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The visual and instantaneous detection of trace levels of toxic lead ions (Pb2+) in water is still challenging. In this study, a perovskite precursor-based fluorescent sensor for visual and instantaneous...

Perovskite-based photovoltaic materials have been attracting attention for their strikingly improved performance at converting sunlight into electricity. The beneficial and unique optoelectronic characteristics of perovskite structures enable researchers to achieve an incredibly remarkable power conversion efficiency. Flexible hybrid perovskite photovoltaics promise emerging applications in a myriad of optoelectronic and wearable/portable device applications owing to their inherent intriguing physicochemical and photophysical properties which enabled researchers to take forward advanced research in this growing field. Flexible perovskite photovoltaics have attracted significant attention owing to their fascinating material properties with combined merits of high efficiency, light-weight, flexibility, semi-transparency, compatibility towards roll-to-roll printing, and large-area mass-scale production. Flexible perovskite-based solar cells comprise of 4 key components that include a flexible substrate, semi-transparent bottom contact electrode, perovskite (light absorber layer) and charge transport (electron/hole) layers and top (usually metal) electrode. Among these components, interfacial layers and contact electrodes play a pivotal role in influencing the overall photovoltaic performance. In this comprehensive review article, we focus on the current developments and latest progress achieved in perovskite photovoltaics concerning the charge selective transport layers/electrodes toward the fabrication of highly stable, efficient flexible devices. As a concluding remark, we briefly summarize the highlights of the review article and make recommendations for future outlook and investigation with perspectives on the perovskite-based optoelectronic functional devices that can be potentially utilized in smart wearable and portable devices.

Lead (Pb)–Tin (Sn) mixed perovskites suffer from large open-circuit voltage (Voc) loss due to the rapid crystallization of perovskite films, creating Sn and Pb vacancies. Such vacancies act as defe...

Precise control over the charge carrier dynamics throughout the device can result in outstanding performance of perovskite solar cells (PSCs). Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is the most actively studied hole transport material in p-i-n structured PSCs. However, charge transport in the PEDOT:PSS is limited and inefficient because of its low conductivity with the presence of the weak ionic conductor PSS. In addition, morphology of the underlying PEDOT:PSS layer in PSCs plays a crucial role in determining the optoelectronic quality of the active perovskite absorber layer. This work is focused on realization of a non-wetting conductive surface of hole transport layer suitable for the growth of larger perovskite crystalline domains. This is accomplished by employing a facile solvent-engineered (ethylene glycol and methanol) approach resulting in removal of the predominant PSS in PEDOT:PSS. The consequence of acquiring larger perovskite crystalline domains was observed in the charge carrier dynamics studies, with the achievement of higher charge carrier lifetime, lower charge transport time and lower transfer impedance in the solvent-engineered PEDOT:PSS-based PSCs. Use of this solvent-engineered treatment for the fabrication of MAPbI3 PSCs greatly increased the device stability witnessing a power conversion efficiency of 18.18%, which corresponds to ∼37% improvement compared to the untreated PEDOT:PSS based devices.

In this work, grain boundary (GB) potential barrier ( Δφ GB), dopant density (Pnet), and filled trap state density (PGB,trap) were manipulated at the nanoscale by exposing the fabricated perovskite films to various relative humidity (RH) environments. Spatial mapping of surface potential in the perovskite film revealed higher positive potential at GBs than inside the grains. The average Δφ GB, Pnet, and PGB,trap in the perovskite films decreased from 0% RH to 25% RH exposure, but increased when the RH increased to 35% RH and 45% RH. This clearly indicated that perovskite solar cells fabricated at 25% RH led to the lowest average GB potential, smallest dopant density, and least filled trap states density. This is consistent with the highest photovoltaic efficiency of 18.16% at 25% RH among the different relative humidities from 0% to 45% RH.

Achieving long-term stability along with high power conversion efficiency (PCE) is the biggest obstacle for the pursuit of organic–inorganic perovskite solar cells (PSCs) toward commercialization. ...

