Browsing by Author "Li, Jia-Xing"

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Crystalline Engineering Toward Large-Scale High-Efficiency Printable Cu(In,Ga)Se-2 Thin Film Solar Cells on Flexible Substrate by Femtosecond Laser Annealing Process
(2017-04-26)
Chen, Shih-Chen
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She, Nian-Zu
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Wu, Kaung-Hsiung
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Chen, Yu-Ze
;
Lin, Wei-Sheng
Ink-printing method emerges as a viable way for manufacturing large-scale flexible Cu(In,Ga)Se-2 (CIGS) thin film photovoltaic (TFPV) devices owing to its potential for the rapid process, mass production, and low-cost nonvacuum device fabrication. Here, we brought the femtosecond laser annealing (fs-LA) process into the ink-printing CIGS thin film preparation. The effects of fs-LA treatment on the structural and optoelectronic properties of the ink-printing CIGS thin films were systematically investigated. It was observed that, while the film surface morphology remained essentially unchanged under superheating, the quality of crystallinity was significantly enhanced after the fs-LA treatment. Moreover, a better stoichiometric composition was achieved with an optimized laser scanning rate of the laser beam, presumably due to the much reduced indium segregation phenomena, which is believed to be beneficial in decreasing the defect states of In-se, V-Se, and In-cu. Consequently, the shunt leakage current and recombination centers were enhancement in photovoltaic conversion efficiency. both greatly decreased, resulting in a near 20%
Dual nanocomposite carrier transport layers enhance the efficiency of planar perovskite photovoltaics
(2018-01-01)
Lin, Hsi-Kuei
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Li, Jia-Xing
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Wang, Hao-Cheng
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Su, Yu-Wei
;
Wu, Kaung-Hsiung
In photovoltaic devices, more effective transfer of dissociated electrons and holes from the active layer to the respective electrodes will result in higher fill factors and short-circuit current densities and, thus, enhanced power conversion efficiencies (PCEs). Planar perovskite photovoltaics feature an active layer that can provide a large exciton diffusion length, reaching several micrometers, but require efficient carrier transport layers for charge extraction. In this study, we employed two nanocomposite carrier transfer layersan electron transport layer (ETL) comprising [6,6]phenyl-C-61-butyric acid methyl ester (PC61BM) doped with the small molecule 4,7-diphenyl-1,10-phenanthroline (Bphen), to enhance the electron mobility, and a hole transfer layer (HTL) comprising poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) doped with molybdenum disulfide (MoS2) nanosheets, to enhance the hole mobility. We used ultraviolet photoelectron spectroscopy to determine the energy levels of these composite ETLs and HTLs; atomic force microscopy and scanning electron microscopy to probe their surface structures; and transmission electron microscopy and synchrotron grazing-incidence small-angle X-ray scattering to decipher the structures of the ETLs. Adding a small amount (less than 1%) of Bphen allowed us to tune the energy levels of the ETL and decrease the size of the PC61BM clusters and, therefore, generate more PC61BM aggregation domains to provide more pathways for electron transport, leading to enhanced PCEs of the resulting perovskite devices. We used quantitative pump-probe data to resolve the carrier dynamics from the perovskite to the ETL and HTL, and observed a smaller possibility of carrier recombination and a shorter injection lifetime in the perovskite solar cell doubly modified with carrier transport layers, resulting in an enhancement of the PCE. The PCE reached 16% for a planar inverted perovskite device featuring an ETL incorporating 0.5 wt% Bphen within PC61BM and 0.1 wt% MoS2 within PEDOT:PSS; this PCE is more than 50% higher than the value of 10.2% for the corresponding control device.
