Browsing by Author "Chien, Cheng-Hsun"

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Robust Tin-Based Perovskite Solar Cells with Hybrid Organic Cations to Attain Efficiency Approaching 10%
(2019-01-01)
Jokar, Efat
;
Chien, Cheng-Hsun
;
Tsai, Cheng-Min
;
Fathi, Amir
;
Diau, Eric Wei-Guang
The stability of a tin-based perovskite solar cell is a major challenge. Here, hybrid tin-based perovskite solar cells in a new series that incorporate a nonpolar organic cation, guanidinium (GA(+)), in varied proportions into the formamidinium (FA(+)) tin triiodide perovskite (FASnI(3)) crystal structure in the presence of 1% ethylenediammonium diiodide (EDAI(2)) as an additive, are reported. The device performance is optimized at a precursor ratio (GAI:FAI) of 20:80 to attain a power conversion efficiency (PCE) of 8.5% when prepared freshly; the efficiencies continuously increase to attain a record PCE of 9.6% after storage in a glove-box environment for 2000 h. The hybrid perovskite works stably under continuous 1 sun illumination for 1 h and storage in air for 6 days without encapsulation. Such a tin-based perovskite passes all harsh standard tests, and the efficiency of a fresh device, 8.3%, is certified. The great performance and stability of the device reported herein attains a new milestone for lead-free perovskite solar cells on a path toward commercial development.
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.