Lithium metal anodes have attracted extensive attention owing to their high theoretical specific capacity. However, the notorious reactivity of lithium prevents their practical applications, as evidenced by the undesired lithium dendrite growth and unstable solid electrolyte interphase formation. Here, we develop a facile, cost-effective and one-step approach to create an artificial lithium metal/electrolyte interphase by treating the lithium anode with a tin-containing electrolyte. As a result, an artificial solid electrolyte interphase composed of lithium fluoride, tin, and the tin-lithium alloy is formed, which not only ensures fast lithium-ion diffusion and suppresses lithium dendrite growth but also brings a synergistic effect of storing lithium via a reversible tin-lithium alloy formation and enabling lithium plating underneath it. With such an artificial solid electrolyte interphase, lithium symmetrical cells show outstanding plating/stripping cycles, and the full cell exhibits remarkably better cycling stability and capacity retention as well as capacity utilization at high rates compared to bare lithium., Here the authors report a simple method to create a solid electrolyte interphase that is tightly anchored onto the surface of lithium metal anode. This artificial structure suppresses dead and dendrite Li and stores Li via formation of alloys, enabling impressive battery performance.

In this work, methylammonium lead triiodide (CH3NH3PbI3) perovskite solar cells with efficiencies higher than 18% were achieved using a new nanocomposite hole transport layer (HTL) by doping poly(ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) with a mixed dopant of polyaniline (PANI) and graphene oxide (GO). A synergistic engineering between GO, PANI, and PEDOT:PSS was accomplished to introduce additional energy levels between perovskite and PEDOT:PSS and increase the conductivity of PEDOT:PSS. Kelvin probe force microscope results confirmed that adding GO to PEDOT:PSS/PANI composite significantly reduced the average surface potential. This increased the open circuit voltage (Voc) to 1.05 V for the GO/PEDOT:PSS/PANI nanocomposite perovskite solar cells from the pristine PEDOT:PSS (Voc = 0.95 V) and PEDOT:PSS/PANI (Voc = 0.99 V). In addition, adding PANI to the HTLs substantially enhanced short circuit current density (Jsc). This was supported by the current sensing‐atomic force microscopy (CS‐AFM) and conductivity measurements. The PANI doped films showed superior electrical conductivity compared with those without PANI as indicated by CS‐AFM results. PANI can fill the gaps between the microflakes of GO and give rise to more compact hole transport material (HTM) layer. This led to a higher Jsc after doping with PANI, which was consistent with the incident photon‐to‐current efficiency and electrochemical impedance spectroscopy results. The results of X‐ray diffraction (XRD) and AFM indicated the GO/PANI doped HTMs significantly improved the crystallinity, topography, and crystal size of the perovskite film grown on their surface. A higher efficiency of 18.12% for p‐i‐n perovskite solar cells has been obtained by adding the mixed dopant of GO, PANI, and PEDOT:PSS, demonstrating better stability than the pristine PEDOT:PSS cell.

We demonstrate a highly sensitive and selective sensing platform for the electrochemical detection of Hg2+ in aqueous media. A graphene oxide (GO) and silver nanowire (AgNW) nanocomposites modified...

Perovskites have been unprecedented with a relatively sharp rise in power conversion efficiency in the last decade. However, the polycrystalline nature of the perovskite film makes it susceptible to surface and grain boundary defects, which significantly impedes its potential performance. Passivation of these defects has been an effective approach to further improve the photovoltaic performance of the perovskite solar cells. Here, we report the use of a novel hydrazine-based aromatic iodide salt or phenyl hydrazinium iodide (PHI) for secondary post treatment to passivate surface and grain boundary defects in triple cation mixed halide perovskite films. In particular, the PHI post treatment reduced current at the grain boundaries, facilitated an electron barrier, and reduced trap state density, indicating suppression of leakage pathways and charge recombination, thus passivating the grain boundaries. As a result, a significant enhancement in power conversion efficiency to 20.6% was obtained for the PHI-treated perovskite device in comparison to a control device with 17.4%.

