Browsing by Author "Abate, Seid Yimer"

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Compact TiO2 films with sandwiched Ag nanoparticles as electron-collecting layer in planar type perovskite solar cells: improvement in efficiency and stability
(2018-01-01)
Abate, Seid Yimer
;
Wu, Wen-Ti
;
Pola, Someshwar
;
Tao, Yu-Tai
;
應用化學系
Fabrication of perovskite solar cells (PSCs) in a simple way with high efficiency and stability remains a challenge. In this study, silver nanoparticles (Ag NPs) were sandwiched between two compact TiO2 layers through a facile process of spin-coating an ethanolic AgNO3 solution, followed by thermal annealing. The presence of Ag NPs in the electron-transporting layer of TiO2 improved the light input to the device, the morphology of the perovskite film prepared on top, and eliminated leakage current. Photoluminescence and electron mobility studies revealed that the incorporation of Ag NPs in the ETL of the planar PSC device facilitated the electron-hole separation and promoted charge extraction and transport from perovskite to ETL. Hysteresis-free devices with incorporated Ag NPs gave a high average short-circuit current density (J(sc)) of 22.91 +/- 0.39 mA cm(-2) and maximum power conversion efficiency of 17.25%. The devices also showed enhanced stability versus a control device without embedded Ag NPs. The possible reasons for the improvement are analyzed and discussed.
New Helicene-Type Hole-Transporting Molecules for High-Performance and Durable Perovskite Solar Cells
(2018-12-05)
Lin, Yeo-Sin
;
Abate, Seid Yimer
;
Lai, Kuan-Wen
;
Chu, Chih-Wei
;
Lin, Yan-Duo
Three azahelicene derivatives with electron-rich bis(4-methoxyphenyl)amino or bis(p-methoxyphenyl)aminophenyl groups at the terminals were deliberately designed, synthesized, and characterized as hole-transporting materials (HTMs) for perovskite solar cells (PSCs). Optical and thermal properties, energy level alignments, film morphologies, hole extraction ability, and hole mobility were studied in detail. PSCs using the newly synthesized molecules as HTMs were fabricated. A maximum power conversion efficiency (PCE) of 17.34% was observed for the bis(p-methoxyphenyl)amino-substituted derivative (SY1) and 16.10% for the bis(p-methoxyphenyeaminophenyl-substituted derivative (SY2). Longer-chain substituent such as hexyloxy group greatly diminishes the efficiency. In addition, the dopant-free devices fabricated with SY1 as the HTM shows an average PCE of 12.13%, which is significantly higher than that of spiro-OMeTAD (7.61%). The ambient long-term stability test revealed that after 500 h, the devices prepared from SY1 and SY2 retained more than 96% of its initial performance, which is much improved than the reference device with standard spiro-OMeTAD as the HTM under the same conditions. Detailed material cost analysis reveals that the material cost for SY1 is less than 8% of that for spiro-OMeTAD. These results provide a useful direction for designing a new class of HTMs to prepare highly efficient and more durable PSCs.
Photodegradation of organic dyes and industrial wastewater in the presence of layer-type perovskite materials under visible light irradiation
(2018-08-01)
Gade, Ramesh
;
Ahemed, Jakeer
;
Yanapu, Kalyana Lakshmi
;
Abate, Seid Yimer
;
Tao, Yu-Tai
Layer-type perovskite materials based on A(I)A(II)Ti(2)O(6) (A(I )= Na or Ag or Cu and A(II) = La) system for the degradation of several organic dyes and industrial wastewater under visible-light irradiation are reported. The known perovskite material NaLaTi2O6 (NLTO) was prepared by a new sol-gel process. Ion-exchange of Na+ ions in NLTO with Ag(+ )or Cu2+ ion led to new perovskite AgLaTi2O6 (ALTO) and Cu-0.5 LaTi2O6 (CLTO) respectively. All the new materials were thoroughly characterized by using PXRD, FESEM, HRTEM, UV-vis DRS, IR, XPS and Solid State Photo-luminescence techniques. The new series of materials were utilized for the degradation of Congo Red dye, 4-chlorophenol and 4,4'-bis(2-sulfostyryl)biphenyl as reference pollutants, as well as industrial wastewater. The mineralization process of Congo Red was evaluated through mass spectrometry, which showed that after 60 min of irradiation, the dye degraded with all fragments disappeared. Degradation and mineralization of industrial wastewater was studied by using a newly designed photoreactor via a two-stage process. Mechanistic studies for the fast degradation of Congo Red and industrial wastewater were carried out in the presence of various scavengers. Finally, the photomineralized wastewater was evaluated by chemical oxygen demand (COD) test and the obtained value is close to the standard value. Highest efficiency of degradation was found for ALTO as the photocatalyst, followed by CLTO and then NLTO.