Key Engineering Materials Vol. 860

Abstract: We have studied the effect of lead (II) cyanate Pb (OCN)₂ additive on photovoltaic properties of inverted planar solar cells based on inorganic-organic hybrid perovskite CH₃NH₃PbI₃. The active layers of the solar cells were fabricated with a reaction between CH₃NH₃I and a mixture of PbI₂ and Pb (OCN)₂. The highest power conversion efficiency was 15%. Hysteresis behaviors in JV curves were reduced. The lifetime of the solar cells was dramatically increased. SEM images indicated that crystallite sizes were enlarged. The OCN groups were not incorporated into crystals from infrared measurements. These results suggest that Pb (OCN)₂ affect mainly the crystallization process of CH₃NH₃PbI₃.

Abstract: Perovskite solar cells have a great potential as competitor of silicon solar cells which have been dominated the market of solar cells since last decade, due to a tremendous improvement of their power conversion efficiency (PCE). Recently, a PCE of perovskite solar cells above 23% have been obtained. Moreover, perovskite solar cells can be fabricated using simple solution methods, therefore, the whole cost production of solar cells is less than half of silicon solar cells. However, their low stability in thermal and high humidity hinder them to be produced and commercially used to replace silicon solar cells. Many efforts have been done to improve both PCE and stability, including mixed inorganic-organic cations, mixed halide anions, improvement of perovskite morphology or crystallinity and using small molecules for passivation of defect in perovskite. In this paper, we used mixed cesium-methylammonium to improve both PCE and stability of perovskite solar cells. Cesium was used due to its smaller ionic radius than methylammonium (MA) ions, therefore, the crystal structure of perovskite is not distorted. Moreover, perovskite cesium-lead-bromide (CsPbBr₃) are more stable than that of MAPbBr₃ and doping cesium increased light absorption in perovskite MAPbBr₃. We studied the effect of mixed cesium-MA on the PCE and stability at high humidity (>70%). The percentage of cesium was varied at 0%, 5%, 10%, 15% and 20%. The perovskite solar cells have monolithic hole-transport layer free (HTL-free) structure using carbon as electrode. This structure was used due simple and low cost in processing of solar cells. Our results showed that by replacing 10% of MA ions with Cs ions, both PCE and stability at high humidity are improved.

Abstract: The third generation of photovoltaic, called as dye-sensitized solar cells (DSSC) have attracted much attention and currently become an interesting research topics. One important part of DSSC that determines its performance is photoanodes. Recently, graphene has been used to enhance the efficiency of DSSC through the increasing of electronic transportation. Introduction of graphene into DSSC is realized by changing the form of graphene oxide (GO) into reduced graphene oxide (rGO) through the reduction process. In this work, DSSC based on TiO₂ photoanodes modified by rGO were fabricated. rGO layer was deposited on TiO₂ mesoporous layer using UV-oven spraying method. We found that parameters of DSSC such as open circuit voltage, short circuit current and fill factor increase with the incorporation of rGO layer in TiO₂photoanodes. DSSC with TiO₂/rGO photoanodes has the highest power conversion efficiency of 11.01% which contributed from the enhancement of short circuit current. The rGO layer found to be an effective layer to block charge recombination in photoanode.

Abstract: Over the past few years, metal halide perovskites have been considered as a promising material for application in photovoltaic devices because of its unique optical and electrical properties. In particular, Sn-based perovskites have been being considered to replace Pb-based perovskite because of the Pb toxicity that will raise serious concerns on the environmental issue. In this report, we present our attempt to synthesize the Sn-based perovskite (namely, Cs₂SnI₆), which is air and thermal stable, and use it as an electron transport layer in dye-sensitized solar cells (DSSC) for improving its power conversion efficiency. The synthesize of Cs₂SnI₆ perovskite was done by mixing Cs₂CO₃ in HI and SnI₄ in ethanol to form a precipitate at room temperature. The purification process was an important part to collect effectively the synthesis product. The fabrication of DSSC was done by a standard process based on the screen printing and spin-coating techniques, while the characterization of Cs₂SnI₆ was done by UV-Vis spectroscopy and XRD measurement. In the present experiment, the addition of the Cs₂SnI₆ layer was performed by spin coating the Cs₂SnI₆ solution onto the TiO₂ mesoporous layer. The photovoltaic performance of the fabricated DSSC shows a significant enhancement in the short circuit photocurrent density (J_sc) and conversion efficiency, that is, from 15.04 mA/cm² to 16.33 mA/cm² from 5.7% to 6.75% due to the incorporation of spin-coated 5 mM Cs₂SnI₆ in comparison to the reference cell without Cs₂SnI₆.