Herein, we clearly demonstrate that the inclusion of the organic solid additive (2,3-dihydroxypyridine, DOH) into the poly(diketopyrrolopyrrole-terthiophene) (PDPP3T) and phenyl-C61-butyric acid methyl ester (PCBM) (PDPP3T:PCBM) photoactive blend system alters the nanoscale morphology and enhances the photovoltaic (PV) performance of the inverted bulk heterojunction (BHJ) based polymer solar cells (PSCs). The influence of DOH additive casted PDPP3T: PCBM thin films on the optical, morphology and structural features is evaluated and correlated with PV characteristics. Topography images through atomic force microscopy reveal that the incorporation of DOH into PDPP3T: PCBM induces a finer nanoscale phase segregation between polymer and fullerene domains with fibrillar morphology. The PV performance of the DOH processed PDPP3T: PCBM devices is evaluated by current-voltage (J-V) characteristics and compared with pristine and 1, 8-diiodooctane (DIO) modified PDPP3T: PCBM devices. Interestingly, the incorporation of DOH (0.5 wt%) into PDPP3T: PCBM device witnessed the best PCE of 6.36%, which is significantly higher (69.1%) than that of the reference (3.76%). This significant enhancement in the performance of the device is mainly attributed to a dramatic increase in the short-circuit current density and fill-factor due to the improved bicontinuous interpenetrated phase separation and balanced charge transport. In addition, the measurements on photo-induced charge carrier extraction by linearly increasing voltage reveal that DOH incorporated devices exhibit higher mobility and charge carrier density as compared to those of pristine modified BHJ PSCs. The presence of vicinal functional groups in DOH contributes to the possible molecular level interactions with the blend components and accounts for the morphology and device performance enhancements.

In this work, oxygen vacancies were created to activate tungsten trioxide (WO3) as a highly efficient counter electrode (CE) in dye-sensitized solar cells (DSSCs). The levels of oxygen vacancies (OVs) in WO3 were finely formed and tuned by doping with different weight percentages (3, 5, and 9 wt%) of urea and annealing in a N2 environment at 470 °C. The urea doped WO3 significantly improved the electrocatalytic behaviour in the iodide–triiodide electrolyte. The effects of OVs on the catalytic performance of WO3 CEs were fully studied and understood. This improvement was attributed to the introduction of OVs into WO3, which acted as surface shallow states to facilitate electron transfer from the WO3 counter electrode to the electrolyte. At a high temperature of 470 °C, urea decomposes into the reactive H2 gas that can remove oxygen atoms from the WO3 surface and create OVs. 5 wt% urea was found to be the optimal urea concentration that led to the highest catalytic performance as evidenced by the cyclic voltammetry measurements. The 5 wt% urea doped WO3 CE-based device achieved a power conversion efficiency (PCE) of ∼10.5%, which was improved from the reference Pt CE-based device at ∼9.3% and non-active WO3 CE based cell at 3.32%. This has led to the optimal number of OVs that facilitate the charge transfer at the CE/electrolyte interface.

Sodium-ion batteries (SIBs) are considered as a promising alternative to lithium-ion batteries in large-scale energy storage due to the abundant sodium resources and low cost. However, the practical applications are still hindered by several factors such as limited cycling life and low mass loading of the electrode. Herein, a uniform free-standing Sn-based (Sn@CFC) electrode was synthesized via a facile electrospinning method. The cross-link nitrogen-doped carbon fiber and ultrasmall metallic Sn nanoparticles together provide fast ions and electrons pathway, enabling a dominant pseudocapacitance contribution of 87.1% at a scan rate of 0.5 mV s−1. The Sn@CFC electrode hence exhibits a high reversible area capacity of 1.68 mAh cm−2 at 50 mA g−1 and long cycle life of 1000 cycles at 200 mA g−1 with more than 80% capacity retention. Moreover, the facile manufacturing technique yields the Sn@CFC electrode with an extremely high mass loading of 5.5 mg cm−2 with very little sacrifice of electrochemical performances. This study provides a promising route to scalably fabricate electrodes with high area capacity and high energy density for advanced SIBs.