Energy transfer within small molecule/conjugated polymer blends enhances photovoltaic efficiency
(2017-09-14)
Lin, Yu-Che
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Su, Yu-Wei
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Li, Jia-Xing
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Lin, Bo-Hsien
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Chen, Chung-Hao
In this study, we employed ternary blends capable of energy transfer-a synthesized high-band-gap small molecule (SM-4OMe) comprising benzodithiophene (BDT) and rhodanine units (a molecular structure that was designed for energy transfer), a low-band-gap polymer (PTB7-TH) comprising BDT and thienothiophene units with desired packing orientation, and a fullerene-as active layers for singlejunction photovoltaic devices. The light absorption of the small molecule and the polymer was partially complementary, owing to their band gap difference, thereby broadening the absorption spectrum of solar light while maintaining the energy band structures that facilitated energy and charge transfer. The synthesized small molecule SM-4OMe and the PTB7-TH had somewhat similar chemical structureswith the same planar BDT donor units-and thus allowed sufficient mixing between them for energy transfer to take place. The power conversion efficiency of a device incorporating a ternary blend of PTB7-TH:SM-4OMe:PC71BM (0.9 :0.1 :1.5, w/w/w) as the active layer, processed with diiodooctane (2 vol%) in chlorobenzene, was 10.4%, which is higher than the value of 8% of the corresponding device incorporating PTB7-TH:PC71BM (1 :1.5, w/w)-an increase of 30%. We attribute this enhancement to the energy transfer from the high-band-gap small molecule SM-4OMe to the low-band-gap polymer PTB7-TH and to the optimal phase-separated bulk heterojunction morphology that comprises a mean PC71BM cluster size of 6 nm, which is lower than 12 nm for the PTB7-TH and PC71BM binary blends, and slightly better in-plane packing, arising from the inducements of the presence of SM-4OMe. This approach provides a facile and effective way to enhance the power conversion efficiency of single junction organic photovoltaics.
Enhancing performance of ternary blend photovoltaics by tuning the side chains of two-dimensional conjugated polymer
(2019-08-01)
Chen, Chung-Hao
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Lu, Yi-Ju
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Su, Yu-Wei
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Lin, Yu-Che
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Lin, Hsi-Kuei
We prepared the ternary blends active layer by incorporating a new two-dimensional donor-acceptor (D/A) conjugated polymer (BDTTBO) comprising benzo-dithiophene-thiophene-thiophene-benzo oxadiazole chemical units that has three different conjugated side chains bithiophene (BT), benzothiophene (BzT) and thienothiophene (TT) BDTTBO-BT, BDTTBO-BzT and BDTTBO-TT into poly (benzodithiophene-fluorothienothiophene) (PTB7-TH) and PC71BM as for organic photovoltaics (OPVs). We expected that incorporating these BDTTBO with different side chains into the blend of PTB7-TH and PC71BM not only can broaden the absorption of solar spectrum thereby increasing short-circuit current density but also tune the packing of PTB7-TH and the dispersion of PC71BM. In particular, we found that incorporating 10% of BDTTBO-BT to form the PTB7-TH:BDTTBO-BT:PC71BM ternary blend (active layer) device could improve the power conversion efficiency to 10.4% from 9.0% for the binary blend of PTB7-TH:PC71BM device-a relative increase of 15%. We examined the packing orientations of the PBDTTBO:PTB7-TH:PC71BM ternary blend films using synchrotron two-dimensional grazing-incidence wide-angle X-ray scattering, and found that the incorporation of 10% relatively higher crystallinity PBDTTBO-BT, PBDTTBO-BzT or PBDTTBO-TT not only altered the packing orientation of PTB7-TH substantially but also reduced PC71BM cluster size in the ternary blend system, as compared to that in the case of PTB7-TH with PC71BM binary blend, thereby providing more pathways for electrons and thus enhancing the carrier transport in the ternary blend, as evidenced by the carrier mobility.
Enhancing photovoltaic performance by tuning the domain sizes of a small-molecule acceptor by side-chain-engineered polymer donors
(2019-02-21)
Lin, Yu-Che
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Lu, Yi-Ju
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Tsao, Cheng-Si
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Saeki, Akinori
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Li, Jia-Xing
This paper reports two new fluorine-substituted polymer donors (BO2FC8, BO2FEH), with different side-chain architectures, and a new chlorine-substituted small-molecule acceptor (m-ITIC-OR-4Cl) that are capable of simultaneous charge and energy transfer as the binary blend active layer for organic photovoltaics. We first resolved the single-crystal structure of m-ITIC-OR-4Cl and then used simultaneous grazing-incidence wide-and small-angle X-ray scattering to decipher the multi-length-scale structures-such as the shape and size of aggregated domains and molecular orientation-of the blends of BO2FEH and BO2FC8 with m-ITIC-OR-4Cl. The linear side chains of BO2FC8 facilitated its packing and, thus, induced m-ITIC-OR-4Cl to form smaller disc-shaped aggregated domains (thickness: 2.9 nm) than its aggregate domain (thickness: 5.4 nm) in the blend of the branched BO2FEH. That is, the binary blend system of linear-side-chain BO2FC8 with m-ITIC-OR-4Cl featured larger interfacial areas and more pathways for charge transfer and transport, as evidenced by their carrier mobilities. The highest power conversion efficiency (PCE) of 11.0% was that for the BO2FC8: m-ITIC-OR-4Cl device, being consistent with the predicted PCE of 11.2% using machine learning based on random forest algorism; in comparison, the PCE of the BO2FEH:m-ITIC-OR-4Cl device was 6.4%. This study has not only provided insight into the photovoltaic performances of new polymer donor/small-molecule acceptor blends but has also, for the first time, deciphered the hierarchical morphologies-from molecule orientation to nano-domain shape and size-of such blend systems, linking the morphologies to the photovoltaic performances. The use of side-chain architectures suggests an approach for tuning the morphology of the polymer/small-molecule binary blend active layer for use in organic photovoltaics.