Abstract: In recent years, perovskite material has been extensively studied due to its unique physical properties and promising application in the third generation of solar cells. In particular, Sn-based perovskite has been considered to replace Pb-based perovskite because of the toxic effects and it can lead to other serious problems related to the environment. Cs₂SnI₆ perovskite has been known to be synthesized in a simple chemical process and it can be produced on a large scale. Moreover, this material is also oxygen and moisture stable due to the high oxidation state of tin. In this study, we synthesize air-stable Cs₂SnI₆ perovskite by the use of the wet chemical process at room temperature. Next, we attempt to fabricate the inverted bulk heterojunction solar cells incorporated Cs₂SnI₆ as electron transport layer in the configuration of ITO/ZnO/Cs₂SnI₆/P3HT:PCBM/PEDOT:PSS/Ag to improve device performance. The Cs₂SnI₆ perovskite shows an Fm-3m space group with a cubic lattice parameter of 11.62Å confirmed by X-Ray Diffraction (XRD) measurement, while UV-Vis measurement indicates this type of perovskite has direct band gap ~3.1 eV. The fabricated solar cell device reveals the enhancement in current density at short circuit condition (J_sc) from 64.69 mA/cm² to 77.02 mA/cm² with the addition of 2.25 mg/ml Cs₂SnI₆ along with the enhancement of power conversion efficiency (PCE) from 7.05% to 9.75% as characterized by J-V measurement. In our case, the voltage at open circuit condition (V_oc) of the device does not perform significant improvement. Besides, it is found that the solar cell devices are quite stable even after exposure in the air for six weeks after fabrication, as indicated by PCE performance.

Abstract: We attempt to study the effect of gold nanoparticles embedded into the active polymer of regioreguler poly (3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) on the charge kinetic to enhance the performance of bulk-heterojunction solar cell. It has been known that the generation of localized surface plasmon resonance (LSPR) would both increase the photon absorption and improve the efficiency of charge separation. Synthesis of gold nanoparticles stabilized by oleylamine (AuOA) was carried out by reduction method and resulted in the spherical shape of nanoparticles with a diameter size of ~12 nm. The absorbance spectra show the typical of surface plasmon peak of AuOA in solution at ~527 nm. Fabrication of inverted bulk-heterojunction solar cell device was done in the configuration of ITO/ZnO/P3HT:PCBM:AuOA/PEDOT:PSS/Ag. Incorporation of AuOA in polymer solution is clearly detected from the enhanced absorbance peak resulted from UV-Vis measurement and the mix solution of P3HT:PCBM:AuOA is quite stable in the concentration of AuOA less than 10 wt%. In our experiment, fabricated solar cell reveals the enhancement in current density at short circuit condition (J_sc) from 44.57 mA/cm² to 56.14 mA/cm² with the addition of 3.9 wt% AuOA in polymer solution along with the enhancement of power conversion efficiency (PCE) from 4.07% to 6.23% as characterized by J-V measurement. In our case, the voltage at open circuit condition (V_oc) of the device does not show significant improvement.