In this article, photovoltaic performance of dye-sensitized solar cells (DSSCs) has been improved by integrating one-dimensional (1-D) plasmonic Ag nanowires into the mesoporous TiO 2 photoanode. We fabricate series of DSSCs by varying the concentrations of Ag nanowires ranging from 0.0 to 1.2 wt.% to evaluate the performance of DSSCs. The localized surface plasmon resonance (LSPR) of Ag nanowires is utilized to enhance light absorption of dye molecules in the mesoporous TiO 2 photoanode. We found that a 0.9 wt.% of Ag nanowires in the TiO 2 photoanode gave an optimum DSSC performance with an enhancement of short circuit current density and power conversion efficiency from 17.14 to 20.30 mA/cm 2 , and 7.57–9.41% respectively as compared to DSSC without Ag nanowires. The enhancement in photovoltaic performance was ascribed to the improvement in light harvesting by LSPR from Ag nanowires.

Organic-inorganic perovskite cell has shown a great deal of interest in past few years due to its ability to achieve high power conversion efficiency (PCE). Use of charge transport layers such as n-type TiO2 and p-type doped spiroOMeTAD in a n-i-p device architecture has shown enhanced perovskite solar cell device performance. Use of doped spiroOMeTAD as hole transport layer in the n-i-p device structure has been effective but possess disadvantages such as complex processing, use of corrosive additives, processing in ambient air for efficient hole doping. Here we report the study of solution processed benzodithiophene based polymer PBDTT-FTTE as an alternative hole transport layer to doped small molecule spiroOMeTAD. PBDT-FTTE doped with 3% DIO (diiodooctane) achieved PCE of 11.6% which was comparable to matching PCE of 11.6% obtained from using spiroOMeTAD as hole transport layer. We showed that unlike spiroOMeTAD, polymer PBDTT-FTTE is processed inside N2 filled glove box and is easier to process as compared to spiroOMeTAD which requires processing in ambient humid air and is doped with additives mixed in corrosive solvent, causing degradation to perovskite layer underneath.

The efficiencies of perovskite solar cells have been significantly increased to 18%, 17.01% and 15.6% for the cells containing the additives BMImI, LiI and LiTFSI in the PbI2 precursor solutions, respectively, from 11.3% for the devices without any additives. Incorporation of these additives led to the formation of perovskites with larger grain size and higher crystallinity with reduced PbI2 residue as indicated by X-ray diffraction (XRD) and atomic force microscopy (AFM) results. Kelvin Probe Force Microscopy (KPFM) and current sensing (CS)-AFM results were in good agreement with external quantum efficiency (EQE) measurements and proved the great enhancement in short circuit current density (Jsc) as a result of doping. Transient photovoltage measurement results exhibited longer charge carrier lifetimes for the additive incorporated perovskites than those without additives, thus improving the fill factor (FF) and open circuit voltage (Voc). In addition to the improved efficiency, the incorporation of these additives led to higher stability of the CH3NH3PbI3 perovskite solar cells. The new additive BMImI, LiI and LiTFSI incorporated CH3NH3PbI3 perovskite solar cells exhibited a reduced degradation with a 57%, 60%, and 91% decrease in performance respectively after exposure to air for 70 days compared to a 93% decrease for the pristine cell after only 24 days. The lithium salt additives can serve as desiccants to absorb moisture preventing perovskite degradation. Further, the BMImI additive can prevent the formation of free radicals in perovskites upon exposure to light and heat.

