Browsing by Author "Diau, Eric Wei-Guang"

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A Collection of Special Efforts on DSSC in 2009 Preface
(2010-10-01)
Wang, Hong-Wen
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Diau, Eric Wei-Guang
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應用化學系
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應用化學系分子科學碩博班
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Department of Applied Chemistry
A Direct Mapping Approach to Understand Carrier Relaxation Dynamics in Varied Regions of a Polycrystalline Perovskite Film
(1970-01-01)
Fathi, Amir
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Jokar, Efat
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Lee, Yuan-Pern
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Diau, Eric Wei-Guang
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交大名義發表
We developed a direct mapping approach to overlay the image of a polycrystalline perovskite film obtained from the transient absorption microscope (TAM) with that from the scanning electron microscope (SEM). By mapping these imaging data pixel by pixel, we are able to observe the relaxation dynamics of the photo-generated charge carriers on varied regions of the film. The carrier relaxation dynamics contain a dominated single-exponential decay component owing to the recombination of charge carriers. The lifetime distribution of charge recombination shows a bimodal feature, for which the rapid and slow distributions are assigned as free and trapped carriers, respectively. The charge recombination was slower in the grain boundary (GB) region than in the grain interior (GI) region. The small grains have longer lifetimes than the large grains for the crystal size smaller than 500 nm. Therefore, GB with retarded charge recombination might play a positive role in a perovskite solar cell.
A fluorene-modified porphyrin for efficient dye-sensitized solar cells
(2012)
Wu, Cheng-Hua
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Pan, Tsung-Yu
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Hong, Shang-Hao
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Wang, Chin-Li
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Kuo, Hshin-Hui
Porphyrins bearing a polyaromatic or a heterocyclic group are prepared to study their fundamental and photovoltaic properties. Solar cells sensitized with a fluorene-modified porphyrin outperform other dyes in the series, reaching similar to 90% efficiency of N719 dye.
A mechanism for the formation of annealed compact oxide layers at the interface between anodic titania nanotube arrays and Ti foil
(2009-06-01)
Chen, Chien-Chon
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Say, Wen C.
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Hsieh, Sheng-Jen
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Diau, Eric Wei-Guang
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應用化學系
We propose a mechanism for the growth of crystalline anodic titanium-oxide (ATO) nanochannel arrays based on thermodynamic considerations and structural imperfections. Both amorphous and crystalline ATO films were obtained from the anodization of a titanium foil. Amorphous ATO nanotubes have a single-layer form, which makes them inefficient for use in photo-catalytic and solar-cell applications. Annealed ATO nanotubes are considered non-stoichiometric if the effect of oxygen partial pressure on the composition is significant. The driving force behind growing crystalline ATO nanotubes is the drawing of oxygen from the atmosphere to the oxygen site, which consequently decreases the concentration of oxygen vacancies in the anatase phase. The small ionization energies of titanium ions produce the stoichiometric defects. A diagram showing Gibbs energy and Kroger-Vink notation to indicate the strong influence of the non-stoichiometric ATO structure is deduced.
A perspective of mesoscopic solar cells based on metal chalcogenide quantum dots and organometal-halide perovskites
(2013-10-01)
Rhee, Jae Hui
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Chung, Chih-Chun
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Diau, Eric Wei-Guang
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應用化學系
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應用化學系分子科學碩博班
We review two types of inorganic nanomaterials-metal chalcogenide quantum dots (QDs) and lead halide perovskites-that serve as prospective light harvesters in hybrid mesoscopic solar cells. Metal chalcogenide QDs are introduced in three parts: chalcogenides of cadmium (CdS, CdSe and CdTe), chalcogenides of lead (PbS and PbSe) and chalcogenides of antimony (Sb2S3 and Sb2Se3). The devices made using these chalcogenide QDs in a liquid-type electrolyte showed the best cell efficiencies, ranging from 3 to 6%. For solid-state QD-sensitized solar cells (QDSCs), the device performances were generally poor; only devices made of Sb2S3 and PbS QDs attained cell efficiencies approaching similar to 7%. In contrast, nanocrystalline lead halide perovskites have emerged since 2009 as potential photosensitizers in liquid-type sensitized TiO2 solar cells. In 2012, the efficiencies of the all-solid-state perovskite solar cells were enhanced to 9.7 and 10.9% using anodes of TiO2 and Al2O3 films, respectively, with 2,20,7,70-tetrakis-(N, N-di-p-methoxyphenylamine) 9,9'-spirobifluorene (spiro-OMeTAD) as a holetransporting material. In 2013, the performance of a TiO2 solar cell sensitized with lead iodide perovskite (CH3NH3PbI3) was optimized further to attain an overall power conversion efficiency eta = 15%, which is a new milestone for solar cells of this type having a device structure similar to that of a dye-sensitized solar cell.
