Browsing by Author "Yeh, Shih-Chieh"

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Facile Solution Dropping Method: A Green Process for Dyeing TiO2 Electrodes of Dye-Sensitized Solar Cells with Enhanced Power Conversion Efficiency
(2015-01-01)
Yeh, Shih-Chieh
;
Lee, Pei-Heng
;
Liao, Hua-Yang
;
Chen, Yu-You
;
Chen, Chin-Ti
A simple solution dropping method was established for sensitizing TiO2 in the fabrication of dye-sensitized solar cells (DSCs). As compared with the conventional immersion dyeing process, this solution dropping method is very fast, taking less than similar to 5 min vs >5-10 h typically required in the traditional immersion dyeing process. There is much less organic solvent and dye substance (95% less) used in the dyeing TiO2 process and hence significantly less disposal of chemical wastes from device fabrications. Therefore, this facile solution dropping method is a greener process than the immersion dyeing process. Moreover, the solution dropping method is superior to the immersion dyeing process in terms of power conversion efficiency (PCE) of the device. We have acquired compelling evidence through dye uptake assessment of TiO2 electrodes, depth profile assay by SEM-EDX, and charge dynamic characteristics from transient photovoltage/photocarrent analysis indicating that the elevated dye loading level of a TiO2 electrode is the main cause responsible for increasing short-circuit current and hence the PCE of DSCs. Three types of dye were used in this study to demonstrate the superiority of the solution dropping method, including classical N719 (a ruthenium transition metal complex), 1P-PSS (a metal free organic dye), and newly synthesized ATT (a beta-pyrrole carbon-conjugated zinc tetraphenylporphyrin). Using the solution dropping method, dye uptake was improved from 3.0 X 10(-7) to 9.9 X 10(-7) mole cm(-2), 5.3 X 10(-7) to 6.6 X 10(-7) mole cm(-2), and 4.7 X 10(-8) to 3.92 X 10(-7) mole cm(-2) for N719, 1P-PSS, and ATT, respectively. In addition, the PCEs, averaged from 30 or 40 tested devices each with a 0.4 cm X 0.4 cm active area, were all improved from 8.1% to 8.5%, 5.9% to 6.6%, and 4.196 to 6.7% for N719, 1P-PSS, and ATT, respectively.
Oxasmaragdyrins as New and Efficient Hole-Transporting Materials for High-Performance Perovskite Solar Cells
(2017-09-20)
Mane, Sandeep B.
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Sutanto, Albertus Adrian
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Cheng, Chih-Fu
;
Xie, Meng-Yu
;
Chen, Chieh-I
The high performance of the perovskite solar cells (PSCs) cannot be achieved without a layer of efficient hole-transporting materials (HTMs) to retard the charge recombination and transport the photogenerated hole to the counterelectrode. Herein, we report the use of boryl oxasmaragdyrins (SM01, SM09, and SM13), a family of aromatic core-modified expanded porphyrins, as efficient hole-transporting materials (HTMs) for perovskite solar cells (PSCs). These oxasmaragdyrins demonstrated complementary absorption spectra in the low-energy region, good redox reversibility, good thermal stability, suitable energy levels with CH3NH3PbI3 perovskite, and high hole mobility. A remarkable power conversion efficiency of 16.5% (V-oc= 1.09 V, J(sc) = 20.9 mA cm(-2), fill factor (FF) = 72%) is achieved using SM09 on the optimized PSCs device employing a planar structure, which is close to that of the state-of-the-art hole-transporting materials (HTMs), spiro-OMeTAD of 18.2% (V-oc = 1.07 V, J(sc) = 22.9 mA cm(-2), FF = 74%). In contrast, a poor photovoltaic performance of PSCs using SM01 is observed due to the interactions of terminal carboxylic acid functional group with CH3NH3PbI3.
Solvent-assisted crystallization via a delayed-annealing approach for highly efficient hybrid mesoscopic/planar perovskite solar cells
(2017-12-01)
Sutanto, Albertus Adrian
;
Lan, Shiang
;
Cheng, Chih-Fu
;
Mane, Sandeep B.
;
Wu, Hui-Ping
The formation of a dense and uniform perovskite film with large grain is an important factor for getting excellent device performance. Here, we report an optimized solvent-assisted crystallization procedure followed by a delayed annealing for easy and reproducible fabrications of perovskite solar cells with a hybrid mesoscopic configuration. The working electrode contains a mesoporous TiO2 scaffold layer of 100 nm deposited on FTO substrate with a thin TiO2 blocking layer. The devices in this study were assembled using all commercially available materials without any extensive modification. Formation of uniform and pin-hole free perovskite nanocrystals with film thickness 200 nm on top of the scaffold layer was achieved via an optimized solvent assisted crystallization method. A much smoother perovskite layer was achieved with a delayed annealing for a certain period. The best performing device was obtained at the annealing delayed for 60 min, giving the power conversion efficiency 16.9% with an average value 15.4% obtained from 60 devices.
Structure-Property Relationship Study of Donor and Acceptor 2,6-Disubstituted BODIPY Derivatives for High Performance Dye-Sensitized Solar Cells
(2017-10-20)
Yeh, Shih-Chieh
;
Wang, Li-Jing
;
Yang, Hong-Ming
;
Dai, Yu-Huei
;
Lin, Chao-Wen
Seven donor and acceptor 2,6-disubstituted 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) dyes have been synthesized and characterized. Including MPBTCA, which is a known compound, the seven BODIPY dyes have been characterized by varied physical methods, such as UV/Visible absorption spectroscopy, low energy photo-electron spectroscopy (AC-2), and HOMO-LUMO DFT/TDDFT calculation. All seven BODIPY dyes have absorption lambda(max) around 535-545 nm, which is significantly longer than 499 nm of 4,4-difluoro-1,3,5,7,8-pentamethyl-4-bora-3a,4a-diaza-s-indacene (PM 546). Having structural variation on donor group, acceptor group, donor pi-spacer, acceptor pi-spacer, and the substituent on boron, some BODIPY dyes exhibit small extinction coefficients or spectral integrals in solution (MPCtBTCA, MPBT-pyO, MPBTT-pyO, MTBTCA), broadening absorption spectral profile (MTBTCA), weak intramolecular charge transfer characteristics (MPBT-pyO, MPBTT-pyO, MTBTCA), too low LUMO energy level (PPBTCA), or insufficient dye-uptake by TiO2 FTO (MPBT-pyO, MPBTT-pyO, MTBTCA). Two of the seven BODIPY dyes, MPBTCA and MPBTTCA, do not show the adverse properties like other BODIPY dyes. With our improved TiO2 FTO (fluorine doped tin oxide) dyeing method, namely a solution dropping method, high performance dye-sensitized solar cells (DSCs) have been realized by MPBTCA and MPBTTCA photosensitizers. Power conversion efficiencies of 6.3 and 6.4% have been achieved by MPBTCA and MPBTTCA DSCs, respectively. To the best of our knowledge, MPBTCA and MPBTTCA are the most efficient dyes for the donor and acceptor 2,6-disubstituted BODIPY DSCs so far.