A compatible low-bandgap donor polymer (poly[N-90-heptadecanyl-2,7carbazole-alt-3,6-bis(thiophen-5-yl)-2,5-dioctyl-2,5-dihydropyrrolo[3,4]pyrrole-1,4-dione], PCBTDPP) was judicially introduced into the archetypal poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PC61BM) photoactive system to fabricate highly efficient ternary based bulk heterojunction polymer solar cells (PSCs). The PCBTDPP ternary-based PSC with optimal loading (0.2 wt.%) displayed outstanding performance with a champion power conversion efficiency (PCE) of 5.28% as compared to the PCE (4.67%) for P3HT:PC61BM-based PSC (reference). The improved PCE for PCBTDPP ternary-based PSC can be mainly attributed to the incorporation of PCBTDPP into P3HT:PC61BM that beneficially improved the optical, morphological, electronic, and photovoltaic (PV) performance. This work instills a rational strategy for identifying components (donor/acceptor (D/A) molecules) with complementary beneficial properties toward fabricating efficient ternary PSCs.

Organic-inorganic perovskite solar cells have attracted great attention because of low processing cost and high photovoltaic performance over the last few years. This work shows the effect of the density of deep defect states at the mesoporous TiO 2 interface on the photovoltaic characteristics of perovskite solar cell. Charge transport for perovskite solar cells is modeled based on the physics of charge emission, charge capture, and recombination processes assisted by deep interfacial trap states at perovskite / mesoporous TiO 2 interface. This model suggests that back recombination process of holes and electrons at the perovskite / mesoporous TiO 2 interface occurs due to trapping of conduction band electrons and valence band holes by deep trap states. The developed model further studied the impact of interface states on the photovoltaic performance of perovskite solar cells.

Perovskite solar cells (PSCs) have received considerable attention in recent years due to their low processing cost and high‐power conversion efficiency. However, the mechanisms of PSCs are not fully understood. A model based on a probabilistic and statistical approach needs to be developed to simulate, optimize, and predict the photovoltaic (PV) performance of PSC. Herein, the 3D model based on the kinetic Monte Carlo (KMC) approach is developed to simulate 3D morphology of perovskite‐based solar cells and predict their PV performances and charge dynamics. The developed 3D model incorporates the temporal and physical behavior of perovskites, such as charge generation, transport, and recombination. The KMC simulation results show that pin holes‐free perovskite films with a homogenous 400 nm thick perovskite capping layer achieve the highest power conversion efficiency of 20.85%. However, the shortest apparent charge transport time (τt) and the longest apparent charge carrier recombination lifetime (τr) are found for the champion device. PV performance from the fabricated device is used to validate this simulation model. This model can provide a significant conceptual advance in identifying bottlenecks and guiding novel device designs to further improve the performance of perovskite PVs.

For the first time, room temperature heating free growth and crystallization of perovskite films in ambient air without the use of thermal annealing is reported. Highly efficient perovskite nanorod-based solar cells were made using ITO/PEDOT:PSS/CH3NH3PbI3 nanorods/PC60BM/rhodamine/Ag. All the layers except PEDOT:PSS were processed at room temperature thereby eliminating the need for thermal treatment. Perovskite films were spin coated inside a N2 filled glovebox and immediately were taken outside in air having 40% relative humidity (RH). Exposure to humid air was observed to promote the crystallization process in perovskite films even at room temperature. Perovskite films kept for 5 hours in ambient air showed nanorod-like morphology having high crystallinity, with devices exhibiting the highest PCE of 16.83%, which is much higher than the PCE of 11.94% for traditional thermally annealed perovskite film based devices. It was concluded that moisture plays an important role in room temperature crystallization of pure perovskite nanorods, showing improved optical and charge transport properties, which resulted in high performance solar cells.