A strategy to design highly efficient porphyrin sensitizers for dye-sensitized solar cells
(2011)
Chang, Yu-Cheng
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Wang, Chin-Li
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Pan, Tsung-Yu
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Hong, Shang-Hao
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Lan, Chi-Ming
We designed highly efficient porphyrin sensitizers with two phenyl groups at meso-positions of the macrocycle bearing two ortho-substituted long alkoxyl chains for dye-sensitized solar cells; the ortho-substituted devices exhibit significantly enhanced photovoltaic performances with the best porphyrin, LD14, showing J(SC) = 19.167 mA cm(-2), V(OC) = 0.736 V, FF = 0.711, and overall power conversion efficiency eta = 10.17%.
A study on utilizing different metals as the back contact of CH3NH3PbI3 perovskite solar cells
(2016)
Behrouznejad, F.
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Shahbazi, S.
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Taghavinia, N.
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Wu, Hui-Ping
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Diau, Eric Wei-Guang
Organic-inorganic halide perovskite solar cells have attracted considerable interest due to their high efficiency and low fabrication cost. Au and Ag are usually used as the back contact metals but have limitations such as Au is too expensive and Ag is unstable. Here, Pt, Au, Ni, Cu, Cr and Ag were studied as the back contact electrodes for perovskite solar cells. We looked at how the work function of metals can affect their photovoltaic characteristics. The compositional and electrical characterizations were studied using X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). The general trend observed was that the shunt resistance and open-circuit voltage of the devices decrease with the decreasing work function of the contact metal. The EIS measurements indicated that the internal resistance of the cell decreases when using spiro-OMeTAD in Au, Ag and Pt devices, whereas in the case of Ni, Cu and Cr devices, the internal resistance of the interface increases, indicating that spiro-OMeTAD is not a good HTM with these metal electrodes. Our results also showed that Cu and Ag were not stable in these devices and that the performance of the Ag device degraded faster than that of the Cu device. Efficiencies of 16.4%, 16.5%, 14.7%, 7.8%, 9.2% and 0.04% were obtained for the devices with Au, Ag, Pt, Ni, Cu and Cr, respectively.
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.
Anisotropic Electric Field Effect on the Photoluminescence of CH3NH3PbI3 Perovskite Sandwiched between Conducting and Insulating Films
(2017-10-19)
Awasthi, Kamlesh
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Wang, Chi-Yung
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Fathi, Amir
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Narra, Sudhakar
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Diau, Eric Wei-Guang
Photoluminescence (PL) of a nanocrystalline film of methylammonium lead iodide perovskite (MAPbI(3)) sandwiched between an electrode of a fluorine-doped tin oxide (FTO) layer and an insulating film of poly(methyl methacrylate) is found to increase and decrease significantly with the application of an external electric field (F-ext), depending on the direction of the applied field, based on the measurements of electrophotoluminescence (E-PL) spectra, i.e., field-induced change in PL spectra. The field-induced change in PL intensity is confirmed to originate from the field-induced change in the number of free carriers which induce radiative recombination, based on temporally resolved E-PL measurements. We propose that an internal field (F-int) exists even without application of F-ext. The anisotropic behavior of the effect of F-ext on PL is interpreted in terms of a synergy effect of F-int and F-ext; both fields are additive with the applied field direction from Ag to FTO electrode (positive direction) or subtractive with the opposite applied field direction (negative direction), where FTO is the positive electrode, resulting in an increased or decreased total electric field as well as quenching or enhancement of PL, respectively. The PL lifetime in the nanosecond region increased and decreased with an application of an electric field in the positive and negative directions, respectively, which is attributed to a field-induced change in the concentration of free carriers.
Anomalous Charge-Extraction Behavior for Graphene-Oxide (GO) and Reduced Graphene-Oxide (rGO) Films as Efficient p-Contact Layers for High-Performance Perovskite Solar Cells
(2018-01-25)
Jokar, Efat
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Huang, Zhong Yi
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Narra, Sudhakar
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Wang, Chi-Yung
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Kattoor, Vidya
Reduced graphene oxides (rGO) are synthesized via reduction of GO with reducing agents as a hole-extraction layer for high-performance inverted planar heterojunction perovskite solar cells. The best efficiencies of power conversion (PCE) of these rGO cells exceed 16%, much greater than those made of GO and poly(3,4-ethenedioxythiophene):poly(styrenesulfonate) films. A flexible rGO device shows PCE 13.8% and maintains 70% of its initial performance over 150 bending cycles. It is found that the hole-extraction period is much smaller for the GO/methylammonium lead-iodide perovskite (PSK) film than for the other rGO/PSK films, which contradicts their device performances. Photoluminescence and transient photoelectric decays are measured and control experiments are performed to prove that the reduction of the oxygen-containing groups in GO significantly decreases the ability of hole extraction from PSK to rGO and also retards the charge recombination at the rGO/PSK interface. When the hole injection from PSK to GO occurs rapidly, hole propagation from GO to the indium-doped tin oxide (ITO) substrate becomes a bottleneck to overcome, which leads to a rapid charge recombination that decreases the performance of the GO device relative to the rGO device.