Improving Crystalline Quality of Non-Vacuum Processed Cu(In,Ga) Se-2 Thin Films by Femtosecond Laser Annealing
(2016)
Li, Jia-Xing
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She, Nian-Zu
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Chang, Yu-Hsuan
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Chen, Shih-Chen
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Kuo, Hao-Chung
We demonstrate the advantages of femtosecond laser annealing on non-vacuum CIGS thin films. The PL spectra implied some defect-levels or band-fluctuations were eliminated, and the conversion efficiency and ideal factor were enhanced after laser annealing.
In-Situ Probing Plasmonic Energy Transfer in Cu(In, Ga)Se-2 Solar Cells by Ultrabroadband Femtosecond Pump-Probe Spectroscopy
(2015-12-18)
Chen, Shih-Chen
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Wu, Kaung-Hsiung
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Li, Jia-Xing
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Yabushita, Atsushi
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Tang, Shih-Han
In this work, we demonstrated a viable experimental scheme for in-situ probing the effects of Au nanoparticles (NPs) incorporation on plasmonic energy transfer in Cu(In, Ga)Se-2 (CIGS) solar cells by elaborately analyzing the lifetimes and zero moment for hot carrier relaxation with ultrabroadband femtosecond pump-probe spectroscopy. The signals of enhanced photobleach (PB) and waned photoinduced absorption (PIA) attributable to surface plasmon resonance (SPR) of Au NPs were in-situ probed in transient differential absorption spectra. The results suggested that substantial carriers can be excited from ground state to lower excitation energy levels, which can reach thermalization much faster with the existence of SPR. Thus, direct electron transfer (DET) could be implemented to enhance the photocurrent of CIGS solar cells. Furthermore, based on the extracted hot carrier lifetimes, it was confirmed that the improved electrical transport might have been resulted primarily from the reduction in the surface recombination of photoinduced carriers through enhanced local electromagnetic field (LEMF). Finally, theoretical calculation for resonant energy transfer (RET)-induced enhancement in the probability of exciting electron-hole pairs was conducted and the results agreed well with the enhanced PB peak of transient differential absorption in plasmonic CIGS film. These results indicate that plasmonic energy transfer is a viable approach to boost high-efficiency CIGS solar cells.
Origin of Extended UV Stability of 2D Atomic Layer Titania-Based Perovskite Solar Cells Unveiled by Ultrafast Spectroscopy
(2019-06-19)
Thilakan, Anusha Puliparambil
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Li, Jia-Xing
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Chen, Tzu-Pei
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Li, Shao-Sian
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Chen, Chun-Wei
The inherent instability of UV-induced degradation in TiO2-based perovskite solar cells was largely improved by replacing the anatase-phase compact TiO2 layer with an atomic sheet transport layer (ASTL) of two-dimensional (2D) Ti1-delta O2. The vital role of microscopic carrier dynamics that govern the UV stability of perovskite solar cells was comprehensively examined in this work by performing time-resolved pump-probe spectroscopy. In conventional perovskite solar cells, the presence of a UV-active oxygen vacancy in compact TiO2 prohibits current generation by heavily trapping electrons after UV degradation. Conversely, the dominant vacancy type in the 2D Ti1-delta O2 ASTL is a titanium vacancy, which is a shallow acceptor and is not UV-sensitive. Therefore, it significantly suppresses carrier recombination and extends UV stability in perovskite solar cells with a 2D Ti1-delta O2 ASTL. Other carrier dynamics, such as electron diffusion, electron injection, and hot hole transfer processes, were found to be less affected by UV irradiation. Quantitative pump-probe data clearly show a correlation between the carrier dynamics and UV aging of perovskite solar cells, thus providing a profound insight into the factors driving UV-induced degradation in perovskite solar cells and the origin of its performance.