We have significantly improved the performance of dye-sensitized solar cells (DSSCs) by incorporating plasmonic Au nanostars into the TiO2 photoanode. Gold nanostars were synthesized and used as localized surface plasmons (LSPs) to enhance the light absorption of DSSCs. The Au nanostars exhibit near infrared (NIR) light absorption at ∼785 nm. The N719 and N749 dye based DSSC devices were fabricated with and without the incorporation of Au nanostars. The power conversion efficiency (PCE) of DSSCs using Au nanostars was increased by ∼20% from 7.1% to 8.4% for N719 cells and by ∼30% from 3.9% to 5.0% for N749 devices. The incident photon-to-current conversion efficiency (IPCE) was improved and the spectral response was broadened over the wavelength range of 380–1000 nm. Electrochemical impedance spectroscopy (EIS) showed that by incorporating Au nanostars, the charge recombination resistance Rct value decreased under both open-circuit and illumination conditions, which indicated high electron density generated in the device photoanode.

Traditional chemical, physical and biological processes for treating wastewater containing textile dye have such disadvantages as high cost, high energy requirement and generation of secondary pollution during treatment process. The advanced oxidation processes technology has been attracting growing attention for the decomposition of organic dyes. Such processes are based on the light-enhanced generation of highly reactive hydroxyl radicals, which oxidize the organic matter in solution and convert it completely into water, CO2 and inorganic compounds. In this presentation, the photocatalytic degradation of dyes in aqueous solution using TiO2 as photocatalyst under solar and UV irradiation has been reviewed. It is observed that the degradation of dyes depends on several parameters such as pH, catalyst concentration, substrate concentration and the presence of oxidants. Reaction temperature and the intensity of light also affect the degradation of dyes. Particle size, BET-surface area and different mineral forms of TiO2 also have influence on the degradation rate.

Charge carrier dynamics and behaviors are key parameters and need to be mapped at the nanoscale in order to search for correct materials for high-performance solar cells. Unfortunately, currently, there are no existing tools or capabilities that can simultaneously map charge carrier dynamics at nanometer range in solar cells. Here we use a Transient Photo-response AFM (TP-AFM) to map for the first time apparent carrier recombination lifetime (τr), transport time (τt) and diffusion length (LD) in hybrid perovskites solar cells. These spatially resolved parameters reveal substantial variations at grain boundaries (GBs) of perovskites. Improved τr, τt and LD at GBs broaden the performance of these state-of-the-art mixed cation perovskites. Detail analysis of these parameters allow us to conclude that reduced density of trap states and recombination in mixed cation perovskites at GBs and its surrounding locations (extending to several nanometers into the grain interior) implies less ion migration. This first of its kind experimental realization of nanoscale mapping of charge carrier dynamics in photovoltaic materials can be used for applications in other optoelectronic devices.

In recent years, hybrid perovskite solar cells (HPSCs) have received considerable research attention due to their impressive photovoltaic performance and low‐temperature solution processing capability. However, there remain challenges related to defect passivation and enhancing the charge carrier dynamics of the perovskites, to further increase the power conversion efficiency of HPSCs. In this work, the use of a novel material, phenylhydrazinium iodide (PHAI), as an additive in MAPbI3 perovskite for defect minimization and enhancement of the charge carrier dynamics of inverted HPSCs is reported. Incorporation of the PHAI in perovskite precursor solution facilitates controlled crystallization, higher carrier lifetime, as well as less recombination. In addition, PHAI additive treated HPSCs exhibit lower density of filled trap states (1010 cm−2) in perovskite grain boundaries, higher charge carrier mobility (≈11 × 10−4 cm2 V−1 s), and enhanced power conversion efficiency (≈18%) that corresponds to a ≈20% improvement in comparison to the pristine devices.