Application of a dual functional luminescent layer to enhance the light harvesting efficiency of dye sensitized solar cell
(2017-02-01)
Hosseini, Zahra
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Taghavinia, Nima
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Diau, Eric Wei-Guang
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應用化學系
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應用化學系分子科學碩博班
A luminescent coating of CaAlSiN3:Eu2+ particles applied on photoanode (TiO2) layer of SQ1 sensitized solar cell by doctor blading the paste of phosphor particles. The luminescent layer acted as a dual functional layer and enhanced the short circuit current density (J(SC)) by 64% via both scattering effect and downshifting of the photons in 400-600 nm spectral range to photons in 600-800 nm spectral range. Considerable relative enhancement in incident photon to current conversion efficiency (IPCE) up to 350% in 400-600 run spectral range proves the down shifting effect as the dominant factor for the improved performance of dye sensitized solar cell (DSSC).
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.
Assessment of Luminescent Downshifting Layers for the Improvement of Light-Harvesting Efficiency in Dye-Sensitized Solar Cells
(2014-12-01)
Hosseini, Zahra
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Diau, Eric Wei-Guang
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Mehrany, Khashayar
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Taghavinia, Nima
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應用化學系
Luminescence downshifting (LDS) of light can be a practical photon management technique to compensate the narrow absorption band of high-extinction-coefficient dyes in dye-sensitized solar cells (DSSCs). Herein, an optical analysis on the loss mechanisms in a reflective LDS (R-LDS)/DSSC configuration is reported. For squaraine dye (550-700 nm absorption band) and CaAlSiN3:Eu2+ LDS material (550-700 nm emission band), the major loss channels are found to be non-unity luminescence quantum efficiency (QE) and electrolyte absorption. By using an ideal LDS layer (QE=100%), a less absorbing electrolyte (Co-based), and antireflection coatings, approximately 20% better light harvesting is obtained. If the absorption/emission band of dye/LDS is shifted to 800 nm, a maximal short-circuit current density (J(sc)) of 22.1 mAcm(-2) can be achieved. By putting the LDS layer in front of the DSSC (transmissive mode), more significant loss channels are observed, and hence a lower overall efficiency than the R-LDS configuration.
Characterisation of electron transport and charge recombination using temporally resolved and frequency-domain techniques for dye-sensitised solar cells
(2012)
Li, Lu-Lin
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Chang, Yu-Cheng
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Wu, Hui-Ping
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Diau, Eric Wei-Guang
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應用化學系
We review systematically the kinetic characterisation of electron transport and charge recombination in dye-sensitised solar cells (DSSC) using both temporally resolved and frequency-domain techniques. For the temporally resolved approach, charge extraction (CE), transient-photocurrent decay (TCD) and transient-photovoltage decay (TVD) methods are introduced in detail; for the frequency-domain approach, techniques involving electrochemical impedance spectroscopy (EIS), intensity-modulated photocurrent spectroscopy (IMPS) and intensity-modulated photovoltage spectroscopy (IMVS) are presented in detail. The TCD and TVD data are obtained under short-circuit and open-circuit conditions, respectively, and the electron diffusion coefficients and electron lifetimes are extracted from fitting the decay curves accordingly; the IMPS/IMVS results are the counterparts of the TCD/TVD results in the frequency domain. Even though the EIS results are readily acquired, an accurate interpretation of the data requires an appropriate model to determine the internal features of the device. This review provides an account of each technique about its operating principle, experimental setup and data analysis. As case studies for each technique, examples are given to rationalise the observed potential shift, decay coefficients of electron transport and of charge recombination in relation to the corresponding photovoltaic performance of the device.