Abstract: This paper reports the preliminary study on the synthesis of Ni doped CZTS (Cu₂ZnSnS₄:Ni) particle 5 at.% of Cu by solution method and dispersion of the obtained particles by beads mill method at various dispersing agents (SDS, CTAB, and Tween80). The phase transformation of the obtained particles was analyzed from the XRD spectra and XRF elemental analysis. The phase transformation and amount of Ni-doped to particles was predicted employing commercially available analytical software tool Match! Version 2.x. Moreover, the dispersion characteristics were investigated includes size, size distribution, and zeta potential of bare particles in comparison to various dispersing agents. This characteristic related to the future application of CZTS as an absorber in a thin-film based PV. The XRD analysis showed that the obtained particle contained crystal structure of copper sulfate pentahydrate (75.9 %), Ni(HN₂S₂)₂ (12.5 %), and Cu₂ZnSnS₄ (11.6%). The XRF elemental analysis showed that amount of Ni-doped was 6.8 at.%; it was higher than the initial design amount of Ni doping. The dispersion of suspended particles was the majority (90%) with an average size of 3.06 µm and only 10 % with size 255 nm. Beads-milling of particles without dispersing agents did not disintegrate agglomerated particles. It is highlighted dispersion only using magnetic stirred with SDS dispersing agent provides the best suspension with a majority (60%) in 166 nm and only 30 % with average size 3.06 µm with relatively high zeta potential (-17 mV). It was concluded that the presence of a multi-phase crystal needs to be resolved either by proper calcination at a higher temperature than 400°C or further heating at a higher temperature during film preparation. High-energy centrifugation of zirconia beads mill caused desorption of adsorbed steric stabilization of dispersing agent under investigation. Further investigation on the coating process to facilitated laboratory fabrication of thin-film absorber with SDS as a dispersing agent is necessary to carry out concerning the properties of the thin-film.

Abstract: Supercapacitor is an electronic device with characteristic of having higher power density than battery and higher energy density than conventional capacitor. In order to achieve exceptional power and energy density, it is necessary to use materials with high specific surface area as its electrodes. In this study, we prepared a rolled supercapacitor device model using carbon sheet as the electrodes and 1 M KCl electrolyte. A carbon sheet was soaked in 1 M KCl and assembled as a rolled supercapacitor device model. Performance of the rolled supercapacitor device model was measured using a cyclic voltammetry (CV) in a voltage range of-0.8 V to +0.1 V with scan rate variations of 1 mV/s, 5 mV/s, 10 mV/s, 15 mV/s and 20 mV/s. Cyclic voltammetry measurement provide results as follows, E_sp = 0.289 to 0.103 Wh/kg and P_sp = 5.024 to 35.738 W/kg. By using Ragone plot we found that the prepared rolled supercapacitor using carbon-sheet as electrodes had met criteria of supercapacitor. The result show that the carbon sheet has a good prospect to be used as electrodes for rolled supercapacitor.

Abstract: Banana (Musa acuminate) is one of the important fruit crop cultivated in Indonesia. Banana stems is waste biomass form banana farming which the amount is very abundant. Recently, the banana stems waste was used for animal feed, but the amount is small, mostly goes as waste. Banana stems have a high cellulose and hemicellulose content, more than 60%, which made it useful for row material of Carboxymethyl Cellulose (CMC). In this paper, we synthesized CMC from banana stems and apply it as binder in the electrodes of lithium ion battery. The steps of synthesizing CMC from banana stems started with the isolation of the cellulose, then followed by the processes of alkalization, carboxymethylation and finally the purification. FTIR spectrum shows the absorption bands at 3427 cm^-1, 2928 cm^-1, 1613 cm^-1 and 1420 cm^-1 which indicated the successfully of CMC synthesized. The presence of strong absorption bands at 1613 cm^-1 and 1420 cm^-1 are related to the stretching vibration of the carboxyl group (COO-) and (COO-Na). The peak absorption at around 2928 cm^-1 is due to stretching vibration of all hydrocarbon constituent in CMC. While the broad absorption around 3427 cm^-1 is due to the stretching vibration of the hydroxyl groups (-OH). The purity test of CMC mesh-100 is resulting the purity values of 99.84%. These results prove that CMS has actually been formed with high purity. In the application of CMC as anode binder, the best composition is 3 % CMC, where it gives the highest conductivity of 0.457 S/cm. Voltammogram cyclic measurement with a scan rate of 50 mV/s in the voltage range of -1.2 to 1.2 Volt gives the capacitance value of 18 mF.