators,LED photopolymerization,oxime esters,wavelength-dependent
更新于2025-09-16 10:30:52
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[IEEE 2019 18th International Conference on Optical Communications and Networks (ICOCN) - Huangshan, China (2019.8.5-2019.8.8)] 2019 18th International Conference on Optical Communications and Networks (ICOCN) - Exciton tunneling behaviors in two dimensional halide perovskite
摘要： Two-dimensional (2D) halide perovskite materials have attracted great attention because of their impressive optoelectronic properties in light-emitting diodes (LED), sensors and solar cells, etc. Recently, it has been shown that the low dimensional perovskites with direct white light emission may act as the single component phosphors in next generation white-LEDs. Here, we demonstrate temperature dependent photoluminescence (PL) properties of white light 2D perovskites. Spectroscopic measurements suggest that the white light spectrum consist of free exciton (FE) and self-trapped exciton (STE). The relative intensities between the FE and STE are temperature dependent, and the energy tunneling effect is dominated at low temperature while the thermal quenching is responsible for the higher temperature region. Our results give the physical insight of the energy transfer and thermal behaviours of the excitons in 2D perovskites.
关键词： Temperature dependent PL,Excitons,2D materials
更新于2025-09-16 10:30:52
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Dynamic growth of rhombic dodecahedral Cu <sub/>2</sub> O crystals controlled by reaction temperature and their size-dependent photocatalytic performance
摘要： Compared with low-index {100} or {111} planes of Cu2O crystals, rhombic dodecahedra (RD) Cu2O crystals exposing 12 {110} facets exhibit the most superior photodegradation of organic pollutants. Herein, a series of RD Cu2O crystals with different sizes were successfully synthesized by precisely adjusting the reaction temperature ranging from 40 °C to 100 °C. The results revealed that truncated rhombic dodecahedra (TRD) Cu2O crystals were fabricated when the temperatures was 40 °C. More importantly, on raising the temperature to above 40 °C, Cu2O architectures dynamically evolved from TRD to RD. Meanwhile, the sizes gradually decreased with elevation of the temperature, while the RD morphology of Cu2O crystals remained, demonstrating the importance of temperature for determining the morphology and size of Cu2O crystals. In addition, we also carefully investigated the visible-light photodegradation performance of Cu2O crystals for methyl orange (MO). RD Cu2O crystals exhibited superior photocatalytic activity compared with TRD, and showed size-dependent photocatalytic activity for MO. The photocatalytic activity of RD Cu2O crystals can be greatly improved by decreasing the size. In particular, RD-60 with the minimum size achieved the best photocatalytic properties compared to the other RD and TRD Cu2O crystals, and still displayed high photocatalytic efficiency even after three cycles. Such results advance the understanding that temperature modulation serves as an effective means to fabricate RD Cu2O crystals.
关键词： size-dependent photocatalytic performance,photodegradation,reaction temperature,Cu2O crystals,rhombic dodecahedra
更新于2025-09-16 10:30:52
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[IEEE TENCON 2019 - 2019 IEEE Region 10 Conference (TENCON) - Kochi, India (2019.10.17-2019.10.20)] TENCON 2019 - 2019 IEEE Region 10 Conference (TENCON) - An Alternative Approach to Voltage Dependent Reduction of Schottky Barrier Height Modeling in Two Dimensional MSM Photodetectors
摘要： Current-voltage (I-V) characteristics of a two dimensional MSM photodetector can be explained by modified thermionic emission diffusion (TED) theory. The theory assumes that Schottky barrier height (SBH) decreases linearly with bias voltage and hence voltage dependent reduction of SBH is understood in term of a series resistance (Rs) and ideality factor (n). Characterization of Rs and n can be done from dV d(lnI) vs I plot. However, in this paper we are presenting an alternative approach to understanding characteristics of voltage dependent reduction of SBH. We are proposing an exponential relationship between reduction of SBH and bias voltage to understand non ideality of Schottky junctions. By applying this relationship directly into the Richardson-Dushman equation photocurrents of different Transition-Metal Dichalcogenides(TMD) based devices can be estimated analytically. This model offers a simplistic approach for understanding non ideal behaviour of Schottky barrier height. Using this model we have calculated I-V characteristics of four different TMD based photodetectors under illumination as reported in literature. We have observed good agreement of our calculated results with experimental values. Mean absolute error in each of the cases was found to be not more than 6% in these calculations.
关键词： Perovskite,Voltage Dependent Schottky Barrier Height,Transition-Metal Dichalcogenide,Photodetector
更新于2025-09-16 10:30:52