Co-Sensitization of Zinc and Free-Base Porphyrins with an Organic Dye for Efficient Dye-Sensitized Solar Cells
(2014-12-04)
Wang, Chin-Li
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Shiu, Jia-Wei
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Hsiao, Yen-Ni
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Chao, Pei-Shang
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Diau, Eric Wei-Guang
Co-sensitization of an efficient zinc porphyrin sensitizer (LD14) with its free-base analogue (H(2)LD14) and an organic dye (AN-3) improves the efficiency of the dye-sensitized solar cells. The superior performance of the co-sensitized system is attributed to complementary absorptions of the three dyes, resulting in panchromatic incident photon-to-current conversion efficiency responses at the expense of only slightly lowered open-circuit voltage.
Cobalt Oxide (CoOx) as an Efficient Hole-Extracting Layer for High Performance Inverted Planar Perovskite Solar Cells
(2016-12-14)
Shalan, Ahmed Esmail
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Oshikiri, Tomoya
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Narra, Sudhakar
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Elshanawany, Mahmoud M.
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Ueno, Kosei
CoOx is a promising hole-extracting layer (HEL) for inverted planar perovskite solar cells with device configuration ITO/CoOx/CH3NH3PbI3/PCBM/Ag. The devices fabricated according to a simple solution procedure showed the best photovoltaic performance attaining power conversion efficiency (PCE) of 14.5% under AM 1.5 G 1 sun irradiation, which is significantly superior to those of materials fabricated with a traditional HEL such as PEDOT:PSS (12.2%), NiOx (10.2%), and CuOx (9.4%) under the same experimental conditions. We characterized the chemical compositions with XPS, crystal structures with XRD, and film morphology with SEM/AFM techniques. Photoluminescence (PL) spectra and the corresponding PL decays for perovskite deposited on varied HEL films were recorded to obtain the hole-extracting characteristics, for which the hole extracting times show the order CoOx (2.8 ns) < PEDOT:PSS (17.5 ns) < NiOx (22.8 ns) < CuOx (208.5 ns), consistent with the trend of their photovoltaic performances. The reproducibility and enduring stability of those devices were examined to show the outstanding long-term stability of the devices made of metal oxide HEL, for which the CoOx device retained PCE approximate to 12% for over 1000 h.
Construction of a photoanode with varied TiO2 nanostructures for a Z907-sensitized solar cell with efficiency exceeding 10%
(2014)
Shiu, Jia-Wei
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Lan, Zih-Jian
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Chan, Chien-Yi
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Wu, Hui-Ping
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Diau, Eric Wei-Guang
For Z907-based dye-sensitized solar cells, we constructed photoanodes, layer by layer, containing titania nanostructures of varied types - spherical nanoparticles (NPs), one-dimensional nanorods (NRs), and octahedron-like nanocrystals of varied size (HD1-HD3), in either a bi-layer (BL) or a multi-layer (ML) film configuration. To understand the kinetics of electron transport in these devices, we measured charge extraction, intensity-modulated photocurrent spectra and photovoltage spectra of devices made of either these nanomaterials or hybrid HD-NP composites (HDP). The HD devices featured an excellent characteristic of electron transport and upward-shifted potentials to produce V-OC greater than those of the NP and NR devices, but the latter featured a larger dye loading to give J(SC) greater than that for the former; the devices fabricated with hybrid HDP films showed enhanced J(SC) and balanced V-OC to perform better than their individual counterparts. We constructed the ML devices based on the NP-BL system with additional HDP layers inserted between the two components, NP and SL, to enhance J(SC) so as to attain the best performance, with efficiency of power conversion (PCE) = 10.1%, at a film thickness (L) of 26 mu m. Because of the robust structural feature of the HD films, the devices fabricated with a simple BL film configuration, HD1/SL = 6/3, exhibited the best performance, PCE = 10.2% at L = 29 mu m, which is a promising advance for Z907-based solar cells with a superior and enduring stability of performance for commercialization.
Control of Crystal Structures and Optical Properties with Hybrid Formamidinium and 2-Hydroxyethylammonium Cations for Mesoscopic Carbon-Electrode Tin-Based Perovskite Solar Cells
(2018-09-01)
Tsai, Cheng-Min
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Lin, Yu-Pei
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Pola, Murali Krishna
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Narra, Sudhakar
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Jokar, Efat
Alcohol-based bifunctional ammonium cations, 2-hydroxyethylammonium (HEA(+)), HO(CH2)(2)NH3+, were introduced into formamidinium (FA(+)) tin-based perovskites (HEA(x)FA(1-x)Snl(3); x = 0-1) to absorb light in carbon-based mesoscopic solar cells. We found that HEAP cations play a key role to control the crystal structures, the lattice structures altered from orthorhombic (x = 0) to rhombohedral (x = 0.2-0.4) with greater symmetry. When x was increased to 0.6-1.0, tin and iodide vacancies were formed to generate 3D-vacant perovskites (HEA(x)FA(1-x)Sn(0.6)I(2.33), x >= 0.6) with a tetragonal structure. Tin-based perovskites in this series were fabricated into mesoporous solar cells using one-step drop-cast (DC), two-step solvent-extraction (SE), and SE + 3% ethyl-enediammonium diiodide (EDAI(2)) as an additive. After optimization of device performance with the SE + 3% EDAI2 approach, the HEA(0.4)FA(0.6)SnI(3) (HEAT = 40%) device gave the best photovoltaic performance with J(sc) = 18.52 mA cm(-2)) V-OC 371 mV, FF = 0.562, and overall efficiency 17 = 3.9% after the device was stored for a period of 340 h.