We conducted 2 experiments to determine lysine bioavailability from 2 lipid-coated lysine products. In an in vitro experiment we mixed each lipid-coated lysine product with either alfalfa- or corn-silage at different amounts of acidity. Scanning electron micrographs indicated that surface structure of each lipid-coated lysine particle was eroded after mixing with silage. Additionally, visual evaluation of scanning electron micrographs suggested that peripheral surface abrasion of lipid-coated lysine may be greater when lipid-coated lysine was mixed with alfalfa silage in comparison to corn silage. In a corresponding experiment, in vivo measures of lysine bioavailability to sheep from 2 lipid-coated lysine products and lysine-HCl were determined after mixing in corn silage. Plasma lysine concentrations increased linearly (P < 0.01) in response to abomasal lysine infusion indicating that our model was sensitive to increases in metabolizable lysine flow. Bioavailability of each lipid-coated lysine source and dietary lysine-HCl were calculated to be 23, 15, and 18%, respectively. Even though each dietary source of lysine increased plasma lysine, rates of increases in plasma lysine from one lipid-coated lysine source (linear; P = 0.20) and lysine-HCl (linear; P = 0.11) were not different from plasma lysine levels supported by diet alone. However, the rate of plasma lysine increase in response to lysine from the other lipid-coated lysine source was greater (P = 0.04) than plasma lysine from feed alone. Nonetheless, the rate of plasma lysine increase in response to lipid-coated lysine did not differ (P ≥ 0.70) from the rate of plasma lysine increase from lysine-HCl. Clearly, methods of manufacture, together with physical and chemical characteristics of diet, can impact amounts of metabolizable lysine provided from lipid-coated lysine products. Direct measures of lysine bioavailability from lipid-coated lysine products after mixing with diets should be based on measurements with the products treated similarly to the method of feeding.

Smooth, compact and defect free morphology of perovskite is highly desired for enhanced device performance. Several routes such as thermal annealing, use of solvent mixtures, growth under controlled humidity has been adopted to obtain crystalline, smooth and defect free perovskite film. Herein we showed direct use of water (H2O) as co-solvent in precursor solution and have optimized the water content required to obtain smooth and dense film. Varying concentration of water was used in precursor solution of CH3NH3I and PbI2 mixed in γ-butyrolactone (GBL) and dimethylsulfoxide (DMSO). Perovskite films were crystallized using toluene assisted solvent engineering method using GBL:DMSO:H2O as solvent mixture. The amount of water was varied from 1% to 25%, which resulted in change in film morphology and perovskite crystallinity. It was concluded that an appropriate amount of water is required to assist the crystallization process to obtain smooth pin-hole free morphology. The change in morphology led to improved fill factor in the device, with highest efficiency ~14%, which was significantly higher than devices made from perovskite film without adding water. We also showed that addition of up to 25% by volume of water does not significantly change the device performance.

A novel method was developed to convert the electro-catalytically inactive commercial WO 3 and SnO 2 into high efficient WO 3−x and SnO 2−x counter electrodes for dye sensitized solar cells (DSSs) to replace Pt. Both WO 3 and SnO 2 was treated with Urea with different Urea mass ratio concentrations and annealed under N 2 environment at 500°C. The energy conversion efficiency (PEC) was significantly improved by urea treatment with 8.57% compared to 2.91 % for non-treated CE in case of WO 3 and increases from 2.76 % for non-treated CE to 8.7 % after urea treatment in case of SnO 2 . All other characterizations performed for urea treated WO 3 and SnO 2 support the hypothesis of creating oxygen vacancies inside the metal oxides by the treatment. These oxygen vacancies facilitate the redox process in iodide/trioxide electrolyte. The density of these oxygen vacancies could be controlled by controlling the urea concentration during the treatment.

One of the challenges with organic-inorganic hybrid perovskite films, is its degradation from moisture present in ambient atmosphere, which severely restricts its crystallization process using thermal annealing in ambient air having high humidity levels. A widely used method for perovskite film crystallization is use of thermal annealing in inert atmosphere to rapidly crystallize the film in perovskite phase, immediately after its deposition. Herein, we have explored several methods of crystallization of mixed-halide perovskite (CH 3 NH 3 PbI 3−x Cl x ) film crystallization in ambient air with an aim to obtain high crystallinity and complete conversion to perovskite phase in ambient air assisted with and without thermal annealing. We optimized the crystallization process of perovskite film by exposing the film in ambient air, partially exposure to air followed by thermal annealing, exposing it to air-flow at room temperature. Perovskite films were spin coated inside the N 2 filled glove box and immediately were taken outside in air with 40% relative humidity (RH). Crystallized mixed-halide perovskite films obtained from different approaches were then used to fabricate planar perovskite solar cells with device structure as ITO/PEDOT:PSS/CH 3 NH 3 PbI 3−x Cl x /PC 60 BM/Rhodamine/Ag. It was concluded that humidity plays an important role in crystallization of perovskite films in ambient air, but additional treatment could lead to improved perovskite crystallinity.

