Browsing by Author "Rameez, Mohammad"

Now showing 1 - 5 of 5

Application of a natural antioxidant as an efficient strategy to decrease the oxidation in Sn-based perovskites
(2020-12-15)
Mohammadian-Sarcheshmeh, Hamideh
;
Mazloum-Ardakani, Mohammad
;
Rameez, Mohammad
;
Shahbazi, Saeed
;
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 Hybrid Pseudohalide Tin Perovskites for Highly Stable Carbon-Electrode Solar Cells
(2020-05-13)
Rameez, Mohammad
;
Lin, Eric Yan-Ru
;
Raghunath, Putikam
;
Narra, Sudhakar
;
Song, Donghoon
Tin-based perovskites degrade rapidly upon interaction with water and oxygen in air because Sn-I bonds are weak. To address this issue, we developed novel tin perovskites, FASnI((3-x))(SCN)(x) (x = 0, 1, 2, or 3), by employing a pseudohalide, thiocyanate (SCN-), as a replacement for halides and as an inhibitor to suppress the Sn2+/Sn4+ oxidation. The structural and electronic properties of pseudohalide tin perovskites in this series were explored with quantum-chemical calculations by employing the plane-wave density functional theory (DFT) method; the corresponding results are consistent with the experimental results. Carbon-based perovskite devices fabricated with tin perovskite FASnI(SCN)(2) showed about a threefold enhancement of the device efficiency (2.4%) relative to that of the best FASnI(3)-based device (0.9%), which we attribute to the improved suppression of the formation of Sn4+, retarded charge recombination, enhanced hydrophobicity, and stronger interactions between Sn and thiocyanate for FASnI(SCN)(2) than those for FASnI(3). After the incorporation of phenylethyleneammonium iodide (PEAI, 10%) and ethylenediammonium diiodide (EDAI(2), 5%) as coadditives, the FASnI(SCN)(2) device gave the best photovoltaic performance with J(SC) = 20.17 mA cm(-2), V-OC = 322 mV, fill factor (FF) = 0.574, and overall efficiency of power conversion PCE = 3.7%. Moreover, these pseudohalide-containing devices display negligible photocurrent-voltage hysteresis and great stability in ambient air conditions.
Development of Novel Mixed Halide/Superhalide Tin-Based Perovskites for Mesoscopic Carbon-Based Solar Cells
(2020-04-02)
Rameez, Mohammad
;
Shahbazi, Saeed
;
Raghunath, Putikam
;
Lin, Ming Chang
;
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.
Slow surface passivation and crystal relaxation with additives to improve device performance and durability for tin-based perovskite solar cells
(2018-09-01)
Jokar, Efat
;
Chien, Cheng-Hsun
;
Fathi, Amir
;
Rameez, Mohammad
;
Chang, Yu-Hao
We investigated the doping effect of bulky organic cations with ethylenediammonium diiodide (EDAI(2)) and butylammonium iodide (BAI) as additives to passivate surface defects, to control the film morphology and to improve the crystallinity for inverted planar FASnI(3) perovskite solar cells. The addition of BAI altered significantly the orientation of crystal growth and improved the connectivity of the crystal grains, but the existence of pinholes in the surface of the pristine FASnI(3) films was unavoidable; this effect impeded further improvement of the device performance (PCE 5.5%), which is nevertheless superior to that of a pristine FASnI(3) film (PCE 4.0%). The addition of EDAI(2) had the effect of curing the pinhole problem, passivating the surface defect states, preventing Sn2+/Sn4+ oxidation and inducing slow relaxation of the crystal structure. In the presence of the EDAI(2) additive (1%), the FASnI(3) device attained the best initial efficiency, 7.4%, and the device performance continuously increased as a function of duration of storage; the maximum PCE, 8.9%, was obtained for a device stored in a glove box for over 1400 h with only slight degradation for storage beyond 2000 h. The observed slow passivation of surface defects and relaxation of crystal strain were verified with X-ray diffraction, X-ray photoelectron spectroscopy and photoluminescence decay techniques.
Strategies To Improve Performance and Stability for Tin-Based Perovskite Solar Cells
(2019-08-01)
Diau, Eric Wei-Guang
;
Jokar, Efat
;
Rameez, Mohammad
;
交大名義發表
;
應用化學系
This Perspective reviews the developments of tin-based perovskite solar cells (PSCs) during the period 2014-2019 based on two organic cations (methylammonium vs formamidinium) and two device architectures (normal vs inverted) with the strategies of using cocations and coadditives. Unlike their lead-based analogues, tin-based PSCs suffer from the problems of Sn2+/Sn4+ oxidation and film formation. The current best cell is based on an inverted planar FASnI(3) device with guanidinium as cocation, SnF2 as additive, and ethyl-enediammonium iodide as coadditive, which attains record efficiency near 10% with great stability. The device stability and performance might be further improved upon introducing bulky organic cations with a suitable coadditive to form a hybrid 2D/3D crystal structure. Considering the theoretical limit on device efficiency for tin-based PSCs to be, similar to 33%, there is much room for further performance improvement if the problems can be resolved according to the approaches discussed in this Perspective.