Control of Dye Aggregation and Electron Injection for Highly Efficient Porphyrin Sensitizers Adsorbed on Semiconductor Films with Varying Ratios of Coadsorbate
(2009-12-10)
Lu, Hsueh-Pei
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Tsai, Chen-Yuan
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Yen, Wei-Nan
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Hsieh, Chou-Pou
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Lee, Cheng-Wei
We report the photovoltaic performances and kinetics of femtosecond fluorescence for three zinc-porphyrin sensitizers (YD0-YD2) coadsorbed with chenodeoxycholic acid (CDCA) at three molar ratios on nanocrystalline semiconductor (TiO(2) or Al(2)O(3)) films. The addition of CDCA improved the efficiencies of YD0 and YD1 so that their maximum performance occurred at a dye/CDCA ratio of 1:2, but the presence of CDCA had a negative effect for YD2. Porphyrin aggregation on TiO(2) surfaces not only accelerates the rate of intermolecular energy transfer but also increases the rate of interfacial electron injection, so that the electron injection yields (Phi(inj)) are balanced by these two important factors. As a result, Phi(inj) increased slightly with increasing amount of CDCA for both YD0 and YD1, but decreased for YD2; for this reason, the presence of CDCA failed to improve the photovoltaic performance for YD2, unlike for YD0 and YD1. The cell performances were optimized on TiO(2) films of similar to 10-mu m thickness with a scattering layer of similar to 4-mu m thickness: the efficiencies 4 if power conversion of YD1 and YD2 are slightly smaller than, but near, that of N719, being 6.5% and 6.8%, respectively, compared to 7.3%. Without a scattering layer on the films, the performance of N719 was degraded significantly (6.3%), whereas the efficiencies of YD1 and YD2 decreased only slightly (6.4% and 6.6%), making this series of green sensitizers promising candidates for future light-penetrable photovoltaic applications.
Control of preferred orientation with slow crystallization for carbon-based mesoscopic perovskite solar cells attaining efficiency 15%
(2017-01-14)
Tsai, Cheng-Min
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Wu, Guan-Wei
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Narra, Sudhakar
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Chang, Hung-Ming
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Mohanta, Nayantara
To produce mesoscopic carbon-electrode-based solar cells free of a hole-conduction layer, we developed a simple one-step drop-cast method (temperature 20 degrees C, relative humidity 50%) to grow uniform and compact perovskite nanocrystals via slow crystallization (SC). X-ray diffraction (XRD) results indicated that perovskite nanocrystals produced inside the mesoporous TiO2/Al2O3/C layers according to our SC approach with N-methyl-2-pyrrolidone (NMP) as a precursor solvent showed a preferred orientation at facet (004) with large crystalline grains, whereas those produced with other solvents or via thermal annealing (TA) methods showed greater intensity at facet (220) with small crystals. After the SC (NMP) procedure was completed, additional TA treatment would change the preferred orientation from (004) back to facet (220), which would break the connectivity and lose the uniformity of the crystals, causing the grains to become significantly smaller. Transient photoluminescence (PL) decay profiles of the SC devices made with four precursor solvents, NMP, g-butyrolactone (GBL), dimethylformamide (DMF) and dimethyl sulfoxide (DMSO), were recorded to show the trend of charge separation kinetics of the perovskite crystals inside the mesoporous films, which is consistent with the trend of the corresponding device performance showing the same order. The SC (NMP) device attained the best efficiency of power conversion (PCE), 15.0%, with average value (13.9 +/- 0.5%), which is much superior to those devices from either the traditional one-step TA (DMF) method (5.2 +/- 1.0%) or the traditional sequential TA method (10.1 +/- 0.7%). This work emphasizes the significance of the control of preferred orientation of perovskite nanocrystals using the SC approach, to obtain high-performance carbon-based mesoscopic solar cells with excellent reproducibility and stability.