An optimal small amount of water added into methyl ammonium iodide (MAI) solution in isopropyl alcohol (IPA) helps perovskite crystallization and leads to larger grain size from sequential deposition of perovskite films. The concentration of water was varied from 1% to 7% (vol% of IPA) in MAI solution and optical absorption, crystallization, morphology of perovskite films and their photovoltaic performance were studied in perovskite solar cells. 5% by volume was found to lead to preferential crystallization in the (110) plane with grain size about three times that of perovskite films prepared without adding water into the MAI solution. The optimal water concentration of 5% by volume in the MAI solution led to average perovskite grain size of ∼600 nm and solar cell efficiency of 12.42% at forward scan with a rate of 0.5 V s(-1). Device performance decreases after increasing water concentration beyond 5% in the MAI solution due to formation of the PbI2 phase. Transient photocurrent and photovoltage measurements show the shortest charge transport time at 0.99 μs and the longest charge carrier life time at 13.6 μs for perovskite films prepared from 5% water in MAI solution, which improved perovskite solar cell efficiency from 9.04% to 12.42%.

In this work, a band pass filter based on frequency selective surface (FSS) is presented. The resonance of the FSS is achieved by perforating slot type ring structure on an Aluminum layer. To ensure adequate mechanical strength, this structure is again supported by a dielectric layer. The physical dimensions of the FSS, i.e. ring radius, slot width, cell dimension and width of the layers all are responsible for the resonance behavior. In its electrical equivalent circuit, these dimensions act as inductor and capacitor. The center frequency of the designed filter is at 0.16 THz with a −3 dB bandwidth of 18 GHz. This filter can be utilized as a part of any THz communication system to achieve application specific frequency discrimination. The simulation has been carried by using commercial software-CST Microwave Studio. The performance of the fabricated FSS is evaluated by Microwave Vector Network Analyzer.

In this paper the performance of a PV driven water pump, without battery storage, for supplemental irrigation by harvesting rainwater is analyzed. A brushless DC motor is used in this work. The worst day, in terms of rainfall, of the month of July has been chosen for data collection. The variation of the flow rate as a function of the PV array power is found to be linear. Head loss is calculated and found greater at higher flow rate. Lower trend of the subsystem efficiency is observed with the increment of the array power. Considering the module efficiency of the manufacturer, the system efficiency is also calculated and found 3.2% as the highest. The amount of water lifted is found to be quite satisfactory for supplemental irrigation.DOI: http://dx.doi.org/10.3329/dujs.v60i1.10333 Dhaka Univ. J. Sci. 60(1): 37-41, 2012 (January)

The role of the metal–active layer interface in photogenerated recombination has been investigated using nanoscale current sensing atomic force microscopy (CS-AFM) and intensity modulated photocurrent spectroscopy (IMPS) in as-deposited, pre-annealed and post-annealed bulk heterojunction (BHJ) solar cells. Aluminum (Al) confined post-annealed BHJ solar cells exhibited a significantly improved device efficiency compared to pre-annealed BHJ solar cells having similar photocarrier harvesting ability in the active layer. The nanoscale topography and CS-AFM results indicate a uniform PCBM rich phase at the metal–active layer interface in the post-annealed cells, but PCBM segregation in the pre-annealed cells. These two different annealing processes showed different carrier dynamics revealed using IMPS under various light intensities. The IMPS results suggest reduced photo generated carrier recombination in uniform PCBM rich post-annealed BHJ solar cells. This study reveals the importance of the metal–bend interface in BHJ solar cells in order to obtain efficient charge carrier extraction for high efficiency.