Browsing by Author "Shahbazi, Saeed"

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Ag Doping of Organometal Lead Halide Perovskites: Morphology Modification and p-Type Character
(2017-02-23)
Shahbazi, Saeed
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Tsai, Cheng-Min
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Narra, Sudhakar
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Wang, Chi-Yung
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Shiu, Hau-Shiang
We report a simple synthetic approach to grow uniform CH3NH3PbI3 perovskite (PSK) layers free of pinholes via ciE varied portions of silver iodide (AgI) added to the precursor solution. XRD/EDS elemental mapping experiments demonstrated nearly uniform Ag distribution inside the perovskite film. When the 1% AgI- assisted perovskite films were fabricated into a p-i-n planar device, the a) photovoltaic performance was enhanced by similar to 30% (PCE increased from 9.5% to 12.0%) relative to the standard cell without added AgI. . Measurement of electronic properties using a hall setup indicated that perovskite films show p-type character after Ag doping, whereas the film is n-type without Ag. Transients of photoluminescence of perovskite films with and without AgI additive deposited on glass, p-type (PEDOT:PSS), and n-type (TiO2) contact layers were recorded with a time-correlated single-photon counting (TCSPC) technique. The TCSPC results indicate that addition of AgI inside perovskite in contact with PEDOT:PSS accelerated the hole-extraction motion whereas that in contact with TiO2 led to a decelerated electron extraction, in agreement with the trend observed from the photovoltaic results. The silver cationic dopant inside the perovskite films had hence an effect of controlling the morphology to improve photovoltaic performance for devices with p-i-n configuration.
Application of a natural antioxidant as an efficient strategy to decrease the oxidation in Sn-based perovskites
(2020-12-15)
Mohammadian-Sarcheshmeh, Hamideh
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Mazloum-Ardakani, Mohammad
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Rameez, Mohammad
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Shahbazi, Saeed
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Diau, Eric Wei-Guang
This study aims at the application of uric acid (UA), as a natural antioxidant, an inexpensive and available additive, in the fabrication of Sn-perovskite solar cells (Sn-PSCs). First, we fabricate a carbon structure Sn-PSC without the HTM layer which is more economical and environmentally friendly. Then, we investigate the effect of a UA additive on their performance. An important problem in Sn-PSCs is tin oxidation, producing p-type doping and Sn vacancies in the cells. All of these lead to serious device deterioration and low performance. In this case, adding UA helps to improve the photovoltaic parameters and, in particular, the device performance as a result of an effective decrease in Sn2+ oxidation and carrier recombination. Also, the device stability improves, in comparison to devices not treated with UA. According to the findings of this study, the UA can replace some expensive additives to prevent tin oxidation and significantly improve photovoltaic parameters. (C) 2020 Elsevier B.V. All rights reserved.
Development of Novel Mixed Halide/Superhalide Tin-Based Perovskites for Mesoscopic Carbon-Based Solar Cells
(2020-04-02)
Rameez, Mohammad
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Shahbazi, Saeed
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Raghunath, Putikam
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Lin, Ming Chang
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Hung, Chen Hsiung
Tin perovskites suffer from poor stability and a self-doping effect. To solve this problem, we synthesized novel tin perovskites based on superhalide with varied ratios of tetrafluoroborate to iodide and implemented them into solar cells based on a mesoscopic carbon-electrode architecture because film formation was an issue in applying this material for a planar heterojunction device structure. We undertook quantum-chemical calculations based on plane-wave density functional theory (DFT) methods and explored the structural and electronic properties of tin perovskites FASnI(3-x)(BF4)(x) in the series x = 0, 1, 2, and 3. We found that only the x = 2 case, FASnI(BF4)(2), was successfully produced, beyond the standard FASnI(3). The electrochemical impedance and X-ray photoelectron spectra indicate that the addition of tin tetrafluoroborate instead of SnI2 suppressed trap-assisted recombination by decreasing the Sn4+ content. The power conversion efficiency of the FASnI(BF4)(2) device with FAI and Sn(BF4)(2) in an equimolar ratio improved 72% relative to that of a standard FASnI(3) solar cell, with satisfactory photostability under ambient air conditions.
Efficiency and Stability Enhancement of Fully Ambient Air Processed Perovskite Solar Cells Using TiO2 Paste with Tunable Pore Structure
(1970-01-01)
Seyed-Talebi, Seyedeh Mozhgan
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Kazeminezhad, Iraj
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Shahbazi, Saeed
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Diau, Eric Wei-Guang
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交大名義發表
Crystallization and nucleation of the perovskite layer in the mesoscopic perovskite solar cells (PSCs) depend on the nucleation sites of the electron transport layer (ETL). The porosity optimization of TiO2 film as an efficient ETL plays an important role in the performance improvement of PSCs. In the present study, nontoxic carbon spheres synthesized with uniform morphology and controllable size under hydrothermal conditions and used as a template to generate the tunable porous TiO2 films. Furthermore, the effect of porosity modification of TiO2 on the formation of perovskite films with large grain size is studied in an ambient atmosphere with humidity higher than 50%. The best TiO2 film is produced with carbon spheres 8 wt% (C8), which results in the formation of a pinhole-free, and compact-packed perovskite layer. The fully air processed PSC device with the ETL made of C8 film exhibits an efficiency of 16.66% with reduced hysteresis, which is much superior in performance compared to the standard cell (11.72%). It is believed that this porosity optimization of TiO2 layer is a simple practical strategy for improved stability of fully air processed efficient perovskite solar cells and usable for the fabrication of reproducible compact perovskite layers in uncontrolled laboratories.
Realizing a Cosolvent System for Stable Tin-Based Perovskite Solar Cells Using a Two-Step Deposition Approach
(2020-08-14)
Shahbazi, Saeed
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Li, Meng-Yu
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Fathi, Amir
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Diau, Eric Wei-Guang
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交大名義發表
Applying a two-step procedure and solvent engineering, we fabricated a stable tin-based perovskite, formamidinium tin triiodide (FASnI(3)), solar cell for lead-free photovoltaic applications. The first step was deposition of a SnI2 layer with the solvent dimethyl sulfoxide; the second step was application of a cosolvent system containing hexafluoro-2-propanol (HFP), isopropyl alcohol (IPA), and chlorobenzene (CB) in a 5:5:2 ratio to deposit the FAI layer on the SnI2 layer. The traditional IPA solvent prevented the formation of a stable FASnI(3) layer such that a stable device could not be fabricated. HFP was hence used to form hydrogen bonds with IPA and FM to retard the crystal growth of FASnI(3); CB served as the antisolvent. Ethylenediammonium dihypophosphite in the first step was an effective reducing agent to increase the efficiency of power conversion from similar to 5% to similar to 7% with great reproducibility and stability over 4000 h.